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Heating & Air Conditioning

Did oversized venting pipe kill our furnace?

11 years ago

I posted earlier this week about our 4 year old Carrier furnace problems. The first tech said we have a cracked heat exchanger. The second one, a certified Carrier man, told us the vent pipe extension is too big and caused soot to block the heat exchanger. He claims there is no crack, just bad blockage. The 2 inch pipe coming out of the furnace is connected to a 3 inch pipe. There is about a 12 foot run to the basement wall exit hole. Tech number two called Carrier and was told that the extension pipe should also be 2 inches if the pipe is less than 15 feet long. Both men say we need a new furnace. Would the wrong size pipe cause the furnace to stop working? My husband thinks that the installer or builder should be responsible for at least part of the replacement cost if the furnace quit due to improper installation. Any chance of that happening? Do we need a third opinion?

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Comments (5)

mike_home
11 years ago
I am skeptical about both your techs. I don't understand how a larger vent pipe can create soot and block the heat exchanger, and that if the pipe were 3 feet longer there would have been no problem. If you have a build up of soot, then you may have a chimney draft problem. I could be wrong, but I doubt the draft problem is being caused by the 3 inch diameter. My 40 gallon hot water heater has a 4 inch vent pipe!

If the heat exchanger is not cracked, then why is tech number two recommending a new furnance? Why can't vent pipe be fixed if that is the actual problem?

You should have the original contractor come in and review the installation. If as you say the installation did not follow Carrier's guidelines, then you have a good arguement about getting him to fund the repairs or replacement.
indygal
Original Author
11 years ago
The second tech said that if the furnace was vented through the roof, the 3 inch pipe would be fine. Ours is vented through the basement wall. There are several pages about venting pipe size in the manual and my husband is trying to figure out what should have been used. I guess the next step is having the installer come out. We really didn't want to use them as we've had several issues with other installation mistakes they made. We'll see what they say and then decide if we trust their installers enough to make this right.
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Thanks for your comments. Yesterday I tried to climb the roof that is at 45 degrees to seal the flashing. But I finally gave it up because it is too difficult to climb it. The shingles have sand. It is very slippery. I will call a roofer to handle it though it is probably not difficulty to fix the problem, sealing it because by further carefully check the top of the furnace pipe in the attic; I did see light through on one side. The water must drop from there. I can fix the problem but I am unable to climb the roof at 45 degrees. Though I will call the roofer, I would like to hear what good ideas you have to climb the roof. If one uses a Harness, he still needs to climb to the top of the roof and nail on it before he can use it, right?
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I agree with all the posters. That is the worse garbage install i've ever seen. I guess your code boys are just brain dead. Could be you have no codes. Your vent on the roof will NEVER draft properly in a million years, eat the shingles because of acid fumes,and could be a fire hazard. Even your gas pipe install is totally garbage and illegel. Tinmantu is dead on. No way in hell is that vent supposed to touch any combustable material. I guess you live in a no code zone and anything goes until 3 people are killed. If i did that install up here i'd be out of business, my licence pulled, sued, and probably in jail. That includes the gas piping. I feel for you. We were told in school that the U.S watches our codes. We set most of your gas and electric codes. Just takes you guys years to catch up and i think you need three code related deaths before there is a change, might be five. Can't remember. Bottom line is if your home was in Canada with that install the house would be locked off untill all code infractions were repaired and the installers were jailed or out of business. Well not jailed but out of business or forced back to school with a major fine. Here is how it works up here. I make one mistake with venting or gas i pay $150.00 for a new inspection. Make another mistake on the same home i pay $500.00 for the inspection. I make a third mistake on the same home i lose my licence and have to go back to school and pay a $1000.00 fine. As i said before, i feel for you. You want to know what a gas code or electic code is, come up here. I can't believe most of you people are still alive. Is this a conspiracy on their part ? Canada is an elected dictatorship but our codes protect people. Can't say the same for the entier U.S. Some states have it right on. Some haven't a clue. Just one man's opinion.
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Are the BTU numbers you listed input or output values? Do you know the make and model numbers of your furnaces? The right way to do this would be to look up the allowable PVC diameters and lengths in the installation instruction for your furnaces. You should find a chart that shows the range of allowed sizes. The dimensions are a function of altitude, diameter, length, and number of 90 degree elbows. If the PVC is being rerouted you have to confirm the maximum length and number of 90 degree elbows are allowed. The 2 inch diameter should be fine. In general even 100K BTU furnaces may be able to use a 2 inch PVC pipe if the length is short with a few 90 degree turns. You just have to make sure it is allowed. I don't see the need to ever get bigger furnaces, and likely your next furnaces will be smaller and more efficient.
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The vapor that comes from our propane fueled furnace is quite acidic which might be one reason that yours might damage the metal of the generator. Ours runs year-round since it is the hot water (runs both the hot water and the heat for the house). I am not sure if it's the heat or the acidity, but it does kill the grass by the vent pipe (~3' stretch) as well as having damaged the cementaceous siding that was nearby. If I were you, I would dig up a chunk from the side of the shrub to transplant as well as trying to start cuttings so that hopefully one or the other survives. Depending on your fuel and how the vapor dissipates, it may or may not kill the hydrangea, but I am fairly sure that it will damage it.
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tigerdunes
11 years ago
Agree with Mike...sounds very fishy...
indygal
Original Author
11 years ago
Not only would the vent pipe need to be redone, but the heat exchanger would have to be replaced as it is supposedly plugged up with soot. I think they cost almost $900. I don't think it would be a good idea to put over $1,000 into a furnace that might break down again any time. Other parts could be damaged from the excess heat. The work that needs to be done would void what warranty we have. We're hoping to get the company that installed it to come look at it on Monday.
THN3363
11 years ago
Did your venting get resolved? little late but always interesting. I am a Mechanical Contractor in Florida and provide training to contractors within this state for both private and public entities......
Todd

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