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Old 12-21-2010, 06:05 PM   #1
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Why might current PVC pipe be unusable for replacement furnace?


We have a high-efficiency furnace with a cracked heat exchanger, so we're buying a new one. We had 4 contractors come out and give bids. Only 1 of the 4 said that the current 3" PVC pipes cannot be used with the replacement furnace/AC. He didn't say why. He said that the pipes would need to be 2" and he'd have them moved closer to the furnace, which would require making another 2 holes in the house (we already have 2 where the PVC pipes currently are). Further he said that removing/replacing the existing pipes might require cutting the drywall of the finished basement room next to the furnace.

The other 3 contractors all said that the 3" pipe could be used without a problem and would not put any more holes in the house or need to cut drywall. All 4 are considered good contractors in the area.

So are 2" pipes necessary or better for air flow? I'm trying to discern why his view is so different than the others. His estimate requires more labor but is close in price to the others' estimates. For the record, he proposed Carrier Performance 95% furnace and 17-SEER AC that would qualify for the tax credits.

Thanks for any information/insight.

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Old 12-21-2010, 06:22 PM   #2
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Why might current PVC pipe be unusable for replacement furnace?


What size in BTU's is he quoting. The piping MUST match the manufacturers specs and Carrier does not use as large of piping as Rheem, Goodman, Armstrong and others so he may be correct. If he did a heat load calc and found your house needs a smaller furnace and is correctly getting you the proper furnace he may have to use 2" pipe. For a few bucks you should do your own heat loss calc
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Old 12-21-2010, 06:38 PM   #3
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Why might current PVC pipe be unusable for replacement furnace?


Sorry I forgot that part. We're replacing a 1992 Carrier 90%, 88,000 btu unit and a 1994 York 2-ton AC.
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Old 12-21-2010, 06:41 PM   #4
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Why might current PVC pipe be unusable for replacement furnace?


What size is he quoting, post the model # and I can lookup the venting 4U.
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Old 12-21-2010, 06:45 PM   #5
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Why might current PVC pipe be unusable for replacement furnace?


Wow--thanks for the help. He gave me an informal quote in an email, but based on the information in that quote, I figured that he's referring to a Carrier Performance Furnace: 2-stage 58HDV080 (80,000/56,000) (95%) and Performance AC: 2-ton 24APA7 Performance™ 17.
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Old 12-21-2010, 07:01 PM   #6
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Why might current PVC pipe be unusable for replacement furnace?


3" shouldn't be a problem on that furnace.

Ask the contractor WHY it can be reused. If he can't give a reason. Then there is none.
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Old 12-21-2010, 07:02 PM   #7
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Why might current PVC pipe be unusable for replacement furnace?


I don't have the newest model info but looked up a regular 80,000 and it uses either 2" or 2.5" in very long runs so I think he is right and following their specs. A 90,000 Lennox uses 3" and your old unit was so close to 90,000 it needed 3". W/O doing a heat loss calc he may be undersizing the unit for your house or the other 3 guys may be oversizing depending on what units they are quoting. You are on the borderline 80,000 = 2 inch, 90,000 = 3 inch in a lot of different manufacturers and models. Carriers can be finicky (the older than 6 yrs old ones) and don't like oversized pipe. Had to put restrictor plates in the intake of some as there was flame liftoff from the burners problems. Also needed a minimum 15 feet of pipe.
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Last edited by yuri; 12-21-2010 at 07:04 PM.
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Old 12-21-2010, 07:20 PM   #8
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Why might current PVC pipe be unusable for replacement furnace?


Quote:
Originally Posted by Vaandjay
We have a high-efficiency furnace with a cracked heat exchanger, so we're buying a new one. We had 4 contractors come out and give bids. Only 1 of the 4 said that the current 3" PVC pipes cannot be used with the replacement furnace/AC. He didn't say why. He said that the pipes would need to be 2" and he'd have them moved closer to the furnace, which would require making another 2 holes in the house (we already have 2 where the PVC pipes currently are). Further he said that removing/replacing the existing pipes might require cutting the drywall of the finished basement room next to the furnace.

