The problem with the luft is that humidity isn't just a property of the air in the house, it's a property of the whole building fabric. Replacing the air with new air of lower absolute humidity will give a temporary relief; but that will be very temporary as the humidity in the walls, floors and building materials is released back into the air again. Continuous ventilation through PIV, MEV or MVHR is superior as (in addition to increased efficiency/comfort from not shocking the house with cold air) it continuously ventilates so the building fabric doesn't have a chance to get damp.
I open all windows in the morning. Then, even with a bit of sunshine get massive solar gain during the day. In the evening we have a log burner that pulls a massive amount of fresh air in the house. Zero condensation.
I've been opening bedrooms windows at Front & back plus back door for about 10 mins in morning. Humidity dropped from >65% to ~52% downstairs & 63% upstairs. I'll try opening early evening for a few mins as well.
The best and most efficient way of exploiting the principle explained is to fit a heat/energy recovery ventilator. This means that the incoming fresh air is warmed by the outgoing stale air (the streams do not mix) and therefore you don't have to open any windows and lose heat but instead get fresh (dry) air all the time inside the house. There are no condensation or mold issues despite the house being 'hermetically' sealed and the house stays warm with minimal heating required. I have fitted one and the relative humidity in the house is mostly between 50% and 65% at around 20°C and I live in very humid Devon next to the sea. HRVs should be fitted as standard to all new housing but alas they are not or grants given to retro fit them.
This sounds like a great idea! I have a few questions if you don’t mind answering them: Is it cost prohibitive? Can it be self installed? Do you recommend any specific product / manufacturer?
@@GreenWhereItSuits I have installed HRVs myself in two houses which I have owned. One was a bungalow which is the easiest to install and a house I live in now which is a 4-bed detached. This was a bit more problematic as you have to get ducting downstairs, in this case I fed the 100 mm ducting down through fitted wardbrobes to the living and dining rooms for fresh air in; kitchen and utility for stale air out. So yes, they can be installed as DIY and very easy in a bungalow. A house requires a bit more thought. HRVs are designed to run continuously replacing the entire air of the house every couple of hours. To make them efficient the house needs to be fairly air tight. During the summer we leave the HRV off as the windows are left open. The HRV draws about 15 to 20 watts depending on setting. Costs vary on size of house but mine was around £400. It's been running faultlessly for 13 years now. It is made by Vent-Axia. www.vent-axia.com/mechanical-ventilation-heat-recovery-mvhr
Wow, seems like this is perfect for me, I got a house in Devon, sold brick, cement render, it keeps getting black mould everywhere from the dampness. Would this work for me? I was going to add some ventilation bricks. But now that you said house should be sealed I'm thinking not hmm 🤔
Excellent explanation of relative humidity, thank you for that. But as some people have hinted on the comments, the same amount of already heated, warm air, will leave the house as the volume of cold air brought in. So you are constantly paying to reheat the house once or twice a day. This is a hidden cost, that soon adds up. This is where the dehumidifier has a massive advantage because you have none of these reheating costs.
I totally agree with you there. The inspiration for this video came from the energy support forums I frequent that sees posts by those on low incomes where the cost of a dehumidifier is too large of an initial outlay or with older, perhaps unmaintained properties that are dealing with condensation and mould issues. In future videos it might do me well to mention that, however, I wonder if I’d receive such informative responses had I done so!
We vent the house for 10 mins if the heating hasn't been on. We also use a dehumidifier to help dry clothes in a small sealed room and when using showers, have a small window open to vent humid air, which we close soon afterwards. We're aware it takes more energy to heat air that is more humid, so doing everything we can to lower humidity without losing heated air, hopefully makes our heating more efficient
You people who have blithely talk about keeping the room warm, clearly have no idea how the other half lives. The warmest room in my house never gets above 14°C in winter. The relative humidity ranges between 70% and 80% humidity. It's impossible to make any difference to this even with 2 heaters running which takes up the major part of my small income. I'm happy for you all that you don't have the same situation. In all my previous hinges I had a multi fuel burner and/or central heating (which I hardly used) without an efficient means of heating the situation is extremely difficult to tackle. Good bless you all and Happy Christmas!
The idea that heating is needed to alleviate the humidity is part of the misconceptions that can leave those houses continually damp. What is 'wrong' with Lüften is that it doesn't actively focus on extracting humid air as a priority. Given most houses are leaky (air-wise) then choosing to actively extract the humid air (rather than passively letting warmed air leak away) is a clear benefit in reducing humidity - I was in that situation with our 'new' bungalow that had no extraction and water (condensation) streaming down the wall last winter. Humidistat extractors greatly help (Kitchen & Bathroom). In some older properties the underfloor solum (soil) isn't sealed, so moisture will evaporate from the soil into the house increasing humidity. Simply putting a large plastic sheet (~1000guage) with 75mm turn ups onto the underfloor solum will also reduce condensation. It's a case of beating all the possible causes into submission, especially those you can easily address.
A lot of the comments worry about the cost of re-heating the cold air compared with running a dehumidifier. I don't know about the latter, but I've done the following calculation which might be of interest: Our second bedroom, which has a condensation problem, has a volume of 20 cubic metres. At 1.2kg/cubic meter, the mass of air in the room is 24kg. It takes about 1kj to raise the temperature of 1kg of air by 1 degree C. Raising the temperature of the 24kg of air in the room by 10 degrees C will take 240kJ. 1kWh = 3,600kJ. Therefore It should take 0.07kWh to warm the air in the room by 10 degrees C. The cost of doing this is 2p (at 30p per kWh.) Even allowing for a bit more to account for the inefficiency of the boiler, and some to reheat a thin layer of the walls and ceiling, this doesn't seem like much. Have I made a big blunder anywhere?
Its not just the air that you are heating up though. The cold air will drop the temperature of the room walls, Ceiling floor and furnishings which will have a considerably higher heat capacity than the air. I would be delighted if I could warm a room by electricity for 2p and that would mean I would only need a 1kw heater on for 4 minutes, but it doesn't work.
