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combustion air


Wildwillie
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Help me here, I did an inspection today on a 21 year old house, the furnace and water heater are in a closet in the garage. The combustion air for both units comes from a big hole in the ceiling of the closet about 18" by 24". From my research I believe that this still needs an air tube to move air down for fresh combustion or a vent cut in one of the doors. Am I right, wrong. BTW I have learned so much watching the postings on these forums and I have learned how much I still need to learn

Thanks Guys

wildwillie

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Equipment in a confined space needs 2 vents - one w/in 12" of the top and one w/in 12" of the bottom of the space. Free area of each vent should be 1" for every 1000 Btu/h input of both appliances.

With the lower of the vents installed, any combustion then needs to be 18" above the adjacent garage floor.

Note: louvered covers over the openings reduces the free area: metal -25%, wood -75%.

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Originally posted by Wildwillie

Help me here, I did an inspection today on a 21 year old house, the furnace and water heater are in a closet in the garage. The combustion air for both units comes from a big hole in the ceiling of the closet about 18" by 24". From my research I believe that this still needs an air tube to move air down for fresh combustion or a vent cut in one of the doors.

Some AHJ's won't allow ahole in the door when it's in a garage

And, BTW, depending the AHJ, one way to bring air in from above without flooding the room with cold air is to use a gooseneck or containment box and an drop. (See attachment)

But some AHJ's might say that doesn't meet the opening at the top rule.

Since no one I've talked to has been able to explain the rule for 1/2 high 1/2 low, and since air seems to find its way through either, ....

Download Attachment: icon_photo.gif ExteriorAirSupply02.jpg

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That picture on the right looks like a Polish Damper, (Not to offend anyone)

Use to see that in boiler/mechanical rooms in the Chicago area.

A 6" vent 90, extends into a 5-gallon bucket. Believe it or not, but the cold air stays in the bucket.

Eastern European Ingenuity...

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Originally posted by fqp25

That picture on the right looks like a Polish Damper, (Not to offend anyone)

Eastern European Ingenuity...

Well, I don't speak Polish myself, so I'm not as bright as the average 3 year Pole ....

Ah well.

It works!

BTW, the drawings are from the Jim Davis's CO and Combustion Analysis coursebooks

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Originally posted by StevenT

I am involved in a situation where fresh air is needed in a basment, not for combustion, but for breathing purposes. Would the gooseneck/containment box theory work in this situation too?

What about if the wind is blowing outside?

I suspect not, or not well - not without something moving air out of the space (like rising flue gases)

Although, there is negativepressure typically in basements, so maybe, especially if it is an older, less tightly built house.

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