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Old 10-16-2009, 03:28 PM   #1
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Want to install combustion air venting


I have a natural gas furnace that is power vented and uses the basement air for combustion, its a 1993 Heil furnace. Sticker inside says input BTU is 75,000 and output is 59,000. I want to install a duct that is located about 1 foot off the floor near the furnace to help supply combustion air to the furnace. I am thinking of installing 4 inch duct that is vented from the outside and has a motorized damper that opens when the furnace runs.

Is 4 inch sufficent?
Is a motorized damper needed or is there a passive type that would work?
Should the ducting be rigid and insulated?
Should a fan be installed to increase air movement toward the furance end?

Thanks for any input

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Old 10-16-2009, 04:45 PM   #2
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Want to install combustion air venting


Where is the furnace located?

If it is in a separate utility room with tight door, then a passive system will work. I have an intake from the roof the dumps into an open 5 gallon bucket to prevent siphoning.

If it is it is just standing in an open area, an active system will work, but it get complicated and more costly.

Dick

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Old 10-16-2009, 04:54 PM   #3
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Want to install combustion air venting


It is located in the middle of my basement, wide open space. By active are you talking about a motorized damper then? I read about using a bucket or box to prevent cold air "spilling" onto the floor, how does this work? Is a box or bucket simply placed under the end of the duct on the floor?
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Old 10-16-2009, 05:26 PM   #4
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Want to install combustion air venting


Thr "bucket method only works in a confined space. My townhouse (built in 1981) has this.

If it is in an open basement space, like yours, the furnace will draw combustion air from any area.

If you have very tight home, using a little of the interior air is not all that bad because it induces some fresh air exchange (if you do not have an air-to-air heat exchanger).

I chose an 80% furnace for my townhouse (1500 sf, only 2 sides exposed) because of the low heating demands even at -30F and the amount of thermal mass from the masonry and the problems of a 90%+ system venting. - Haven't been over $100/month (heat, water & drier) even in the worst of a Minnesota winter with a north and east exposure.

Dick
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Old 10-16-2009, 05:54 PM   #5
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Want to install combustion air venting


Every 16 year old Heil should have its heat exchanger checked for cracks and popped compression rings. VERY common problem with them. A Heil tech would know where to look for that. Not a DIY project.
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Old 10-16-2009, 06:58 PM   #6
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Want to install combustion air venting


Quote:
Originally Posted by yuri View Post
Every 16 year old Heil should have its heat exchanger checked for cracks and popped compression rings. VERY common problem with them. A Heil tech would know where to look for that. Not a DIY project.
We are changing out these furnaces regularly.
An alternative to the 'bucket' is to install the combustion air intake with a trap.
In other words, run the duct down the wall near floor, then a 'U' turn back up the wall a foot or two.
No snow yet Yuri; did you run out?
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Old 10-16-2009, 07:21 PM   #7
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Want to install combustion air venting


Back to "normal" now. It all melted in a hurry. Lots of no heat calls and $$ sales. Great Canadian tradition. Play the Grey Cup in a Blizzard. LOL. Wonder why they don`t start the season after the May long weekend. Our Bombers woke up from their coma and won 3 in a row.

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