@@billbimson2408 You also need to do the thermal conduction and thermal capacity calculations of the walls, furniture and drapes (curtains) for the limited 5-10 minutes of Lüften. While curtains blowing in the wind could cool rapidly through the whole material mass, the walls and furniture tend to have low conduction rates relative to their thermal mass so are only cold to touch at the surface. Most fabrics and furniture is already warm to the touch (the joy of flannelette sheets and a woolly rug;-) indicating they have low conductivity relative to their heat capacity. Overall the Lüften is a deliberate exchange of air, not an attempt to cool down the heat store of the body of the house and it's contents. Also remember that you already have somewhere between 5-15 air changes per hour (ACH) unless in an actively well sealed modern Passiv house. At 5 ACH that's 12 minutes of continuous Lüften, 5 times per hour, so it is more like the 2p suggested. The key element is to understand and appreciate when, why and how to do the Lüften to actively remove the 'warm damp (high absolute humidity) air' and swap it for cool dryer (low absolute humidity) air at a time when the differential is best and you already have your 'warm clothes' on. I know that it's funny foreigner stuff practised for centuries (and we used to do it), but it's not a reason not to update mental models. It's the ill fitting mental models that are the major hindrance to warmer dryer homes.
I'd say using a dehumidifier is cheaper overall, but what do you do when you can't afford the upfront cost of a dehumidifier but suffer with condensation and mould?
@@GreenWhereItSuits Are you mental? You are advocating your ridiculous method up there ^, but recommending something entirely different here! "When you can't afford to buy a dessicant dehumidifier, pay for more gas, so then you definitely won't be able to afford a dehumidifier." You are 'green', as in naive and not very well informed.
I noticed in the comments a lot of people are worried about heat loss, this would be very low allowing moist air to leave the building over a short period, as there is still a lot of heat trapped within the building fabric and furniture.
Well explained and great illustration of RH. I use an online calculator to convert RH to Absolute Humidity so I can see grams of water per cubic meter of air. Thanks for a great video 👍
Very informative explination on how humidity and condensation works. This may make sense in a cold climate, I don't think it works in a hot costal climate where during the day it is 30C+ at night it is 20C+. You will get some benefit, but the discomfort of that heat makes this impractical. Even if the same dynamics could work. Still just keeping your windows open obviously helps, but crime and other factors can make that not feasible either. I found a dehumidifier was just easier.
Yes Hot and Humid climates need a shift in when to do the exchange, assuming there is a point where it's advantageous. If Air Conditioning (AC) is common you are fighting a different enemy!
I live in northern Ireland,where average humidity outdoors (over a 12 month period) is 90% inside my house over 80% if I run a dehumidifier all night I collect around 10 litre water a night . Humidity may be down to 70-75%.i sleep even in winter with my window open ! Living in this shit hole is a nightmare! Rain and storm 300+ days a year
We live by a forest a mile from the sea and hover around 70% humidity, we don't have any mould anywhere because we keep the temperature in all rooms above the dew point. Simple. We don't have mechanical extraction either.
Isn't it cheaper to just use a dehumidifier, the electrical cost of running contributes to heating the house, and also extract heat from the water vapour as it condenses on the dehumidifier coils instead of transferring the heat to the cold windows or worse out the window.
I have kept the single glazed metal frame window in the bathroom, It streams with condensation , which runs thro' the frame to outside, ( some times forming icicles ) , yes I loose 40w more heat than a double glaze window, & it is not as good as a £3000 MVHR , but that might have a 40w fan.
Having brick and plaster walls helps keep the house heat in the wall while the air is exchanged in the 5 minutes of Lüften. If the house walls are low thermal capacity then the air-change will make for larger fluctuations in temperature (longer to re-warm and needing active heating). I've done a "simplified Relative Humidity (RH) 'psychrometric' chart" (can be done in Excel) showing those constant 'water' lines across the RH-Temperature chart. The equations are in the "CIBSE CPD module 7 (2009)" (web search should find it).
Your house needs ventilation for other reasons than humidity BUT this method is not free. You are dumping all your heat. Get a dehumidifier! Because it gives out up to 50% more heat than the same electricity used in an electric heater. That is because the energy you had to use to boiling your kettle for example, to release the humidity, is returned as heat when you condens it out again. They are also more effective for preventing damp and are great for drying clothes.
I agree it’s not free, however, you can minimise cost depending on when you do it. In the video I mention after dinner but if you do it before leaving for work, providing you have a south facing property the solar gain may offset some or all of the heat losses - depending on where you are and the makes up of your property.
you are only dumping the heat in the air . The majority of the buildings heat is in the walls. To raise 100m3 air by 10c needs 0.33Kwh of heat ... so a normal house heating outside air 1-3Kwh depending on temp etc ( is my maths right ?
@brackcycle9056 we must also add the lost latent heat of the moisture to the calculation. But an additional advantage is that dehumidifying is continuous and more comfortable. It also makes good battery top-up water.
I mention doing this after lunch, but I practice it after we have showered in the morning which then allows solar gain to work on our south facing windows.
I’ve thought upstairs works best as humid air rises, however, so does warm air. Perhaps my house has a warmer upstairs than downstairs as when I’ve trialled the dehumidifier in the downstairs hall it seems to capture more.
Lol but if you dropped your house temperature to 5 to 7°c by opening all the windows to heat it back up to about 21°c would cost a lot more than running a dehumidifier to get rid of the extra moisture. 😂
Tried this and can confirm it doesn’t work. To bring the humidity down from 85(!) after having windows open, I had to have heating on all night along with my industrial dehumidifier on at lowest setting. I’ll stick with keeping the windows shut and having my dehumidifier on all day as before - costs a lot less!!!
