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Heater vent - double or single wall?

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6.6K views 13 replies 3 participants last post by  supers05  
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#1 ·
I will try and explain my setup, then the questions.
  • I have a gas furnace in my basement.
  • Coming out the top of the heater appears to be a 4 inch single wall pipe.
  • There is a water heater about two feet away with what appears to be a 3 in pipe that joins into the 4 inch.
  • There is about a 3 feet run, maybe 45 degrees and the 4 inch pipe goes vertical into a 5 inch double wall pipe.
  • The 5 inch double wall runs through two floors into my attic, from there I think it expands to either 6 or 8 inch single wall. So, probably 24 feet straight vertical.
  • That single wall in the attic runs at about a 45 degree angle maybe 6 or 8 feet and then goes vertical through my roof. (I do need to check the attic configuration as it has been a few months since I have been up there)
About a year ago, I had an issue in the attic where I had a failure, so lots of moisture came down and now I need to replace the run in the basement. The attic section was built back exactly how it was originally built.
The company that originally installed the heater is suggesting to me that I need to replace all the pipe with double wall. But, they really haven't given me a definitive explanation of this. I have my doubts for the following reasons
  • My house, before I bought it, was owned by a home builder and he really didn't cut corners on anything. He was known for doing things the right way. I just kind of trust the design that has been in place for nearly 30 years.
  • My current system was installed by the same company that is currently given me this advice. If they are so sure my system needs double wall (I think this means it would be category 3), then I question why it wasn't built that way when they installed this current system about 11 years ago.
So, my questions are
  • Based on what I have described, do I really need double wall? If so, does it need to be all the way through the house?
  • How can I tell if my system is Category 1 vs Category 3?
Many thanks in advance for the advice.
 
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#3 ·
Can you help me out and explain a little bit because right now I am getting some conflicting information. I have another source telling me that since I have much more than 6 inches clearance in both the basement and attic that I can use single wall.

I am not necessarily opposed to going double wall. It is just when I look at my local Menards, they have most of the B-vent that I need except for a 3 in to 5 in WYE, and that seems hard to find.
 
5
#4 ·
The flue gases in the single wall pipe through the attic will condense rotting out the pipe, especially if it increases in size as it goes through the attic. You don't need to run b vent from the furnace and water heater to the basement 5" b vent as long as you maintain 6" clearance to combustibles with the single wall pipe. Use a 5/4/3 EZ vent to make the connection to the b vent in the basement. Do not use single wall up through the house and attic.

Image
 
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#6 · (Edited)
57TinkerMan said:
The flue gases in the single wall pipe through the attic will condense rotting out the pipe, especially if it increases in size as it goes through the attic. You don't need to run b vent from the furnace and water heater to the basement 5" b vent as long as you maintain 6" clearance to combustibles with the single wall pipe. Use a 5/4/3 EZ vent to make the connection to the b vent in the basement. Do not use single wall up through the house and attic.

View attachment 713862
Click to expand...
Thanks for the info.

I seem to be stuck on not finding the B-Vent Wye that I need, plus some of the length runs in the basement seem fairly non-standard, like 33 inches, or 44 inches. So, I am going to have to do some customizing. Also the b-vent to water heater hood seems like something I can't find. It is available in 4 inch, but not 3.

What I have available local is Amerivent, and I am pretty sure the DW coming through the ceiling isn't compatible. If I put an adaptor on there, it lowers my sloop by about 4 inches. I haven't measure exactly, but I am guessing I have about a 7 foot run from water heater to the basement ceiling. And maybe between 2 foot and 3 foot rise.

I did create a sketch of the basement, which I am attaching. The current config has the water heater vent joining around the middle of the basement run. The distance from water heater to the Wye is around 4 feet, and then a little less than 3 feet to the double wall coming through the floor.
Image
 
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#10 ·
90,000 is for the furnace only. Water Heater is 40,000. The furnace does have a fan on the vent pipe right where the vent pipe leaves the furnace.

Still struggling to find local available parts, even in singe wall. I am seeing 30 gauge galvanized at Lowes that look like I can make the configuration I need. But, unclear if 30 gauge is sufficient enough for the basement run.
 
#13 · (Edited)
davesconzeuntry said:
90,000 is for the furnace only. Water Heater is 40,000. The furnace does have a fan on the vent pipe right where the vent pipe leaves the furnace.

Still struggling to find local available parts, even in singe wall. I am seeing 30 gauge galvanized at Lowes that look like I can make the configuration I need. But, unclear if 30 gauge is sufficient enough for the basement run.
Click to expand...
You need to use 24 gauge, minimum. The 3" is a bit on the small side for the hot water heater. (you need a 3ft rise before the common vent) I would recommend a 4" connector. The furnace is fine at 4". The common vent needs to be 5" B vent the whole way.
 
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