Intake Pipe Condensation 95%


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Old 12-24-13, 07:17 AM
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Intake Pipe Condensation 95%

95% furance. The exhaust and intake are 2" pvc and run next to each other and exits my basement at the sill plate.

On the coldest days, about 2 ft. of the makeup air pipe where its about to exit the basement is condensing on the outside.

The exhaust next to it is dry. THere is a supply duct next to both pipes as well. Outside there is no condensation/ice on the makeup but there is very little ice acumulation on the exhaust.

Its an unfinished basement so a little bit of drippage on the cement floor is not a big deal but I was thinking over time it could damage the sill plate.

Why is condensation happening? And how should I rectify this?

Ide be happy to answer any questions you might have to get a better picture of what I am trying to describe.
 
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Old 12-24-13, 07:27 AM
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you need to check the furnace manufacturers recomendations on how the piping should be run,especially the exhaust. there are a maximum number of ells or 45's allowed. the pipiing should slope back towards the furnace to allow proper drainage. maximum distance of piping. also,they should show on a drawing where the exhaust and intake are located on the putside. they give very specific dimensions on this.
 
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Old 12-24-13, 07:35 AM
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you need to check the furnace manufacturers recomendations on how the piping should be run,especially the exhaust. there are a maximum number of ells or 45's allowed. the pipiing should slope back towards the furnace to allow proper drainage. maximum distance of piping. also,they should show on a drawing where the exhaust and intake are located on the putside. they give very specific dimensions on this.
THis all checks out, its not the issue. This is on the outside of the intake pipe in the basement btw.
 
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Old 12-24-13, 07:36 AM
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The condensation is caused by the pipe, drawing in cold outside air, being cooled below the dew point of the surrounding air. A concentric vent is the best cure for this sort of problem but replacing a 2 pipe with a concentric would leave a hole in the sill plate. You could try insulating the intake & sill plate. Another solution might be to run a dehumidifier in the basement.
 
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Old 12-24-13, 07:40 AM
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Grady- Thats exactly what I was thinking. I was going to stuff insulation around the pipes exiting the sill plate but I was leary for a few reasons.

1. is there any harm with the insulation touching the exhaust pipe?
2. would insulating the outside of the pipe cause condesation to acumulate inside the pipe?

I dont want to add insulation and by doing so cutting off the intake air ie: ice it up.

THe other idea I had was to use that black foam stuff you se on hot water pipes... if they make it in 2" size?

Adding a concentric vent is not going to be possible for a number of reasons.

Thanks
 
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Old 12-24-13, 07:48 AM
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seems you have the answer already...so why ask....you are never supposed to insulate the pipe outside.
if it was installed according to manufactuer...you wouldn't have this problem....
it has to be in same pressure zone?
not a great idea for insulation on or near exhaust
good luck...................
 
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Old 12-24-13, 08:10 AM
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Pressure zone? Please elaborate.

Also insulation around a condensing furance exhaust is likely no issue... why is it not a great idea may I ask? (and to clarify in case you missed this, this a condensing furnace... pvc not a bvent).
 
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Old 12-24-13, 08:18 AM
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I wouldn't hesitate to insulate the intake. It shoudn't cause condensation on the inside since the air coming in is drier than that in the basement. Insulation near or even in contact with the exhaust will hurt nothing. Many times the vent pipes go thru an insulated wall.

The "pressure zone" refers to a side of the house. The intake & exhaust need to go out the same side of the house. On a windy day one has high pressure on the windward side & low pressure on the leeward.
 
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Old 12-24-13, 09:06 AM
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Grady, Seebee or anyone else....

Do you think I should just use a piece of fiberglass batting and stuff it into the crevice betweent he sillplate and the floor joist. Or should I use something like that black foam stuff with the split side that is usally seen on water heater hot pipes? Or seebee (I respect your opinion too) nothing at all?

I was thinking the exterior of the intake pipe is condensing because its in close proximity to the warm exhaust or a supply duct that is close by. I dont think the basement is "humid" persay...

FWIW I only see this occuring when outside temp is getting to about zero.
 
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Old 12-24-13, 09:10 AM
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I would start with the fiberglass in the cavity. If that doesn't help, move to the foam on the pipe itself. You can get self stick foam pipe wrap. Finding preformed foam for 2" PVC could be tough.
 
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Old 12-24-13, 09:19 AM
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Rheem has specs for insulating both intake and exhaust in cold attic situations.
 
 

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