Dehumidifiers are very efficient there is no denying that. How do you propose lowering the internal humidity of the property WITHOUT a dehumidifier, which is the subject of the video? If you perform this in the morning before going out for the day, solar gain will help introduce heat back into the property. If you are not in a detached property you will also gain some thermal benefit. That's without mentioning that the thermal makeup on the house will not have dropped to 7 degrees, and dryer air costs less to heat that humid air. Finally, at 5 degrees, you do not need to replace ALL of the air to benefit. As I mention in the video, fully saturated air at 10 degrees Celsius will significantly lower humidity levels when warmed to 19/21 degrees.
+1 for PIV, got our main bedroom down from 75-85% to a steady 50%. The heating is definitely kicking in more but the house is mold free, have had a clear nose and no coughing for the first time in years so well worth it to me. If you're happy wiring a spur it's a pretty simple install too, about £400 in total for me
Repost since I missed one of AI many word swaps! Got dehumidifiers running almost 24/7. In closed rooms with little use I'm still taking over 1 litre a day out. This way I'm drying down the room more than 10 mins + residual or whatever and avoiding having to reheat. I run meters too and the rate of rehumidifying is fierce! Faster than the rate of a 20 litre Meaco in one room can reduce it. Bearing in mind that size of unit is aimed at a small house, not one room. Your idea of good if the inherent dampness of the building is low. My dehumidifiers are slowly taking out less and less. Slowly!
You didn't mention about dew point. If the dew point outside is higher than inside then opening windows will make the humidy go up. The dew point is usually higher outside on really warm days and rainy days. I use my own personal weather station to give me local outside temperature and humidity readings that also gives me the dew point automatically. I can then use the inside temperature and humidy level to work out the inside dew point using a dew point calculator. However I do feel that during the winter if you open your windows even if the dew point is lower outside then you are just wasting energy and have to heat up that air again and the cost of gas and electricity is high. I use a dehumidifier and it costs about 5p an hour and helps to dry the air that in turn the house heats up faster. It is also safe to have a relative humidy level of 65% in your house. It is a bad advice that it has to be 60% or lower and scientific tests have proven this. Trust me I have never had trouble with mold or condensation or bed bugs and our house is old. 70% is where it gets too high.
It isn’t necessary to discuss the dew point but I appreciate that it would be of benefit for people to understand. At 06:10 I provide a guide that discusses an outside temperature of 9°C at 10°C at 100% relative humidity which is the same thing as the dew point. I also have humidity in the high 60s and 70s without the use of dehumidifier and have only had issues (besides condensation) with mild in a previously unvented and unheated downstairs cupboard. This video is aimed at those where humidity is causing issues and do not have a dehumidifier. I appreciate the feedback you have given
1:40 I’m sorry but this is correct on paper but doesn’t correlate to real life. My room is 17 Celsius at 70% humidity… I put the fan heater on to increase the temperature and keep humidity the same but that’s certainly not what happened… the temp went from around 18 to 22 but the humidity sky rocketed to 80%. Look people it’s fcuking near impossible to lower humidity whilst raising the temp without a dehumidifier. Obviously there’s endless variables but in my experience, raising the temp always raises humidity. I mean I do have 4 fat plants in my room and have only ever tried to lower/raise humidity with plants in the room so can’t speak for plant less spaces.
My appartment has MVHR but these systems are still not 100% efficient. For an experiment I bought an efficient dehumidifier and turned off the MVHR. So instead I now run the unit 4-6 hrs. a day to reduce humidity and prevent mold. Always A LOT of water in the tank afterwards. This way the enthalpy of condensation stays in the appartment. So far it seems to work out as we have temperatures close to freezing for almost two weeks now and so far still don't turn on the heater ans have ~22°C inside. With the MVHR running on the lowest setting I'd be running in the low 20s and Mrs. General be demanding to turn on the heated floors. So far I'm happy but I'll keep monitoring the cost if it is worth it financially. As I pay 11.5cents per kwh for district heating and 38cents per kwh for electricity. After last night the device shut off after consuming 1.8kwh and there were almost 4l of water in the tank. Roughly measured 3.85l with 1l mugs.
Excellent advice, but have you ever heard the mainstream media tell people this clearly? Also, drier air is easier to heat, despite the heat you lost venting the house.
this is a good idea but it's not quite right. 100% humidity doesn't automatically equal condensation. condensation can happen at 10C, 17C or 24C - it depends on the dew point. Your point about cold air being drier is absolutely correct though.
In my example I discuss relative humidity by keeping the water content (vapour) static and alter the air temperature to increate and decrease the relative humidity. Eventually I reduce the temperature to a point where the water vapour in the air goes beyond 100% relative humidity (the dew point) and begins to condense.. That isn't to say that condensation occurs only at low temperatures. If you keep a room at any given temperature above freezing, and introduce more and more humidity, it will eventually reach a point where the air is fully saturated (100% relative humidity / the dew point) and with more moisture added you will see condensation form. Interestingly, the dew point below freezing becomes the frost point.
@@cooliocrib4409 I am in the UK. According to the met its 10c where I am in the west mids but a bit windy. Currently no heaters on and its 18.3c according to my CH thermostat. I opened the windows earlier and it went down to 17 for a bit. Mid terrace council house built in the 1960s. Polystyrene balls in the cavity, about 250mm of insulation in most of the loft. There is a hole where the F and E and immersion used to be that I haven't got around to. Double glazing installed 15 years ago. Had 8 air vents in the house originally (had a coal fire before) size of 2 house bricks each, now down to 5. Have those plastic covers but still let in air. Heating kicks in of an evening usually. Only 5 radiators in the whole house- only 1 in living room is a big 1200mm type 22 the others are type 11 and 800 x 600mm
Great explanation... but just get a decent size dehumidifier. If your house feels damp it will take around a month to dry out the walls of your home. Letting out all the heat every night is going to add significantly more to your energy bill than a dehumidifier running cost, and such a strategy is not going to be able to cope with the amount of moisture cooking and drying washing creates. I got one recently and it's made a huge improvement to our home's comfort.
