13

A contractor just finished installation of new HVAC system with a category 1 furnace (model: GMES800805CNAA).

He originally used a reducer to connect 4 inch exhaust to a 2 inch PVC pipe. He claimed that he has done so in the past and it worked well. After we started the new unit, we ran into some issues and eventually ended up with a completely melted PVC pipe. He replaced first few ft of the exhaust with a metal 4 inch pipe, but terminated it with a PVC 4 inch to 2 inch reducer and let it vent through the wall.

His claims that PVC melted because it is summer, and during winter pipes will be completely fine.

Is it safe to use a PVC 4 to 2 inch reducer and PVC pipe venting to the side of my house?

replacing melted pvc: enter image description here

finished product: enter image description here

Dimi
  • 255
  • 3
  • 9
  • 8
    Come on. Is this a joke post? – jay613 Sep 09 '21 at 14:41
  • 13
    Take pictures and contact your state licensing board. And don't let this person in your house EVER again, not even to "correct" things. Get someone competent to do it. – Doktor J Sep 09 '21 at 15:04
  • 7
    And make sure the "contractor" pays the costs - a lawsuit would be a turkey shoot with this degree of shocking negligence. You'll need a real chimney installed and that will add to the costs. Why are you buying an 80% furnace in 2021 anyway? The cost of installing the chimney will probably eat up the difference between a 95% furnace (which you **could** use PVC for), and you'll end up with lower heating bills and a lower carbon footprint. – J... Sep 09 '21 at 16:50
  • For anyone that hasn't looked into newer high-efficiency furnaces, they have additional heat exchangers and actually do vent their exhaust gas via 2-3" PVC pipe, but the air temperature tops out around 120F and is perfectly safe. As was mentioned in the post, older style furnaces vent the hot exhaust directly without cooling, and it's easily hot enough to melt plastic. – JPhi1618 Sep 10 '21 at 20:59

2 Answers2

29

HELL NO

Whichever joker is installing an 80% furnace with a PVC pipe for the exhaust needs their license revoked pronto, because that's a patent CO hazard. Non-condensing appliances operate at flue temperatures well above the safe working temperatures of PVC or any other plastic, and thus need to be vented using a metal B-vent. (Conversely, condensing appliances generate corrosive condensate that will eat ordinary B-vent alive. Stainless steel double-wall can be used as a "universal vent", and is what you're supposed to use on condensing appliances as per UL listings, but the condensing gas appliance manufacturers haven't quite gotten the memo incorporated into their install manuals yet.)

