Troubleshoot hi eff gas furnace venting
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- Опубликовано: 2 окт 2013
- This one covers failures related to venting installation of high efficiency gas furnaces.
This video is part of the heating and cooling series of training videos made to accompany my websites: www.graycoolingman.com and www.grayfurnaceman.com to pass on what I have learned in many years of service and repair. If you have suggestions or comments they are welcome.
If you are a homeowner looking to repair your own appliance, understand that the voltages can be lethal, the fuels are highly flammable and high pressures are used. Know your limits. 
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You are a genius!!! I've been having problems with my pressure switch. I looked and checked everything and still have trouble. I think it's the hard 90's. I will replace them with sweeps.
Yorbinfo is so valued to me, thanks a lot to take time to do this video, I almost quit, but finally i fix my preassure switch problems.
Thanks for the support.
GFM
valuable concept, thank you...
Probably most areas will require it eventually, but the installation methods as far as ells and level are the same. Thanks for the comment.
GFM
Great information. Thanks for posting.
also, how should the pipes ultimately LOOK on the outside of the house? Meaning...what is the BEST lengths for each of the PVC pipes and how should they be positioned? We had a HE furnace installed and we arent happy with a few things. We have a serious dust issue now...and I JUST noticed that the LEFT side pipe coming out of the furnace is NOT even securely joined to the extension pipe!
Thanks . God bless you .
If you are an engineer 40 or older that designs fittings, that is a sweep 90. Another great video
That particular sweep 90 is also a street ell rather than a standard elbow, the difference being that a standard elbow has two female ends while a street ell has one female and one male.
Question, GFM if you have time. I’m a new tech (installed for a couple years, been doing service work for about a year) I work with guys who say these exhaust vents sweat on the outside if you don’t have them insulated. But to me it doesn’t add up that “warm liquid on inside + cold air outside = condensation on outside.” Condensation always forms on the other side of “cold” in my experience. Never had a cup of coffee sweat. I’ve yet to see this happen and I’ve worked on many 90+ furnaces with uninsulated vents. Admittedly, it could be that I just haven’t been around long enough to see this, and I’m definitely new enough to be missing something and I’ve been wrong many times! But none of these dudes can tell me why it supposedly sweats on the outside. Can you speak to this?
thank you...
Thanks
GFM
great info. Please tell me...do BOTH of the PVC pipes that come up and out of the furnace have to pitch back towards the furnace?Thankyou.
Yes
GFM
Good Video.
How about using a condensation tee with a clear flexible hose to the nearest drain or floor drain. Plus you can only go a certain amount of feet before it goes outside there is limit on piping and elbows. I living in nyc have seen during cold winters the outside fitting for exhaust freeze over due to condensate build up of ice in 20 to 25 f degree temps. Try getting to that fitting on 4th floor of a building. The unit which was Teledyne Heatmaker were notorious for this but they did have a safety switch that shut the unit down after cycling three times. I feel thru trial and error will catch up to solve these issues but I hate be the one to be the example.
I also live in a cold winter area. I have never seen a freeze up of a vent that did not have a screen in it. Not saying it cannot happen, but a condensate drain should not be necessary if the venting is pitched toward the appliance.
Possibly if the venting is in an unconditioned space, it could be insulated as I have done sometimes.
GFM
Thanks.
GFM
Thank you for the video. I am having an issue with my two year old 96% with flame “hiccup” or fluttering. So far we have replaced the board’ pressure switch, as well as the gas valve. The flame flutters intermittently and sometimes shuts the furnace down. I have several sweeps for a 25 ft run on the vent side. Toward the furnace, it seems that a have a spot that it slightly sloped away from the furnace. I am still within installation spec for the run and elbows @2 inch. Three HVAC guys including a family member said they have no idea what is going on. Question is, can this slight dip (6”) in the pipe possibly be messing with the pressure switch? It makes each time it calls for heat. Just sputters slightly a few minutes into the cycle. No apparent HE issues as the flame is blue and consistent through the cycle.
I am literally at a loss with this unit at the moment, this video kind of gives me a last hope.
If you have a 6" dip, that is your problem. The unit may drain mostly back to the furnace during the off cycle, then when condensate collects in the dip during the on cycle, it makes waves that will partially block the vent.
