Positive and Negative Pressure In Your Home
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- Опубликовано: 10 янв 2023
- In this video we’re talking about building pressure, specifically what can cause your house to be under
negative or positive pressure. We also discuss how you can check whether your house is positive or
negative, and some things you can do to fix issues with your house’s pressure.
Items mentioned in video:
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#HVACdesign, #ProCalcs #loadcalcs, #Energycalcs, #ductlayout, #manualD, #manudalJ, #manualS, #hotcoldspots, #positive and negative pressure
This was a super interesting video. I live in South Florida and the heat has been brutal on the AC it is not feeling great at the peak of the day. If we have a 95 degree day it's going to be a bad day inside but it it drops to 92 to 93 its a world of difference. Thanks for the video your explanations were spot on I plan on sharing this video and I want an energy inspection.
Glad you loved the video! We're pleased to hear that you found it helpful and accurate. Living in South sounds like quite the challenge with the intense heat and if you're considering an energy inspection, that's a fantastic step toward optimizing your living environment and potential saving on energy cost too!
We finished out our attic and just ran new ducts. Since then our master bedroom has been getting warm. Walking out of our bedroom you can feel actual conditioned air. I am thinking we screwed up so contacted hvac company. They said possible negative pressure, and offered the only solution of adding return in my finished attic. I kept the door open for days and it never solved the problem.
There could be a few things causing the issue, it's hard to say without more details. It's possible that your system is undersized now since adding the additional conditioned space of the finished attic, unless you had a load calc done to check. It also sounds like the master bedroom may not be getting enough air now, and if the supply grille in the master bedroom is the wrong size for the amount of air, that can cause issues with hot spots. A return in the finished attic would be recommended though either way, and per most codes is required when a room is occupiable and has a door that can be closed, like a bedroom or office. It would probably be a good idea to have a load calc done, as well as the duct system evaluated to try to pinpoint the issue. If you'd like to discuss further, feel free to send me an email at dana@procalcs.net.
-Dana, ProCalcs LLC
Found your video to be very educational. I came here is seeking an answer as to why the vents on left side of my house are displacing cold air from the vents when the furnace is off. It is 2 degrees or more colder on this side of the house (office). When the room is heated, the office feels cold after the furnace goes off in 4-5 minutes, or sooner, depending on how cold it is outside. I suspect the warm left over air in the cold vent is mixing. This is resulting in cool air dropping down from the vent which requires I wear a jacket and my fingers and hands are cold, although the thermostat says it is 71 and a local temperature gouge in my office saying it is 69.
I tried your negative test and I even more confused. Yes, when opening the door on the left side of the house, cold air came through the crack of the door. However, when I slightly opened the door on the right side of the house, which feels warmer and more comfortable, the air flow was double, if not triple, the amount of cold air coming through the door crack. I will say the stairs to the 2nd floor are just beyond the right front door, so I suppose the argument it is sucking cold air in and going straight upstairs. However, the 2nd floor is very comfortable and warm at 71 degrees. Either way, both doors indicate I have negative pressure.
I believe strongly the house HVAC ducts were installed poorly (looks like spaghetti and you cannot even get to ducts to check), they are not sized correctly with 10ft ceilings and very little air flow out of the vents such that a 6ft person standing directly under the vent cannot even feel the heat hitting their head when the furnace is on. No luck with HVAC companies as they are looking for easy fixes (replace heating unit with larger system, move system from 3rd floor to crawl space, etc.). I am not sure they are schooled in how to address negative pressure homes. Not sure where to go from here.
Hi Michael! It sounds like it definitely is possible you have an issue with negative pressure causing some temperature problems. But since you mentioned the temperature difference between upstairs and downstairs, it could also be due to the location of the thermostat if there is only one. If the thermostat is upstairs, it's possible the system is only running until the upstairs reaches temperature, but that isn't enough time for the downstairs to warm up enough. Since warm air rises, the upstairs will always be a bit warmer than downstairs. This is why we always recommend having a zoned system, with a separate thermostat on each floor. Of course I don't know your exact setup or equipment, but it is something else you can look into.
