air intake for hi efficiency furnance


Old 12-10-07, 12:41 PM
skydiverMN's Avatar
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Join Date: Dec 2007
Location: Minneapolis
Posts: 84
air intake for hi efficiency furnance

I have an insulated plastic tube that's feeding outside air into my basement (sits in an empty 5gal bucket). I assume that this is combustion air for the furnance. My intake sorkel for my furnance is about 6" long and curved down, and it just ends there. My home isn't new and this furnance install is a replacement model to what existed before. Because the plastic breather tube was already there I assume that it was easier for the contractor to use this vs. run a new line (laziness?). In a perfect world shouldn't this be hooked up directly to the outside as this is far more efficient than just having cold air pouring into my basement? Plus it's seriously cold in the basement too, but probably only in part to the outside air.

Should I think about running PVC to the outside? I know that there's a minimum distance requirement to the exhaust tube, but I don't know this for sure.
How is this tube usually vented to the outside? Would I just need to hook up some PVC and punch a hole in the sill plate (or whatever the 'on edge' piece is called), but how is this usually made 'pretty' for the outside? We have vinyl siding and for the other entry points they've always used some kind of putty, etc. What do you recommend?

Thanks for your help!

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Old 12-10-07, 12:45 PM
skydiverMN's Avatar
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Join Date: Dec 2007
Location: Minneapolis
Posts: 84
Talking what about the hot water heater....

I forgot that I need combustion air for the hot water heater. That being said, I'm sure that I can't simply remove the outside air tube.... I wonder if I'm best just leaving the whole system as is.

More time for this:
Old 12-10-07, 02:03 PM
Join Date: Nov 2007
Posts: 39
Yes, both the heater and hot water heater need intake air for combustion. The amount of heat they need is based on the amount of combustion they produce. I am not familiar with a formula but a Google search might help you find one.

Try "combustion make up air formula" and variations.

From the situation you describe, the best solution to piping in air for both appliances would be to locate them against a wall with proper spacing all around, then enclose them in a steel stud and drywall (5/8" green board both sides) closet so that the air can be piped in directly. Insulate it for added quiet. Make sure exhaust pipe size rules are observed if you have to move anything.

Add an operating door for access, or a removable stud panel, but be sure to leave some space for additional ventilation.

This should make your freezing basement less so. Good luck!
Old 12-10-07, 08:40 PM
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Join Date: Sep 2001
Location: Rochester, Minnesota
Posts: 18,427
Look into your install manual for the PVC sizing, and how to set it up once you get outside.

If you don't have the manual, let me know, I can get you a copy.

The make up is needed for your Dryer, Water Heater, Exhaust Fan. You can bring the pipe up another 4 to 5 feet up to act like a "Trap", that's what I did with mine.

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