GFM
Moving more air faster seems like a no-brainer, but if the added resistance of the short els helps keep the hot air in the heat exchanger a slightly longer period of time, could that perhaps help boost efficiency?
Modern furnaces have gotten this so dialed in that any efficiency change will be so small as to be meaningless. Just buy one less latte a year.
GFM
I have a mold issue in the attic,backside of decking.Attic venting & circulation are correct.looked for all /any interior leakage to attic leaks,nothing,what i'm suspecting is the furnace exhaust blowing heated air in the winter up & into an eve vent which is almost directly over the exhaust & pretty much what looks to be the origin area of mold in the attic,a similar home 3 doors down brought the exhaust piping vertical & higher than the house,is there something to this ?
It could be. The exhaust gas is 100% humidity. Can you send pics?
GFM
I have some how do I get them to you ?
Tjfreak Send them to grayfurnaceman@gmail.com
GFM
grayfurnaceman Great vid and critically important information, this is good info in relation to HE Furnaces but there are vented units which are not HE and require the vents to be sloped away from the furnaces due to their inability to handle condensate, only thing that is confusing is the vent, exhaust and intake, spacing on the exterior of the dwelling. Any pointers?
Just curious... can I use my basement inside air for combustion on the newer 90+ furnaces instead of running a pipe for outside air? My basement is 1000 sq ft and 8ft tall.
On most furnaces, yes. I would check the install manual.
GFM
You would create a negative air pressure environment in your basement if you vented your intake in the basement. This is dangerous, especially if your hot water heater relies on atmospheric venting.
I am experiencing excessive moisture in my venting in a wet basement. The exhaust pipe exiting the furnace sags at the outlet side of furnace and pools water running into the furnace. This pooling of water causes excess moisture in my vacuum lines. Should I just redo the vent piping because what is iinstalled is glued and can only be adjusted oh so slightly. We just had new ac condenser/Acoil installed and had to move furnace 2 inches. Now the furnace is non functioning again with condensate in exhust vent. American standard horizontal mount. Condensate is supposed to run BACK into furnace right? With the exhaust vent going up the vent pipe could be filled with water. I'll have to double check all drain weep holes for plugging and consider any advice. Tia.
I would replace everything it takes to get rid of the sag.
Condensate should run to the furnace, just not in copious amounts that a sag would sag.
GFM
There are 2 tubes in the picture - is the 2nd tube for "intake"?
See GFM's next video:
ruclips.net/video/PAbHBa00UjE/видео.html
I have an Arcoaire high efficiency downdraft furnace in a slab home. The exhaust gases are vented outside but the furnace intake is from inside the house in a very active hallway with a lot of dust in the area. Would it be better to pull air from outside with 2" pipe and if so how far away from the exhaust pipe be from the intake? My inducer blower only lasts two years because of all of the dust and dirt from the hall and that's why I'd like to go to outside air.
With a gas furnace running, during a drought, what would cause moisture to come back down through a vent pipe and puddle under the unit? (This vent is fed with a liner up through a chimney and connected to a vented gas chimney cap.)
Drought has nothing to do with moisture from combustion gasses. The moisture is from the burning of the gas. There are several reasons this could happen. If the liner has corroded, the leaking vent gasses may condensate in the chimney. The furnace could be under fired. The liner could have been disconnected. I would first check the bottom of the vent between the furnace and the chimney. If it is rusted out, there is condensation in the vent. Hope this helps.
GFM
Thanks, the pipe is definitely rusted. The moisture is coming from inside the piping and down through the furnace.
You will probably have to replace the venting. If it is single wall, it will have to be replaced with either Z flex or B-vent.
GFM
Hi thanks for the video. I was wondering if you can help me. I have someone wanting to sell me something I don't think I need. Earlier this year I extended my 2 inch id gas heater exhaust pipe out to 35 feet it was 25 feet. I did this to vent the fumes away from where we sit on the deck. I made a mistake when extending it because I did not use enough support straps and it developed a low spot in the pvc pipe which resulted in condensation that got stuck in that low spot and it probably froze or had water built up, causing my furnace to overheat. I fixed the slope , no low spots the water drained out right now and the slope is right. I think I am good, but the Hvac company told me that my 2 inch intake and output should not be placed under deck. In addition, they told me that I needed to increase 2 inch Id pipe to a 3d ID pipe. . Do you know if they are telling me the truth when they say it should not be under the deck and that I need a 3 inch pipe to go 35 feet. I think since I fixed the slope issue that I might be good with the 2 inch id ran 35 feet?
