pvc flue outlet/pipe

[inphx]

I am contemplating flying to mom's house and replacing her two gas furnace. The replacement i sourced has two PVC pipe outlets one for combustion air (optional) and one for the flue outlet (required). If i need to connect to decades old metal flue i assume i can find an adapter to do it right, however i will be under a time constraint to complete - is the PVC pipe used for the flue some special plastic? Its not electrical conduit?

 

[404]

Short answer, I do not know.

Long answer, at one time there was a special plastic flue pipe, it all failed, giant recall and cluster fark.

If you tell us the model, or provide a link to the install sheet, we can speculate more.

 

[brewchief]

Pvc vents on furnaces cannot be connected to any type of metal vents.

Sent from my XT1254 using Tapatalk

 

[e36jon]

Your (Or moms area) codes may not allow PVC for the vent pipe, or the neato concentric vent + intake. In San Francisco I have to vent with metal (even though the output from the newer furnaces is lukewarm at best) and can't do the concentric thing.

The gas furnaces I have been looking at (All high efficiency types) say just regular PVC for the vent is OK.

Disclaimer: Not a pro, and didn't even sleep at a Holiday Inn Express...

 

[Stuart in MN]

Generally, high efficiency furnaces with PVC air intake and exhaust vent right out the side wall, they don't get connected to existing chimneys.

 

[rlitman]

Pvc vents on furnaces cannot be connected to any type of metal vents.

That is not true, however the acceptable metals are on a very small list (forget aluminum, or typical stainless).

Anyway, to the OP, expect to make new holes in the structure for new PVC vents. Forget about trying to use the existing flue.

Oh, and be warned that cellular core PVC (what is commonly found at the box stores in larger PVC sizes) is not acceptable for venting. You will probably have to go to a plumbing supply for your PVC.

 

[larry4406]

Hi efficiency furnaces (90+%) discharge at low temperatures below the dew point. They are also known as condensing furnaces. The condensate is mildly acidic. For this reason and the low temperatures, metal flues are not used. The exhaust and intake pipes are both sloped at 1/4" per foot backwards to the furnace where you then route the condensate to a floor drain or a condensate pump.

To my knowledge not possible to connect to an existing metal B-vent.

Using the combustion air piping improves efficiency by using unheated outside air.

 

[laser3kw]

My HVAC guy installed a new high efficiency furnace last year. He did not connect the PVC vent to the old metal vent, BUT he did use the old vent and ran the PVC up thru it and sealed it with a boot where it exits the metal and makes its turn about. PVC all the way from furnace to termination outside.
PS - mine is a condensation type furnace. Be aware that you have to provide a drain for the discharge from the unit. I had to install a pump to lift it to the nearest drain (I had no floor drains available).

 

[zmaxmotorsports]

Pvc vents on furnaces cannot be connected to any type of metal vents.

Sent from my XT1254 using Tapatalk

 

[zmaxmotorsports]

That is not true, however the acceptable metals are on a very small list (forget aluminum, or typical stainless).

Anyway, to the OP, expect to make new holes in the structure for new PVC vents. Forget about trying to use the existing flue.

Oh, and be warned that cellular core PVC (what is commonly found at the box stores in larger PVC sizes) is not acceptable for venting. You will probably have to go to a plumbing supply for your PVC.

Ive never seen a 90 plus furnace connected to a metal chimney.Ive used solid core schedule 40 for venting power vented chimneys for a long time.

 

[inphx]

Thanks for all the tips. I had no idea PVC was widely used in new units for vents.

This site had some interesting reading and explanation why the exhaust is under UL purveyance.

 

[rharman]

As others have noted, PVC is fine for a 90+ unit. The original install of mine had the special pipe that was recalled. I missed the recall cutoff by about a year - could have had a whole new vent system at $00.00 - dang.

I was skeptical about the PVC but researched it. No problems whatsoever. Added a condensate pump to lift it up into the overflow drain.

 

[dlfiene]

If the units are up in an attic with the potential of freezing temps. I would recommend you run a heat tape specific for drain line and insulate per heat tape instructions. Or go with a furnace that is not 90 plus eff.

When I had my new house built they put the furnace up in the attic. First year everything was fine as we had a mild winter. Second winter drain line froze solid and shut the furnace down, builder came cut out old drain replaced entire line and put some cheap insulation on it. Well the third year it got even colder and froze solid and busted in the attic while I was at work. Furnace continued to run. Well those things can produce a lot of water. My ceiling was ruined, carpet soaked and the builder warranty no longer any good. So I replaced the drain line and put heat tape as well as insulation on the drain pipe. No problems since I did that.

 

[larry4406]

Years ago the builder I work for used to put 90+ units in unconditioned attics. We ensured that the length of the drain in the attic was not more than 12" (i.e., went straight down into the attic truss bay and then thru the home to the basement floor drain), the drain was heat taped in the attic and was fully insulated.