Your videos are great and I have concern about what my HVAC company is wanting to do while installing a new system.
They are wanting to run a dehumidifier with the intake, pulling air from outside that is filtered and dumping it into the Plenum before the filter.
This is to get fresh air into the house and also create a positive pressure.
1 live in south Louisiana and pulling air without the dehumidifier would be putting
90% humidity into the Plenum.
Your advice is greatly appreciated.
Hey there! We appreciate your kind words and we're thrilled to hear that you enjoy our videos! 😊
Your concern about your HVAC company's proposed installation is valid, and it's important to ensure that any modifications to your HVAC system are both effective and safe.
Here are my thoughts:
Given that you live in south Louisiana with high humidity levels, controlling indoor humidity is crucial for comfort and preventing mold and moisture-related issues. If your system was not designed to have outside air added before, you'll want to have a load calc completed to make sure the system can handle the additional hot air and humidity. And also, it's always a good idea to get multiple opinions from different HVAC professionals. Have another reputable HVAC company evaluate your home and provide recommendations. This can help you compare different approaches and determine which one is best suited to your specific needs.
Hi there! We'd be happy to help with your HVAC concerns. Please feel free to email us at tom@procalcs.net along with your address. We'll do our best to assist you with any questions. 😊
By chance I just discovered a very dangerous negative pressure condition in my home. Hot and humid weather this past week so we closed all windows and doors, ran 2 portable air conditioners venting to the outside. Add an electric dryer that runs a lot....etc etc Today I cleaned my oil boiler and thanks to some left over crud when I fired it back up I saw smoke entering the room through the closed damper. No big deal right. I just missed vacuuming some dirt in the fire chamber. The next time the boiler fired it did the same thing. The damper was never pulled open while the boiler was firing. I pushed it open to make sure it wasn't stuck and it immediately closed back up. I opened a window to help exhaust the smoke and a wind hit me in the face. There was no wind outside but the negative pressure pulled so much air in the window you swore it was windy outside. I opened a second window and the same thing. I left the windows open and observed the boiler the next time it fired and the damper opened and no smoke or smell entered the room. I will be adding some sort of ventilation in the mechanical room soon. Thanks for the videos!
Wow thanks for sharing that, that was interesting.
Would house humidity go up if you increase positive or negative house pressure? Our humidity went up when we increased size of our return duct and we don’t know why. We think we have negative pressure but when barometric pressure drops in evening humidity goes down we are perplexed
Hello, @moreglistrefine1432 thanks for your comment! Normally, higher positive pressure pushes out humid air, reducing indoor humidity, while negative pressure can draw in outside humid air, increasing indoor humidity. In your case, the larger return duct could make the house negative and might be affecting airflow, potentially drawing in more outside humid air.
Hello, just watched your video and found it to be super informative and interesting. Just bought a house built in 1990 it has a 4 ton Ac and heating unit all in one. Located on the roof. I installed a one piece dog door that mounts on to the tracks of my sliding glass door. And when the air conditioner comes on the flap of the dog door pushes out and stays open. Is this what your calling a positive air flow? And what do you recommend I do to decrease this air flow so the flap stops blowing out and sending all that cool air outside? Help !! Please!!
Hello Jorge! We're glad you found our video informative and interesting! It looks like when the dog door is being pushed out, the pressure inside is higher. For homes, we want to have a slight positive pressure as that's better than negative.
Here are some steps you can take to address this issue:
1. Inspect the seals and gaskets around your sliding glass door to ensure they are in good condition and not allowing air to escape. If they are damaged or worn out, consider replacing them to improve the overall insulation of your door.
2. Many dog doors come with adjustable settings to control the sensitivity of the flap. Check the user manual or product documentation for your specific dog door to see if you can adjust it to require more force to open. This might prevent it from being pushed open by the air pressure.
3. If you're into DIY, you may also place a magnet on the sides of dog door to create a better seal and minimize the amount of air escaping.
It would also be best to have a professional come out and inspect the system. Hope this helps!
Interesting video! Would a local air conditioning unit (not central ducts) that is taking air from just that room and spitting it back into that room, create positive pressure for that room?
