adequate combustion air?


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Old 08-21-06, 11:05 AM
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adequate combustion air?

Today's project: evaluate adequacy of combustion air.

"normal" basement, not unusually tight. Adjoins a garage. Dimensions 24x24x7 for a volume of 4032 cubic ft.

Two appliances in this room: one gas-fired boiler, Burnham 206 (164mbh input, 118mbh IBR output). Boiler has a power venter with a draft proving switch. One electric dryer.

My understanding is that this boiler requires about 40 cfm.

I also understand that one way to evaluate whether the room can supply adequate combustion air is to take the room volume and divide by 50 to get the max appliance possible, in mbh.

If true, then the max appliance is 81 mbh and we FAIL to supply adequate air by half. If so, ouch.

Am I doing this right?

Thanks.
 
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Old 08-21-06, 11:30 AM
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Read pages six through eight.

http://www.hvac-direct.com/pdf_files/installation/504472b.pdf
 
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Old 08-21-06, 12:51 PM
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Thanks. Understood.

Here's how I did this:

Room volume = 4032 cf. The code(s) referenced in the PDF define confined space as <50 cf per 1000 BTU/hr input rating.

That limits the room to up to 81k BTU/hr input in order to not be treated as a confined space. At 164k input, we fall short by 83k BTU. Seems like a factor of two shortfall is significant.

So, it would appear that make-up air is a code requirement.

So, I called the local plumbing inspector. He said "don't worry about it, you're fine. As long as you're getting a decent flame, I've been doing this for 40 years, nothing unusual about your setup, etc."

What to think?
 
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Old 08-21-06, 01:31 PM
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All life is a compromise.

I tried to find a site that would explain it but...

Your calculations show that you are deficient but your inspector states that it is not a problem, who/what to believe?

This is why I like sealed-combustion burners, they draw all of their combustion air from outside. I know, doesn't help you in this instance.

Your combustion air is being drawn from the space that your boiler/burner is located (I know that you already know this) but where/how does this air enter into this space? Obviously through less-than-perfect sealing around the doors, windows, sills and other construction separating the space from the great outdoors.

If you are concerned (and I would be if it were my home) I suggest that you test the differential pressure between the utility room and outside. You will need a manometer (you can make one from some clear tubing) or if you want to spend about $50 to $75 I would suggest a Dwyer Magnahelic gauge calibrated 0 to 1 inch water column. You would connect the high-pressure side of the manometer to the outside air (you need to seal the hole the tube runs through) and have the low-pressure side open to the utility room. Try all combinations of boiler and dryer running with all of the exhaust fans and fireplaces in the living quarters. I would be concerned if the differential pressure ever exceeded 0.2 inches of water column with the utility room being negative compared to the outside.

Let me know if you need detailed information for a home-made manometer.
 
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Old 08-21-06, 02:01 PM
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Science project! Sure, lay it on me. Thanks.
 
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Old 08-21-06, 07:03 PM
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I had written this up for a competing forum but it seems to have been deleted. I will give the details on building a manometer but it might be a few days before it gets posted.
 
 

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