To my knowledge none of our installations froze.

Regarding PVC, you need Schedule 40 not the foam core as was noted by others.

 

[dlfiene]

I went with schedule 40 when I replaced mine.
However mine is a single story home and has a 25 foot run in the attic to make it to the nearest drain. So that all got heat taped and insulated with inch and half thick armaflex for the whole run. Little over kill but I was fed up with the problem!

 

[brewchief]

Foam core can be used on some brands, you need to sit down and carefully read the install instructions to know for sure. Install instructions will also have a chart showing min and max length as well as how many fittings can be used and what is acceptable for the vent terminations.


DIY furnace install isn't real common but can turn out OK if it is well planned out. Spend some time reading the install manual ahead of time.

 

[Showkey]

Not sure where this problem with cellular PVC comes from quote from install manual......

"The use of Schedule 40 PVC or ABS cellular core (Foam Core) plastic pipe is also acceptable as a flue/vent and intake pipe material. PVC primer meeting ASTM F656 and PVC solvent cement meeting ASTM D2564 specifications must be used. Fittings must be DWV type fittings meeting ASTM D2665 and ASTM D3311. Carefully follow the manufactures instructions for cutting, cleaning and solvent cementing of PVC.
For Canadian installations; all PVC pipe, fittings and joining materials must be UL S636 listed.
As an alternative to PVC pipe, primer, solvent cement, and fittings, ABS materials which are in compliance with the following specifications may be used. Two-or-three-inch ABS Schedule 40 pipe must meet ASTM D1527 and, if used in Canada, must be CSA listed. Solvent cement for ABS to ABS joints must meet ASTM D2235 and, if used in Canada, must be CSA listed. The solvent cement forthePVCtoABStransitionjointmustmeetASTMD3138. FittingsmustbeDWVtypefittingsmeetingASTMD2661andASTMD3311 and, if used in Canada, must be CSA listed. Carefully follow the manufacturers’ instructions for cutting, cleaning, and solvent cementing PVC and/or ABS."

Link to full install manual

http://www.the-wholesale-warehouse.com/ebay/pdf/goodman/GMSS96_Installation.pdf

 

[cowboyjosh]

If the units are up in an attic with the potential of freezing temps. I would recommend you run a heat tape specific for drain line and insulate per heat tape instructions. Or go with a furnace that is not 90 plus eff.

When I had my new house built they put the furnace up in the attic. First year everything was fine as we had a mild winter. Second winter drain line froze solid and shut the furnace down, builder came cut out old drain replaced entire line and put some cheap insulation on it. Well the third year it got even colder and froze solid and busted in the attic while I was at work. Furnace continued to run. Well those things can produce a lot of water. My ceiling was ruined, carpet soaked and the builder warranty no longer any good. So I replaced the drain line and put heat tape as well as insulation on the drain pipe. No problems since I did that.

As a builder, I hate, hate, hate furnaces in attics for this reason. For energy code now everything is high efficiency. If I have a bonus room over the garage I will build an insulated furnace closet in a heated garage below the bonus room. On some massive 2 story homes I have put furnaces in attics and have had a couple of the drains freeze. Heat tape was not an "acceptable" means of preventing it from freezing in our AHJ and we got dinged on one final for having it in place. Aside from freezing, furnaces in attics are a pain in the *** to install during construction, service, and eventually replace. Also with an attic furnace, although its a remote possibility, its something else to potentially cause a fire. On homes with attic furnaces, I always install a heat alarm tied into the smoke alarms or a heat alarm tied into the alarm panel in the event of a furnace fire in the attic.

 

[dlfiene]

As a builder, I hate, hate, hate furnaces in attics for this reason. For energy code now everything is high efficiency. If I have a bonus room over the garage I will build an insulated furnace closet in a heated garage below the bonus room. On some massive 2 story homes I have put furnaces in attics and have had a couple of the drains freeze. Heat tape was not an "acceptable" means of preventing it from freezing in our AHJ and we got dinged on one final for having it in place. Aside from freezing, furnaces in attics are a pain in the *** to install during construction, service, and eventually replace. Also with an attic furnace, although its a remote possibility, its something else to potentially cause a fire. On homes with attic furnaces, I always install a heat alarm tied into the smoke alarms or a heat alarm tied into the alarm panel in the event of a furnace fire in the attic.

Yeah I absolutely hate them up there too!
It worries me if I ever sell the house what an inspector will say about the heat tape. If I had a spot to relocate to the garage I would, but these houses are not that spacious.