Because there is very little to no duct work, and supply and return are in one room, the duct work has a very small chance of adding to the negative of positive pressure in the room, but it could happen. However, depending on how tight or lose the room is to the outside, there could easily be a negative pressure. A lot depends on the type of system and how everything is installed and designed.
Your videos are great and I have concern about what my HVAC company is wantingv to do while installing a new system.
They are wanting to run a dehumidifier with the intake, pulling air from outside that is filtered and dumping it into the Plenum before the filter.
This is to get fresh air into the house and also create a positive pressure.
I live in south Louisiana and pulling air without the dehumidifier would be putting 90% humidity into the Plenum .
Your advice is greatly appreciated.
So, everyone has negative pressure pulling in outside air (from the fireplace in my case) when an exhaust fan is turned on. Do you have a solution? I had to seal up the house to pass the air test done by the county. Now the exhaust fans pull from the flu in the fireplace (I don't close it because we have fires all the time). I open a window when the dryer is on but want to know if you have a better solution.
Hello @ryanl6722! Thank you for your comment. It sounds like you're dealing with a challenging situation. Could you please share the results of your blower door test and the size of your house? Typically, since exhaust fans are intermittent and have a smaller CFM compared to the total volume of the house, the pressure differential created by them isn't usually a big concern. It primarily increases infiltration. Regarding the air coming in through the fireplace, closing the flue might help, but it could redirect air through other openings.
great video. i live in a condo 2BD 2BA approximately 1000sqft and it has it's own HVAC system (inside my unit), washer and dryer hooked up to some duct by entrance door, kitchen range fan, bathroom fan, 3 windows that open for each room (master bedroom, living room, and spare room), along with a patio door opposite of the main entrance. Because we are the 3rd floor out of 4 floors, i would assume the washer and dryer duct is centralized but i do believe our HVAC is internal and no other ducting to and from other floors or at least from what I've gathered.
I currently have negative air pressure utilizing your method of closing everything and opening the main entry door a crack, which determined air coming in and not out. How do i create positive air pressure within this environment??
Forgot to mention, because it's a condo, my front door is within a corridor with doors on opposing ends that open to outside air.
Also, thanks for your time!
Hello, thank you for your comment! Given your current situation of having negative air pressure in your condo, ensure that your windows, doors, and any other openings are well-sealed to prevent air from escaping, which can help maintain the positive pressure you create. Also, try to limit or adjust the use of bathroom and kitchen fans, as they pull air out of the condo and increase negative pressure. Additionally, appliances like dryers and kitchen hoods that exhaust large volumes of air typically need makeup air to prevent significant negative pressure inside when they are in use.
@@procalcsuniversity1484 excellent thank you. anything I can buy like an erv or some kind of device to put in the window?
@@TecraTube Yes, an ERV can also help manage the air pressure in your condo. However, we highly suggest having your condo inspected first by professionals to assess your specific needs and recommend the best product for your situation.😊
Question: I have a newer constructed house and I noticed that I get headaches when the heat is on only in the master bedroom. Sometimes the pressure closes the door. All bedrooms are on the second floor. So the master is on one side of the house, the remaining 3 are on the other side. Fyi...the other rooms are always colder than the master room. Does that mean it is a negative pressure and the exaust setup is incorrect?
Hello @ccroney00
Thank you for your comment. It is possible that the negative air pressure in homes potentially causes headaches, although it's not a direct or universal effect. Headaches can result from various factors related to indoor air quality and comfort, which can be influenced by negative pressure.
In your case, if the master bedroom consistently feels warmer while the other bedrooms are colder, it could indicate that there's an imbalance in the airflow within your home. This could be due to problems with the ventilation system, such as inadequate exhaust or improper distribution of air.
It would be best to have a professional come out and inspect your system. It could be that the room, in particular, has higher pressure than the rest of the house because it does not have a return, or the supply is putting too much air.
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Apologies the link isn't working. By pen, do you mean a smoke pen? If so, heres a link you can use: amzn.to/3HsM1y1