Furnaces come with installation instructions, mine is a 137pg PDF. It lists the max length and elbows. Based on my tables, 35ft is nothing unless you have 6 or more 90s in the pipe.
Has your furnace worked since you fixed the slope? If you're near the limit, maybe leave the intake pipe short (unextended) and keep the exhaust long. But like this video says, Read The F Manual :)
Have a video on power vent water heater into type B? I see you have a cat 1 venting rules but power vent water heater isn't classified type 1. So I just tried it yesterday and it worked fine. There'll be just as much condensation as my gravity water heater so what's the big deal? Why should I have to convert to 2" PVC? So I got the power vent water heater as my backup to my gravity water heater but I don't think I will run them at the same time because they are two different categories, unless you do think I can and the power draft won't blow out the pilot on the gravity? Have you seen anything like that before-- the power vent water heater actually snuffed out the pilot light on the gravity water heater if they are both vented together? Please make a video?
I could make a video but it would consist of "Don't do it". You will corrode the B-vent. It is not designed for condensation. If I came upon this setup I would be required to red tag it. Not just because it does not follow code but it is dangerous.
GFM
@@grayfurnaceman, that would be great. Fails are also learning experience. Next Q: Can you ridge the PVC, say halfway or wherever, so that condensation drains out as well as back in? Condensation can't drain out because it potentially freezes in layers each freezing day and that would block vent at the output?
@@1weirddoe571 If you want it to drain out, pitch toward the vent. Then armaflex the vent to stop freezing. Rheem requires armaflex.
GFM
@@grayfurnaceman, expensive, stainless steel, single wall z-flex for Cat1-4 could do it? But not Centrotherm since can't be used for bvent Cat1, right? ruclips.net/video/aKPMeVSaLqk/видео.html
and if it can take high temps then why not use for b-vent replace: ruclips.net/video/H3I3sxgS6Xo/видео.html
GFM,
when calculating diameter of pvc pipe do you add total piping/elbows of intake and exhaust or just exhaust? thanks
Depends on manufacturer instructions. All manufacturers have their own system.
GFM
Does air intake pipe has to be pitched back toward furnace?
Yes.
GFM
Why?
So any moisture that gets into the pipe can be directed to the drain system of the furnace.
GFM
Thanks you.
The white ell is considered a vent ell not short radius code would not allows us to use that sharp of a ell. Vent ell as in Plumbing.
Hello. Can anyone help me with my furnace? The problem I'm having is air is blowing back pass the combustion blower from the vent after it cycles or the system is turned off. The furnace work great except that one little thing. Is the combustion motor bad or is something else going on? I'm sure that is where my problem is coming from because when I take the vent air line off, not air flows back through the vents in the house.
Are you saying you are getting outside air into the heat vents? If outside air is coming back thru into the combustion chamber it will not go into the heat vents unless you have a massive crack in the heat exchanger. I would have a professional look at it.
GFM
grayfurnaceman yes I am and think you. Is that something I can change out or repaired myself or do the whole unit need replaced?
James Richardson It kind of bothers me that outside air is being mixed with air in the duct. Is it possible you have an outside air inlet duct? The reason I have said go to a professional is you may have a simple problem that does not mean a heat exchanger.
GFM
Why would the manufacturer care what kind of elbow you use, as long as the total resistance is acceptable? AirQuest just specifies the maximum number of equivalent feet, and you deduct from the maximum linear feet according to the number, angle, and radius of elbows used.
Some manufacturers determine the resistance of even one short radius ell, when used with the minimum vent length of vent pipe is too much resistance.
GFM
It's not hard to apply the primer without letting it run down the pipe. I can't stand sloppy primer work.
patbhvac1 Yea, it isn’t BBQ Sauce, in which case then you want to slop it on thick,lol.
We have to use system 636, abs and pvc has been banned.
System 636
They're not called swept 90s they are called long radius 90 s. The only fitting that has the word swept in it swept tee.
Ted Price TomAto, Tomaato
GFM
grayfurnaceman lol I am a new jersey union refrigeration tech. We just love to bust balls on piping ling go sorry i could not resist.
Some manufacturer's manuals call it "long swept".
First sentence he said *acrost* ...
Bye bye.
Looks like , not nice