@GreenWhereItSuits initially got as 12L Daewoo unit but it felt a bit inadequate. Got an 18L Meaco Arete 2 instead (it's Costco's special version of the 20L) and have been really happy with it. It just stays on all the time and does its thing in the background.
Instead of using a dehumidifier, you are simply heating cold air and allowing what warm air is in your shelter to escape. That's not a very good solution in a cold climate, when heating is more expensive than a simple dehumidifier. Also, you are ignoring the high humidity in that cold air, (above 75% is great for letting black mold get into your house), then you warm it up (and the black mold grows and spreads). Water vapor is lighter than regular air (with about 55% relative humidity); if you do vent like this, open upstairs windows slightly, till the air cools, then shut them. One of the big problems is that people live in apartments and houses with "open concepts" (fewer walls and doors). There are low humidity areas, (like living rooms, without water); and, there are high humidity areas, (bathrooms and kitchens, with lots of water). Cook in a kitchen, that is vented, not an open cooking area that allows moisture into the dining area and living room, (great smells, maybe, but high humidity going everywhere); put the washer and dryer into their own room or in the kitchen (not where they dampen the entire basement or near a hallway to spread the damp into the whole house); and, vent the bathrooms, (I'd leave a bathroom fan on 24/7 to vent an apartment), as a bath, shower, sink, and toilet produce more humidity than everything else in a house.
Except it's the same temperature! Maybe you mean to say humid air has more specific heat capacity and higher thermal conductivity so can transfer heat away from something warmer more effectively.
You know those little vents on your windows... Yeah this. If your happy just to vent heat and have to re heat your home, yes you can lower the humidity thos way. Much more energy efficient to use a dehumidifier though. Or if you want, a heat exchanging unit, the simplest i hve seen was built in to an in wall extractor fan that had in and out in one unit. Or have a proper system with full hvac / mvhr.
My in-laws have a beautiful analog hygrometer/thermometer! I believe digital ones still have their place, particularly being able to monitor the home remotely or even just making sure my children's bedrooms are comfortable without disturbing their sleep.
Modern digital hygrometers are cheap and reliable and plenty accurate enough. (pack of 5 for £13). What is missing is a "simplified Relative Humidity (RH) 'psychrometric' chart" (see my other comment for sources). Without a suitable chart most folks don't know what to do with the magic numbers the hygrometers generate!
This is nonsense! Just advocating to remove warm air from your house (albeit potentially high humidity), replace it with cold (albeit drier) air and then reheat the air from scratch. Waste of energy heating, discarding and then reheating air. The most cost effective way to deal with high humidity is a dessicant dehumidifier. Low running cost, will remove excess moisture from air making it easier to heat and less humid. Unless you have heat recovery positive pressure ventilation, this idea is ridiculous. Best to insulate and draught proof as well as possible, rely on momentary door openings and trickle vents in windows to exchange fresh air, and manage humidity with a dessicant dehumidifier. Any other suggestion for comfortable cheap living at lower temperature where dewpoint can become problematic is just clickbait!
This video came about through hearing the stories of low-income households that are suffering with mould and do not have the financial means to purchase a dehumidifier outright. This approach will lower the humidity in their home. If they do this in the morning the property can benefit from solar gain, and if they are not a detached property they will receive some heat input from the surrounding properties. For that reason, suggesting the use of a dehumidifier on a video that explains how to lower humidity without one is somewhat missing the point. I myself have a dehumidifier and it is very efficient, but we must be mindful that not everyone can afford such luxuries even if it costs less in the long run.
I've totally rejected the desiccant humidifiers as they are generally one shot wonders pandering to those who aren't aware of their problems. Another commenter notes how cheap it is to actually reheat the air (couple of pence). It's not a cost driver relative to comfort, mould, etc.
Humidity isn't a problem if the house is kept constantly warm, if you let it heat and cool again then you will have problems. We live close to a forest and the sea, our house is around 70% moisture in winter and we don't have any problems. This guy has no idea what he's talking about.
Humidity can still be a problem even if constantly warm. All you need it too many cooking pots without lids, too many showers, natural indoor clothes drying, too many people breathing, etc. Had a colleague with a rental property where the tenants, as a family, did karate/judo and washed their kit many times a week and let it drip dry, he ended up buying a high speed spin dryer for the laundry aspects!
The reason I’m here is because I need to lower the humidity from 70 to 45/50 WITHOUT lowering the temperature. I need it to be from 23-25 Celsius sitting at 45/50% humidity but I can’t afford a dehumidifier atm-.-
The problem with the luft is that humidity isn't just a property of the air in the house, it's a property of the whole building fabric. Replacing the air with new air of lower absolute humidity will give a temporary relief; but that will be very temporary as the humidity in the walls, floors and building materials is released back into the air again. Continuous ventilation through PIV, MEV or MVHR is superior as (in addition to increased efficiency/comfort from not shocking the house with cold air) it continuously ventilates so the building fabric doesn't have a chance to get damp.
If you keep doing it the building humidity will lower.
I open all windows in the morning. Then, even with a bit of sunshine get massive solar gain during the day. In the evening we have a log burner that pulls a massive amount of fresh air in the house. Zero condensation.
I've been opening bedrooms windows at Front & back plus back door for about 10 mins in morning. Humidity dropped from >65% to ~52% downstairs & 63% upstairs. I'll try opening early evening for a few mins as well.
The best and most efficient way of exploiting the principle explained is to fit a heat/energy recovery ventilator. This means that the incoming fresh air is warmed by the outgoing stale air (the streams do not mix) and therefore you don't have to open any windows and lose heat but instead get fresh (dry) air all the time inside the house. There are no condensation or mold issues despite the house being 'hermetically' sealed and the house stays warm with minimal heating required. I have fitted one and the relative humidity in the house is mostly between 50% and 65% at around 20°C and I live in very humid Devon next to the sea. HRVs should be fitted as standard to all new housing but alas they are not or grants given to retro fit them.