ThreePhaseEel
  • 79,142
  • 28
  • 127
  • 220
  • Thank you for the quick response. If he replaces 2inch PVC pipe segment with a metal pipe (not sure if 2inch metal pipes exist), will it be OK? It will still be 4inch pipe reduced to 2 inches for about 8ft, and exhausted through the side of the house. Or is getting higher efficiency furnace the only option for horizontal ventilation? – Dimi Sep 09 '21 at 04:23
  • @Dimi I doubt it. My understanding of the American system is that "Category I" means natural gravity venting (exhaust getting sucked out of the furnace by the stack effect of the flue), which is completely incompatible with horizontal runs (no stack effect there). The kind where an exhaust blower creates positive pressure in the exhaust that pushes it out through the vent is called "Category III". Here in Europe we also have standalone exhaust fans that you can install at the beginning of the horizontal run to sort of turn Category I into Category III, no idea if such a thing exists in the US. – TooTea Sep 09 '21 at 06:55
  • @Dimi A quick google gave me [Tjernlund HS1 Gas Sidewall Power Venter Fan](https://www.amazon.com/Tjernlund-HS1-Sidewall-Power-Venter/dp/B000CDAOFG) (no endorsement of either the product or the retailer). That looks like what I had in mind, no idea about the legality/code requirements. – TooTea Sep 09 '21 at 07:05
  • @TooTea thank you for your response. It looks like power venter might work in theory, but its use is discouraged by manufacturer of my 'new furnace' and NFPA. Is replacing my existing system with a high efficiency furnace without combustion air intake the only option then? ( question here https://diy.stackexchange.com/questions/234480/running-high-efficiency-furnace-without-outside-air-intake ) – Dimi Sep 09 '21 at 07:07
  • 5
    pvc-NO..1. A reducer is a no-no. Creates back pressure and is not allowed 2. You cannot run the exhaust horizontal it must slope upwards.( quarter-inch per foot) 3.Safety Controls i) A fan proving switch that prevents the heater from operating if the power vent used to operate the side wall vent is not working ii) A timer control that keeps the power vent operating for a period after the burner has stopped, typically for 45 seconds, to purge remaining combustion gases from the heating appliance NB Safety controls and power vents for gas fired heating appliances are certified by the AGA, – Brad Sep 09 '21 at 11:02
  • 2
    @Dimi -- I'd be seriously considering ditching gas heat altogether, especially if you can tighten up the house (air seal/insulate/weatherize) while you're at it – ThreePhaseEel Sep 09 '21 at 11:33
  • 6
    If you are unable to install a traditional metal flue in the way it's supposed to be installed, if you HAVE to use long horizontal runs or PVC, then you HAVE to install a suitable boiler, not the one you have. You should get rid of this contractor. He should be in jail. "It melted because it's summer" really sounds like something from a Monty Python plumber. I'm hoping to hear this is all a joke. But if not, don't let this person back in your house. (I have seen power vented high temp flues, but they are rare and you really have to know what you're doing. And they are not plastic.) – jay613 Sep 09 '21 at 14:46
  • 1
    @jay613 unfortunately, this is not a joke... Contractor said that he "asked around shop, and everyone was installing 80 percent units with PVC pipes for ages and never had any issues". Should I call some kind of licensing agency or a fire department to have them check all of his and his shop's previous installations? Living in Knox county, TN – Dimi Sep 09 '21 at 17:02
  • 1
    @Dimi Yeah, that sounds like a class-action suit just waiting to happen... blood from a stone, though, but at least those guys need to be stopped if they're doing this everywhere! – J... Sep 09 '21 at 17:19
  • 1
    IDK who you should call but if you want to take it on yourself to prevent this person from installing death traps, and possibly find some that he's already installed, it wouldn't be a bad thing. He obviously isn't pulling permits and having inspections, so you'll have trouble finding records of his work. He probably isn't licensed. IDK what body could compel him to hand over his records, if he even has any. – jay613 Sep 09 '21 at 17:25
  • 1
    @jay613 Could just call the police and report them for installing without a licence - let the cops sort it out. – J... Sep 09 '21 at 17:27
  • 13
    Update: Not sure if one of the agencies that I reported him to reached out to him, or if one of his 'colleagues' was an actual certified HVAC technician, but contractor completely changed his tune and went from "I already did all the work. Contract is done. I cannot return unit. If you want new one you have to pay me for new unit and full re-installation costs" to "Just pay me the difference for high efficiency furnace and one that you have, I will replace it for free.". Thanks everyone for giving me courage and information I needed. Y'all might have just saved my life. Will post updates. – Dimi Sep 09 '21 at 19:54
  • @Dimi do not let this person into your home again. they already tried to kill you twice. get a licensed contractor to do the replacement. your life isn’t worth the few thousand bucks you would save by letting him do the “replacement.” if he screwed this up so bad, what else did he screw up? – Jacob Krall Sep 10 '21 at 16:50
  • 4
    @JacobKrall I have hired a local HVAC professional to advise me on this matter. He said that the best course of action for my wallet is to have that 'contractor' replace 80% unit with 96% one (I will only pay the difference in cost of those units) and have an HVAC/Code professional thoroughly examine his work to make sure everything is good. Furnace is being replaced right now. Gas valve will remain in OFF position until all work is inspected by a 3rd party. – Dimi Sep 10 '21 at 17:05
  • 1
    @Dimi that sounds reasonable! I’m glad you have a professional to advise you – Jacob Krall Sep 10 '21 at 17:55
6

Are you sure that contractor is not secretly a hitman? I give him props for creativity, that's for sure!

On a serious note, furnaces with efficiency of less than 90% must be vented via metal pipe above your roof line. The exhaust is hot and extremely gaseous. You don't want the gases creeping into your house through your eaves/soffit nor an open window/door. You also don't want someone standing next to it because it can burn them.

His claims that PVC melted because it is summer, and during winter pipes will be completely fine.

Why are you running the furnace during the summer? Regardless, PVC should not exist anywhere in your furnace's exhaust system, period.

MonkeyZeus
  • 15,488
  • 2
  • 21
  • 57
  • 2
    We powered furnace on to make sure it is working. Flame was going out after 15 seconds and entire house was smelling like gas. Fun all around. While it is still summer, temperatures do get somewhat cold at night and require occasional 15-20 minute bursts of heating to keep temperature comfortable. – Dimi Sep 09 '21 at 13:03
  • 7
    @Dimi Wow, I'm sorry that you're in this fiasco. That contractor does not sound qualified to install furnaces and it could kill your family in the middle of winter. I suggest getting a real HVAC contractor but I do understand that money might be tight. – MonkeyZeus Sep 09 '21 at 13:15
  • 1
    @MonkeyZeus The lawsuit against PVC guy might pay for it. – chrylis -cautiouslyoptimistic- Sep 09 '21 at 15:06
  • @chrylis-cautiouslyoptimistic- lawsuit will cost more than cost of current 'ticking timebomb' and new HVAC system together. – Dimi Sep 09 '21 at 15:12
  • @chrylis-cautiouslyoptimistic- Unless you're a lawyer or can get one to work pro-bono for you then there isn't much of a case here. No one was hurt and there is still time to do things right. If OP lets the install proceed with PVC at this point then this question can be used against them in court to counter-sue with a fraud case. – MonkeyZeus Sep 09 '21 at 15:16
  • @Dimi If you're somewhere cold enough that you need a furnace in the first week of September during the nights then an 80% furnace is probably illegal already. 30 States banned anything less than 90% **eight years ago**. Hell, I'm way up in Canada and I'm not even turning the furnace on yet at all. So either you're somewhere that's pretty darned cold or your house has shockingly bad insulation. You'd save yourself a fortune by improving your insulation. – J... Sep 09 '21 at 17:00
  • @J... ... or Dimi is just someone whose comfort temperature is on the very high end of the bell curve. – Dan Is Fiddling By Firelight Sep 10 '21 at 11:54