The other 3 contractors all said that the 3" pipe could be used without a problem and would not put any more holes in the house or need to cut drywall. All 4 are considered good contractors in the area.

So are 2" pipes necessary or better for air flow? I'm trying to discern why his view is so different than the others. His estimate requires more labor but is close in price to the others' estimates. For the record, he proposed Carrier Performance 95% furnace and 17-SEER AC that would qualify for the tax credits.

Thanks for any information/insight.
Tax credits are great u should say I want a permit and would like the results. Yes it's me Hix heat 1
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Old 12-21-2010, 07:27 PM   #9
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Why might current PVC pipe be unusable for replacement furnace?


Quote:
Originally Posted by yuri
What size in BTU's is he quoting. The piping MUST match the manufacturers specs and Carrier does not use as large of piping as Rheem, Goodman, Armstrong and others so he may be correct. If he did a heat load calc and found your house needs a smaller furnace and is correctly getting you the proper furnace he may have to use 2" pipe. For a few bucks you should do your own heat loss calc
Load Calculator
Wht is a btu
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Old 12-21-2010, 07:31 PM   #10
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Why might current PVC pipe be unusable for replacement furnace?


Quote:
Originally Posted by Hixheat1 View Post
Wht is a btu
Didn't yuri post a link about BTUs in another thread for you.
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Old 12-21-2010, 07:43 PM   #11
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Why might current PVC pipe be unusable for replacement furnace?


Quote:
Originally Posted by beenthere

Didn't yuri post a link about BTUs in another thread for you.
I would ask wht, would happen if we used three inch pipe versus two it maybe two much combustion air. Just asking. If we had to much combustion air wht would happen.
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Old 12-21-2010, 07:49 PM   #12
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Why might current PVC pipe be unusable for replacement furnace?


Improper ignition, too much draft in the burner box, flames lifting off the burners AND flame sensor and causing lockout. Noisy burner, bad combustion. Bigger is not always better.
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Old 12-21-2010, 07:56 PM   #13
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Why might current PVC pipe be unusable for replacement furnace?


Quote:
Originally Posted by yuri
Improper ignition, too much draft in the burner box, flames lifting off the burners AND flame sensor and causing lockout. Noisy burner, bad combustion. Bigger is not always better.
I think, the guy with the smaller unit did his job. Now the question did he do a load calc. Or is he just a or a p . Your write the noise sucks. And no savings
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Old 12-21-2010, 07:57 PM   #14
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Why might current PVC pipe be unusable for replacement furnace?


I assume you're joking about my lack of knowledge, and that's fine. Nevertheless, due to the cracked heat exchanger on our existing 1992 high-efficiency furnace, it makes sense to replace it with a 95% because the tax credit essentially makes the 95% the same price or less than the 90%. It's not like I'd be tricking anyone if I didn't mention the tax credit, though I could have lied and said I used mine already to see how much less a quote would have been. Admittedly, they bring up the tax credit thing, and I don't like that they may give different quotes based on someone's tax credit situation, but I'm sure it happens. Still, for some reason, I never thought about lying until your message.
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Old 12-21-2010, 08:05 PM   #15
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Why might current PVC pipe be unusable for replacement furnace?


Quote:
Originally Posted by Vaandjay
I assume you're joking about my lack of knowledge, and that's fine. Nevertheless, due to the cracked heat exchanger on our existing 1992 high-efficiency furnace, it makes sense to replace it with a 95% because the tax credit essentially makes the 95% the same price or less than the 90%. It's not like I'd be tricking anyone if I didn't mention the tax credit, though I could have lied and said I used mine already to see how much less a quote would have been. Admittedly, they bring up the tax credit thing, and I don't like that they may give different quotes based on someone's tax credit situation, but I'm sure it happens. Still, for some reason, I never thought about lying until your message.
Look I would like to say sorry. I'm a trane dealer can't say anything but want u to have a good install. A load calc. Is a must. Usually if u go by price alone u loose think before u make your choice.

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