 

[larry4406]

As a builder, I hate, hate, hate furnaces in attics for this reason. For energy code now everything is high efficiency. If I have a bonus room over the garage I will build an insulated furnace closet in a heated garage below the bonus room. On some massive 2 story homes I have put furnaces in attics and have had a couple of the drains freeze. Heat tape was not an "acceptable" means of preventing it from freezing in our AHJ and we got dinged on one final for having it in place. Aside from freezing, furnaces in attics are a pain in the *** to install during construction, service, and eventually replace. Also with an attic furnace, although its a remote possibility, its something else to potentially cause a fire. On homes with attic furnaces, I always install a heat alarm tied into the smoke alarms or a heat alarm tied into the alarm panel in the event of a furnace fire in the attic.

I agree completely. The company I work with changed our designs and now both of our 2 zone 90+ systems are in the basement. We use 14" engineered floor joists with coordinated cutouts and the ductwork for the 2nd floor is in the 2nd deck so our systems are 100% inside the thermal envelope.

 

[zmaxmotorsports]

As a builder, I hate, hate, hate furnaces in attics for this reason. For energy code now everything is high efficiency. If I have a bonus room over the garage I will build an insulated furnace closet in a heated garage below the bonus room. On some massive 2 story homes I have put furnaces in attics and have had a couple of the drains freeze. Heat tape was not an "acceptable" means of preventing it from freezing in our AHJ and we got dinged on one final for having it in place. Aside from freezing, furnaces in attics are a pain in the *** to install during construction, service, and eventually replace. Also with an attic furnace, although its a remote possibility, its something else to potentially cause a fire. On homes with attic furnaces, I always install a heat alarm tied into the smoke alarms or a heat alarm tied into the alarm panel in the event of a furnace fire in the attic.

 

[deckmonkey]

Not sure where this problem with cellular PVC comes from quote from install manual......

"The use of Schedule 40 PVC or ABS cellular core (Foam Core) plastic pipe is also acceptable as a flue/vent and intake pipe material. PVC primer meeting ASTM F656 and PVC solvent cement meeting ASTM D2564 specifications must be used. Fittings must be DWV type fittings meeting ASTM D2665 and ASTM D3311. Carefully follow the manufactures instructions for cutting, cleaning and solvent cementing of PVC.
For Canadian installations; all PVC pipe, fittings and joining materials must be UL S636 listed.
As an alternative to PVC pipe, primer, solvent cement, and fittings, ABS materials which are in compliance with the following specifications may be used. Two-or-three-inch ABS Schedule 40 pipe must meet ASTM D1527 and, if used in Canada, must be CSA listed. Solvent cement for ABS to ABS joints must meet ASTM D2235 and, if used in Canada, must be CSA listed. The solvent cement forthePVCtoABStransitionjointmustmeetASTMD3138. FittingsmustbeDWVtypefittingsmeetingASTMD2661andASTMD3311 and, if used in Canada, must be CSA listed. Carefully follow the manufacturers’ instructions for cutting, cleaning, and solvent cementing PVC and/or ABS."

Link to full install manual

http://www.the-wholesale-warehouse.com/ebay/pdf/goodman/GMSS96_Installation.pdf

The problem with piping is on the exhaust, intake can be abs if wanted because it doesn't heat up. Abs was allowed on the exhaust before but it cracks and must be replaced now. Also depending on temp you might have to use cpvc instead. Might only apply to boilers though. Read the manual for venting that comes with the unit it's pretty easy to run. Hacksaw, glue and maybe a tape measure.

 

[dreasoner]

I much prefer using concentric vent terminations. They look much better than a two pipe install and the exhaust keeps the intake from freezing up. What is everybody else's take on this?

 

[inphx]

Thanks for all your input - i found 84% efficiency units local in town that used the old metal exhaust and it was an easy swap. The supplier was helpful to convert my cardboard sheet metal mockups to artwork making it look pro.

 

[deckmonkey]

I much prefer using concentric vent terminations. They look much better than a two pipe install and the exhaust keeps the intake from freezing up. What is everybody else's take on this?

I use concentric if possible, two pipes usually look like you spent most of the day huffing the glue. Because of space I had to go with 2 separate 3" vents and the intake frosts up once in awhile if it's windy. It's a pain because it's at a rental and I have to remember and check it before they call and say the heat isn't working at 2 am.

 

[Norcal]

Around here attic mounted furnaces are about the only type used in new tract homes, slab floors & no basements mean limited choices where to place them, so packaged units or the garage is just about the only other choice when plan with tract homes is cheap, cheap, cheap. Years ago there was a big recall on one make of attic mounted furnace, they went out of business.

 

[6768rogues]

We use schedule 40 white PVC piping all the way to the vent terminal. It is the same pipe used for drain, waste and vent.

 

[padroo]

I know about the furnace not working at 2AM in the morning. I see others call it frost up but mine were choked off with ice shutting down the furnace. I built the house and installed the furnace and it always happened on the coldest nights of the year. All I did was install a PVC coupling and another piece of pipe to make one pipe longer than the other and that fixed it.