This sounds like a great idea! I have a few questions if you don’t mind answering them:
Is it cost prohibitive?
Can it be self installed?
Do you recommend any specific product / manufacturer?
@@GreenWhereItSuits I have installed HRVs myself in two houses which I have owned. One was a bungalow which is the easiest to install and a house I live in now which is a 4-bed detached. This was a bit more problematic as you have to get ducting downstairs, in this case I fed the 100 mm ducting down through fitted wardbrobes to the living and dining rooms for fresh air in; kitchen and utility for stale air out. So yes, they can be installed as DIY and very easy in a bungalow. A house requires a bit more thought. HRVs are designed to run continuously replacing the entire air of the house every couple of hours. To make them efficient the house needs to be fairly air tight. During the summer we leave the HRV off as the windows are left open. The HRV draws about 15 to 20 watts depending on setting. Costs vary on size of house but mine was around £400. It's been running faultlessly for 13 years now. It is made by Vent-Axia.
www.vent-axia.com/mechanical-ventilation-heat-recovery-mvhr
Wow, seems like this is perfect for me, I got a house in Devon, sold brick, cement render, it keeps getting black mould everywhere from the dampness. Would this work for me? I was going to add some ventilation bricks. But now that you said house should be sealed I'm thinking not hmm 🤔
When ghostbusters said ‘don’t cross the streams!’- they were right.
Excellent explanation of relative humidity, thank you for that. But as some people have hinted on the comments, the same amount of already heated, warm air, will leave the house as the volume of cold air brought in. So you are constantly paying to reheat the house once or twice a day. This is a hidden cost, that soon adds up.
This is where the dehumidifier has a massive advantage because you have none of these reheating costs.
I totally agree with you there. The inspiration for this video came from the energy support forums I frequent that sees posts by those on low incomes where the cost of a dehumidifier is too large of an initial outlay or with older, perhaps unmaintained properties that are dealing with condensation and mould issues.
In future videos it might do me well to mention that, however, I wonder if I’d receive such informative responses had I done so!
We vent the house for 10 mins if the heating hasn't been on. We also use a dehumidifier to help dry clothes in a small sealed room and when using showers, have a small window open to vent humid air, which we close soon afterwards. We're aware it takes more energy to heat air that is more humid, so doing everything we can to lower humidity without losing heated air, hopefully makes our heating more efficient
You people who have blithely talk about keeping the room warm, clearly have no idea how the other half lives. The warmest room in my house never gets above 14°C in winter. The relative humidity ranges between 70% and 80% humidity. It's impossible to make any difference to this even with 2 heaters running which takes up the major part of my small income. I'm happy for you all that you don't have the same situation. In all my previous hinges I had a multi fuel burner and/or central heating (which I hardly used) without an efficient means of heating the situation is extremely difficult to tackle. Good bless you all and Happy Christmas!
The idea that heating is needed to alleviate the humidity is part of the misconceptions that can leave those houses continually damp. What is 'wrong' with Lüften is that it doesn't actively focus on extracting humid air as a priority.
Given most houses are leaky (air-wise) then choosing to actively extract the humid air (rather than passively letting warmed air leak away) is a clear benefit in reducing humidity - I was in that situation with our 'new' bungalow that had no extraction and water (condensation) streaming down the wall last winter. Humidistat extractors greatly help (Kitchen & Bathroom).
In some older properties the underfloor solum (soil) isn't sealed, so moisture will evaporate from the soil into the house increasing humidity. Simply putting a large plastic sheet (~1000guage) with 75mm turn ups onto the underfloor solum will also reduce condensation. It's a case of beating all the possible causes into submission, especially those you can easily address.
lol whatever.
A lot of the comments worry about the cost of re-heating the cold air compared with running a dehumidifier. I don't know about the latter, but I've done the following calculation which might be of interest:
Our second bedroom, which has a condensation problem, has a volume of 20 cubic metres.
At 1.2kg/cubic meter, the mass of air in the room is 24kg.
It takes about 1kj to raise the temperature of 1kg of air by 1 degree C.
Raising the temperature of the 24kg of air in the room by 10 degrees C will take 240kJ.
1kWh = 3,600kJ.
Therefore It should take 0.07kWh to warm the air in the room by 10 degrees C.
The cost of doing this is 2p (at 30p per kWh.)
Even allowing for a bit more to account for the inefficiency of the boiler, and some to reheat a thin layer of the walls and ceiling, this doesn't seem like much. Have I made a big blunder anywhere?
Psychrometric charts for the win on all those HVAC style calculations!
Its not just the air that you are heating up though. The cold air will drop the temperature of the room walls, Ceiling floor and furnishings which will have a considerably higher heat capacity than the air. I would be delighted if I could warm a room by electricity for 2p and that would mean I would only need a 1kw heater on for 4 minutes, but it doesn't work.
@@billbimson2408 You also need to do the thermal conduction and thermal capacity calculations of the walls, furniture and drapes (curtains) for the limited 5-10 minutes of Lüften. While curtains blowing in the wind could cool rapidly through the whole material mass, the walls and furniture tend to have low conduction rates relative to their thermal mass so are only cold to touch at the surface.
Most fabrics and furniture is already warm to the touch (the joy of flannelette sheets and a woolly rug;-) indicating they have low conductivity relative to their heat capacity. Overall the Lüften is a deliberate exchange of air, not an attempt to cool down the heat store of the body of the house and it's contents.
Also remember that you already have somewhere between 5-15 air changes per hour (ACH) unless in an actively well sealed modern Passiv house. At 5 ACH that's 12 minutes of continuous Lüften, 5 times per hour, so it is more like the 2p suggested.
The key element is to understand and appreciate when, why and how to do the Lüften to actively remove the 'warm damp (high absolute humidity) air' and swap it for cool dryer (low absolute humidity) air at a time when the differential is best and you already have your 'warm clothes' on.
