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Calculating Combustion Air

 
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Old 03-08-2017, 09:03 PM   #1
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Calculating Combustion Air


Looking at two 50 gallon power vent water heaters. Not direct vent so I need combustion air. Total BTU is 80,000 so if I follow the code

2009 IRC - Combustion air requirement = 80,000/1000*50CF = 4000cf.

I got 1920 cf in the utility room and 7500cf in the basement adjacent. So My understanding is that I only need two 100 square inch louvers in the wall separating the utility room and the basement. One up high and one down low. That sound right? Apreciate your insight!
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Old 03-08-2017, 09:30 PM   #2
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Re: Calculating Combustion Air


You need 2- 12x12 louvers one installed 12" from the ceiling and second installed 12" from the floor and that should do it.

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Old 03-09-2017, 12:19 AM   #3
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Re: Calculating Combustion Air


Why not use outside air to save $, a insulated 3" or 4" pipe to the sunny side of the house above the snow line,saving the cost of burning A.C. in the summer, Heated air in the winter?

A back up flapper vent on the doorway to the Hot water heater closet...

Do you have to adjust the jet or air flow at your altitude?
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Old 03-09-2017, 05:23 AM   #4
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Re: Calculating Combustion Air


That would be 2-100 sq in free area louvers. So as posted earlier, 2-12x12s.
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Old 03-09-2017, 06:27 PM   #5
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Re: Calculating Combustion Air


You could build an insulated room around the HW heaters to isolate the waste heat by slowing the heat flow into the Air conditioned spaces during the A.C./dehumidifier seasons, closing any air returns or supplies from the A.C./furnace duct-work.

And of course reopening the ducts to spread out the "waste" heat in the heating season.

In modern super tight home, the suction of a radon gas blower, bath vent fans and appliances such as cloths dryers and Range hoods need to be considered regarding the creation of a negative draft that would cause exhaust gases to fill interior spaces....

Even a dry floor drain trap can allow the DVW roof stack to suck air out of confined basements. Or emit toxic sewer gases.
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