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kherr
Premium
join:2000-09-04
Collinsville, IL

90+ Furnace Combustion Air Intake

Should it be pitched towards the outside or furnace ??



nunya
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join:2000-12-23
O Fallon, MO
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That's a good question, and I don't know the proper answer.

I do know that in the winter, I often see both pipes with icicles on them at houses I'm visiting.
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Lurch77
Premium
join:2001-11-22
Oconto, WI
kudos:4
reply to kherr

It will be pitched back to the furnace. Check the installation manual. It will give exact details concerning venting, including amount of elbows, sizing, and length. Incorrect venting can void the warranty and cause running issues. Generally it is pitched toward the furnace at least 1/4 inch per foot. No sags, no traps. You need the condensate to flow freely back to the furnace.


kherr
Premium
join:2000-09-04
Collinsville, IL
Reviews:
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No such thing as paperwork although I probably could google a model number if I can figure out where it is. I've already looked on the outside that isn't covered up. I really didn't want to open it. It's close to 15' including the riser with a 90 and 2-45's.

I don't know why they didn't hook it up when they installed it. There was no one at the house when they were there. But then again I've let it slide for about 12 years are so.



pende_tim
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join:2004-01-04
Andover, NJ
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reply to Lurch77

I think the OP was asking about the fresh air intake line. There should be no combustion condensate in the intake line.

For lack of paper work on the unit, I would pitch it towards the furnace only if there was a 45 or 90 on the outside 3" pipe end that was well glued and acted as a rain hood. There also should be a T trap at the furnace to catch any stray moisture that may find it's way down the pipe.

I assume the reason this is recommended is so that any moisture that may get into the pipes will drain back towards a warm environment and stay liquid. If the pitch was to the outside, ice could build in very cold weather and impede airflow.

If this is a new air intake install be sure to check for any separation required between the combustion vent and the fresh air intake. Typically this is 2-3 feet. You do not want to draw any combustion air ( and CO ) back into the house.
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The difference between genius and stupidity is that genius has its limits.



Lurch77
Premium
join:2001-11-22
Oconto, WI
kudos:4

Crap. I realize now I missed that part, for some reason. But the rules remain the same. You need a certain amount of size for a given length and amount of elbows if it vented from elsewhere. And be sure the intake opening at the outdoors is near the exhaust, to ensure equalized air pressures. Some manufacturers allow running it without exterior intake venting. But in this case you need to have plenty of combustion air. If your furnace is in an large space and has been running well for the last 12 years, it may not be anything to worry about. Grab the model and look up the paperwork online to be sure what they want.


kherr
Premium
join:2000-09-04
Collinsville, IL
Reviews:
·Charter

I guess I'll take off the front panel and see if there's a plate with model #. The main reason I was wanting to finish it is so there's one less draft coming from basement door. The spot I'm eyeing is about 3' from the vent. It's pretty much the only spot I can weave through other pipes/ducts.



Msradell
P.E.
Premium
join:2008-12-25
Louisville, KY
reply to kherr

Where is the combustion air being pulled from? Many of these units allow it to be pulled from an unconditioned area (such as attic or garage) without being directly vented to the outside. It may be why it wasn't done at the time of installation.


kherr
Premium
join:2000-09-04
Collinsville, IL
Reviews:
·Charter

After a couple of hours I finally found where they had chart/dimensions/rules for my project. Rudd's site was totally useless. After refining the wording on the search, google finally coughed up something useful. I am well within the way I was going to do it.

Even though it was setup for inside air, your still pulling air from the outside, so I might as well do it so I don't have to heat it as well. It's setting next to a gas w/h. All the installs I've ever seen like that use outside air. Too many appliances competing for the same combustion air.



ArgMeMatey

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Milwaukee, WI
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said by kherr:

Even though it was setup for inside air, your still pulling air from the outside, so I might as well do it so I don't have to heat it as well. It's setting next to a gas w/h. All the installs I've ever seen like that use outside air. Too many appliances competing for the same combustion air.

I have my furnace right next to the water heater as well. The water heater was replaced first; it's a direct vent with coaxial exhaust/intake. When the furnace installers came, I was disappointed that they said they had to locate their pipes six feet horizontally from the water heater cap. So I have these 3" PVC pipes running across the basement ceiling for six feet instead of straight out a single joist space like I'd pictured.
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