I know that it's funny foreigner stuff practised for centuries (and we used to do it), but it's not a reason not to update mental models. It's the ill fitting mental models that are the major hindrance to warmer dryer homes.
so what is les expensive using a dehumidifier or reheating the house
I'd say using a dehumidifier is cheaper overall, but what do you do when you can't afford the upfront cost of a dehumidifier but suffer with condensation and mould?
@@GreenWhereItSuits Are you mental? You are advocating your ridiculous method up there ^, but recommending something entirely different here! "When you can't afford to buy a dessicant dehumidifier, pay for more gas, so then you definitely won't be able to afford a dehumidifier." You are 'green', as in naive and not very well informed.
I noticed in the comments a lot of people are worried about heat loss, this would be very low allowing moist air to leave the building over a short period, as there is still a lot of heat trapped within the building fabric and furniture.
Well explained and great illustration of RH. I use an online calculator to convert RH to Absolute Humidity so I can see grams of water per cubic meter of air. Thanks for a great video 👍
That means so much, thank you too!
Good content
Very informative explination on how humidity and condensation works. This may make sense in a cold climate, I don't think it works in a hot costal climate where during the day it is 30C+ at night it is 20C+. You will get some benefit, but the discomfort of that heat makes this impractical. Even if the same dynamics could work. Still just keeping your windows open obviously helps, but crime and other factors can make that not feasible either. I found a dehumidifier was just easier.
Yes Hot and Humid climates need a shift in when to do the exchange, assuming there is a point where it's advantageous. If Air Conditioning (AC) is common you are fighting a different enemy!
Excellent explanation!!
Great explanation pal, learnt a lot.
Learned how to waste your money!
@Humanity101-zp4sq How so?
@@gregcarnall9097 Read the other comments...
I live in northern Ireland,where average humidity outdoors (over a 12 month period) is 90% inside my house over 80% if I run a dehumidifier all night I collect around 10 litre water a night . Humidity may be down to 70-75%.i sleep even in winter with my window open ! Living in this shit hole is a nightmare! Rain and storm 300+ days a year
We live by a forest a mile from the sea and hover around 70% humidity, we don't have any mould anywhere because we keep the temperature in all rooms above the dew point. Simple.
We don't have mechanical extraction either.
Isn't it cheaper to just use a dehumidifier, the electrical cost of running contributes to heating the house, and also extract heat from the water vapour as it condenses on the dehumidifier coils instead of transferring the heat to the cold windows or worse out the window.
I have kept the single glazed metal frame window in the bathroom, It streams with condensation , which runs thro' the frame to outside, ( some times forming icicles ) , yes I loose 40w more heat than a double glaze window, & it is not as good as a £3000 MVHR , but that might have a 40w fan.
Having brick and plaster walls helps keep the house heat in the wall while the air is exchanged in the 5 minutes of Lüften.
If the house walls are low thermal capacity then the air-change will make for larger fluctuations in temperature (longer to re-warm and needing active heating).
I've done a "simplified Relative Humidity (RH) 'psychrometric' chart" (can be done in Excel) showing those constant 'water' lines across the RH-Temperature chart. The equations are in the "CIBSE CPD module 7 (2009)" (web search should find it).
Your house needs ventilation for other reasons than humidity BUT this method is not free. You are dumping all your heat. Get a dehumidifier! Because it gives out up to 50% more heat than the same electricity used in an electric heater. That is because the energy you had to use to boiling your kettle for example, to release the humidity, is returned as heat when you condens it out again.
They are also more effective for preventing damp and are great for drying clothes.
I agree it’s not free, however, you can minimise cost depending on when you do it. In the video I mention after dinner but if you do it before leaving for work, providing you have a south facing property the solar gain may offset some or all of the heat losses - depending on where you are and the makes up of your property.
you are only dumping the heat in the air . The majority of the buildings heat is in the walls. To raise 100m3 air by 10c needs 0.33Kwh of heat ... so a normal house heating outside air 1-3Kwh depending on temp etc ( is my maths right ?
@brackcycle9056 we must also add the lost latent heat of the moisture to the calculation. But an additional advantage is that dehumidifying is continuous and more comfortable. It also makes good battery top-up water.
i love how you say "fresh air" instead of "freezing air". this might be a good idea in germany, but britain has MUCH higher gas prices.
I mention doing this after lunch, but I practice it after we have showered in the morning which then allows solar gain to work on our south facing windows.
In a 2 bed semi would you have the dehumidifier upstairs or down stairs Thanks for any recommendation
I’ve thought upstairs works best as humid air rises, however, so does warm air. Perhaps my house has a warmer upstairs than downstairs as when I’ve trialled the dehumidifier in the downstairs hall it seems to capture more.
Great timely video...
Lol but if you dropped your house temperature to 5 to 7°c by opening all the windows to heat it back up to about 21°c would cost a lot more than running a dehumidifier to get rid of the extra moisture. 😂
Actually no, as soon as you shut the windows, the residual temperature rises rapidly in the dry air.
Tried this and can confirm it doesn’t work. To bring the humidity down from 85(!) after having windows open, I had to have heating on all night along with my industrial dehumidifier on at lowest setting. I’ll stick with keeping the windows shut and having my dehumidifier on all day as before - costs a lot less!!!
@@JamieW-o7b With your boiler on turbo maybe... Who's paying for the gas?
Dehumidifiers are very efficient there is no denying that. How do you propose lowering the internal humidity of the property WITHOUT a dehumidifier, which is the subject of the video?
If you perform this in the morning before going out for the day, solar gain will help introduce heat back into the property. If you are not in a detached property you will also gain some thermal benefit. That's without mentioning that the thermal makeup on the house will not have dropped to 7 degrees, and dryer air costs less to heat that humid air. Finally, at 5 degrees, you do not need to replace ALL of the air to benefit. As I mention in the video, fully saturated air at 10 degrees Celsius will significantly lower humidity levels when warmed to 19/21 degrees.
@@GreenWhereItSuits Its not possible! Dessicant dehumidifier cost £100. Payback time approx. two years.
PIV systems do the same thing and they are very affordable now.
+1 for PIV, got our main bedroom down from 75-85% to a steady 50%. The heating is definitely kicking in more but the house is mold free, have had a clear nose and no coughing for the first time in years so well worth it to me. If you're happy wiring a spur it's a pretty simple install too, about £400 in total for me
Positive ventilation without heat recovery will also be a waste of money in UK winter.
Repost since I missed one of AI many word swaps!
Got dehumidifiers running almost 24/7. In closed rooms with little use I'm still taking over 1 litre a day out. This way I'm drying down the room more than 10 mins + residual or whatever and avoiding having to reheat. I run meters too and the rate of rehumidifying is fierce! Faster than the rate of a 20 litre Meaco in one room can reduce it. Bearing in mind that size of unit is aimed at a small house, not one room. Your idea of good if the inherent dampness of the building is low. My dehumidifiers are slowly taking out less and less. Slowly!
You didn't mention about dew point. If the dew point outside is higher than inside then opening windows will make the humidy go up. The dew point is usually higher outside on really warm days and rainy days. I use my own personal weather station to give me local outside temperature and humidity readings that also gives me the dew point automatically. I can then use the inside temperature and humidy level to work out the inside dew point using a dew point calculator.
However I do feel that during the winter if you open your windows even if the dew point is lower outside then you are just wasting energy and have to heat up that air again and the cost of gas and electricity is high. I use a dehumidifier and it costs about 5p an hour and helps to dry the air that in turn the house heats up faster.
It is also safe to have a relative humidy level of 65% in your house. It is a bad advice that it has to be 60% or lower and scientific tests have proven this. Trust me I have never had trouble with mold or condensation or bed bugs and our house is old. 70% is where it gets too high.
It isn’t necessary to discuss the dew point but I appreciate that it would be of benefit for people to understand. At 06:10 I provide a guide that discusses an outside temperature of 9°C at 10°C at 100% relative humidity which is the same thing as the dew point.
I also have humidity in the high 60s and 70s without the use of dehumidifier and have only had issues (besides condensation) with mild in a previously unvented and unheated downstairs cupboard.
This video is aimed at those where humidity is causing issues and do not have a dehumidifier.
I appreciate the feedback you have given
dew point is a function of relative humidity.
1:40 I’m sorry but this is correct on paper but doesn’t correlate to real life. My room is 17 Celsius at 70% humidity… I put the fan heater on to increase the temperature and keep humidity the same but that’s certainly not what happened… the temp went from around 18 to 22 but the humidity sky rocketed to 80%. Look people it’s fcuking near impossible to lower humidity whilst raising the temp without a dehumidifier. Obviously there’s endless variables but in my experience, raising the temp always raises humidity. I mean I do have 4 fat plants in my room and have only ever tried to lower/raise humidity with plants in the room so can’t speak for plant less spaces.
Wish I would have seen this while I was in Germany. Crazy mold
How can you have lived in Germany and not known about Luften?
@ lived Wiesbaden for a year. Loved it but did not know I needed a dehumidifier
My appartment has MVHR but these systems are still not 100% efficient.
For an experiment I bought an efficient dehumidifier and turned off the MVHR.
So instead I now run the unit 4-6 hrs. a day to reduce humidity and prevent mold.
Always A LOT of water in the tank afterwards.
This way the enthalpy of condensation stays in the appartment.
So far it seems to work out as we have temperatures close to freezing for almost two weeks now and so far still don't turn on the heater ans have ~22°C inside.
With the MVHR running on the lowest setting I'd be running in the low 20s and Mrs. General be demanding to turn on the heated floors.
So far I'm happy but I'll keep monitoring the cost if it is worth it financially.
As I pay 11.5cents per kwh for district heating and 38cents per kwh for electricity.
After last night the device shut off after consuming 1.8kwh and there were almost 4l of water in the tank. Roughly measured 3.85l with 1l mugs.
Excellent advice, but have you ever heard the mainstream media tell people this clearly? Also, drier air is easier to heat, despite the heat you lost venting the house.
this is a good idea but it's not quite right. 100% humidity doesn't automatically equal condensation. condensation can happen at 10C, 17C or 24C - it depends on the dew point. Your point about cold air being drier is absolutely correct though.
In my example I discuss relative humidity by keeping the water content (vapour) static and alter the air temperature to increate and decrease the relative humidity. Eventually I reduce the temperature to a point where the water vapour in the air goes beyond 100% relative humidity (the dew point) and begins to condense.. That isn't to say that condensation occurs only at low temperatures. If you keep a room at any given temperature above freezing, and introduce more and more humidity, it will eventually reach a point where the air is fully saturated (100% relative humidity / the dew point) and with more moisture added you will see condensation form.
Interestingly, the dew point below freezing becomes the frost point.
Shock ventilation we know it as.
It's the 21st century, MVHR exists...
I think opening doors work better than windows because it cycles cold and warm air
The cost of heating the air is high. Why not just use a dehumidifier?
No it isn't. That is a myth. After I open my windows and then close them, the temp goes back up even with no heating on.
You must be living closer to the equator. Here in the UK where I am, it's 5 degrees C and the heaters need running several hours a day
@@cooliocrib4409 I am in the UK. According to the met its 10c where I am in the west mids but a bit windy.
Currently no heaters on and its 18.3c according to my CH thermostat. I opened the windows earlier and it went down to 17 for a bit.
Mid terrace council house built in the 1960s. Polystyrene balls in the cavity, about 250mm of insulation in most of the loft. There is a hole where the F and E and immersion used to be that I haven't got around to. Double glazing installed 15 years ago.
Had 8 air vents in the house originally (had a coal fire before) size of 2 house bricks each, now down to 5. Have those plastic covers but still let in air.
Heating kicks in of an evening usually.
Only 5 radiators in the whole house- only 1 in living room is a big 1200mm type 22 the others are type 11 and 800 x 600mm
Great explanation... but just get a decent size dehumidifier. If your house feels damp it will take around a month to dry out the walls of your home. Letting out all the heat every night is going to add significantly more to your energy bill than a dehumidifier running cost, and such a strategy is not going to be able to cope with the amount of moisture cooking and drying washing creates. I got one recently and it's made a huge improvement to our home's comfort.
Which brand/model did you opt for?
@GreenWhereItSuits initially got as 12L Daewoo unit but it felt a bit inadequate. Got an 18L Meaco Arete 2 instead (it's Costco's special version of the 20L) and have been really happy with it. It just stays on all the time and does its thing in the background.
Instead of using a dehumidifier, you are simply heating cold air and allowing what warm air is in your shelter to escape. That's not a very good solution in a cold climate, when heating is more expensive than a simple dehumidifier. Also, you are ignoring the high humidity in that cold air, (above 75% is great for letting black mold get into your house), then you warm it up (and the black mold grows and spreads). Water vapor is lighter than regular air (with about 55% relative humidity); if you do vent like this, open upstairs windows slightly, till the air cools, then shut them.
One of the big problems is that people live in apartments and houses with "open concepts" (fewer walls and doors). There are low humidity areas, (like living rooms, without water); and, there are high humidity areas, (bathrooms and kitchens, with lots of water). Cook in a kitchen, that is vented, not an open cooking area that allows moisture into the dining area and living room, (great smells, maybe, but high humidity going everywhere); put the washer and dryer into their own room or in the kitchen (not where they dampen the entire basement or near a hallway to spread the damp into the whole house); and, vent the bathrooms, (I'd leave a bathroom fan on 24/7 to vent an apartment), as a bath, shower, sink, and toilet produce more humidity than everything else in a house.
a Dehumidifier £1 a day to run 250 watts a fan 5p a day to run at 7watts a hour cleaner air less damp
Are you saying to run an extractor fan to remove moist air?
Tried this, and rh went from 62% to 60% after 30 mins - so, in the real world it doesn't work
What temperature was the 62% and 60% RH taken at? Did the temperature in the property drop at all during the 30 minutes?
Wet are is colder than Dry air at the same temperature.
Except it's the same temperature! Maybe you mean to say humid air has more specific heat capacity and higher thermal conductivity so can transfer heat away from something warmer more effectively.
@@TheGraemeEvans Wet air 'feels' colder than dry air at the same temperature is what I think he meant to say...
You know those little vents on your windows... Yeah this. If your happy just to vent heat and have to re heat your home, yes you can lower the humidity thos way. Much more energy efficient to use a dehumidifier though. Or if you want, a heat exchanging unit, the simplest i hve seen was built in to an in wall extractor fan that had in and out in one unit. Or have a proper system with full hvac / mvhr.
Can you give me an example of one of those simple units with in/out built into the wall extractor please.
Analogue thermometers and hygrometers are better than digital in most situations as they rarely fail and don't need batteries.
My in-laws have a beautiful analog hygrometer/thermometer! I believe digital ones still have their place, particularly being able to monitor the home remotely or even just making sure my children's bedrooms are comfortable without disturbing their sleep.
Modern digital hygrometers are cheap and reliable and plenty accurate enough. (pack of 5 for £13). What is missing is a "simplified Relative Humidity (RH) 'psychrometric' chart" (see my other comment for sources).
Without a suitable chart most folks don't know what to do with the magic numbers the hygrometers generate!
This is nonsense! Just advocating to remove warm air from your house (albeit potentially high humidity), replace it with cold (albeit drier) air and then reheat the air from scratch. Waste of energy heating, discarding and then reheating air. The most cost effective way to deal with high humidity is a dessicant dehumidifier. Low running cost, will remove excess moisture from air making it easier to heat and less humid. Unless you have heat recovery positive pressure ventilation, this idea is ridiculous. Best to insulate and draught proof as well as possible, rely on momentary door openings and trickle vents in windows to exchange fresh air, and manage humidity with a dessicant dehumidifier. Any other suggestion for comfortable cheap living at lower temperature where dewpoint can become problematic is just clickbait!
This video came about through hearing the stories of low-income households that are suffering with mould and do not have the financial means to purchase a dehumidifier outright. This approach will lower the humidity in their home. If they do this in the morning the property can benefit from solar gain, and if they are not a detached property they will receive some heat input from the surrounding properties.
For that reason, suggesting the use of a dehumidifier on a video that explains how to lower humidity without one is somewhat missing the point. I myself have a dehumidifier and it is very efficient, but we must be mindful that not everyone can afford such luxuries even if it costs less in the long run.
@@GreenWhereItSuits Totally missed the point....
I've totally rejected the desiccant humidifiers as they are generally one shot wonders pandering to those who aren't aware of their problems.
Another commenter notes how cheap it is to actually reheat the air (couple of pence). It's not a cost driver relative to comfort, mould, etc.
@@philipoakley5498 One shot wonders? You clearly haven't used a Meaco DD8L.
Cold air being drier depends upon where you live.
Humidity isn't a problem if the house is kept constantly warm, if you let it heat and cool again then you will have problems. We live close to a forest and the sea, our house is around 70% moisture in winter and we don't have any problems. This guy has no idea what he's talking about.
Humidity can still be a problem even if constantly warm. All you need it too many cooking pots without lids, too many showers, natural indoor clothes drying, too many people breathing, etc. Had a colleague with a rental property where the tenants, as a family, did karate/judo and washed their kit many times a week and let it drip dry, he ended up buying a high speed spin dryer for the laundry aspects!
Not true. If your house is hermetically sealed the moisture you generate from cooking, bathing, and sweating will have nowhere to go.
Nope.
The reason I’m here is because I need to lower the humidity from 70 to 45/50 WITHOUT lowering the temperature. I need it to be from 23-25 Celsius sitting at 45/50% humidity but I can’t afford a dehumidifier atm-.-