# Need help on comb air



## CC Plumbing (Feb 23, 2013)

Taking test tmrw need help


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## rjbphd (Feb 5, 2010)

CC Plumbing said:


> Taking test tmrw need help


So you want us to guess for you?


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## CC Plumbing (Feb 23, 2013)

rjbphd said:


> So you want us to guess for you?


Sure...ark Jman


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## CC Plumbing (Feb 23, 2013)

CC Plumbing said:


> Sure...ark Jman


Failed the portion on combustible air, I know there is a simple equation(s) I just don't remember them and the masters around here too busy apparently


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## rjbphd (Feb 5, 2010)

CC Plumbing said:


> Failed the portion on combustible air, I know there is a simple equation(s) I just don't remember them and the masters around here too busy apparently


 You have any boiler or furance manuels around?? There's a section about make up air for amount btu going in.. I think its 10 to1..


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## CC Plumbing (Feb 23, 2013)

rjbphd said:


> You have any boiler or furance manuels around?? There's a section about make up air for amount btu going in.. I think its 10 to1..


Sizing the combustible air ventilation for heaters/furnaces


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## rjbphd (Feb 5, 2010)

CC Plumbing said:


> Sizing the combustible air ventilation for heaters/furnaces


That's what I said.. every boiler or furance manual will have that information... go find one


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## Coolcanuck (Jan 30, 2012)

Tough question, there's a lot in the code book on sizing air, should do a webinar to help him in the rewrite lol


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## plbgbiz (Aug 27, 2010)

CC Plumbing said:


> Failed the portion on combustible air, I know there is a simple equation(s) I just don't remember them and the masters around here too busy apparently


Do you recall the questions that stumped you and was it combustion air for water heaters?


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## James420 (Nov 14, 2012)

plbgbiz said:


> Do you recall the questions that stumped you and was it combustion air for water heaters?


I believe some States are 50 cubic ft of air to 1000 btu's. 

Total BTU's divided by 1000 x 50.

I'm only posting this because tonight I was called out to a Bradford White, 48 gallon gas water heater, that the pilot went out on and the customer couldn't re light. Its a standard (atmosphere) vent water heater. Anyway this water heater also does some space heating, and is a 2nd home (rental). The water heater was installed in 2010, and they started having problems with it this year.

Its in a shed attached to the house, the shed is insulated and is only 8ft long x 4 ft wide x 7ft high. The water heater is 61,000 BTU. 

I'm coming up with 224 cubic feet, but the water heater I believe needs close to 3000 cubic feet. Are water heaters calculated differently? This seems to easy, what am I missing ?


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## CC Plumbing (Feb 23, 2013)

Just the sizing for the horizontal ducts, vertical. I took it Friday and see if I passed it. Rest of test blew through just that crap has been stumping me. Have to size flu also with fan assisted appliances


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## Plumbus (Aug 4, 2008)

http://www.nachi.org/forum/f20/combustion-air-requirements-gas-furnaces-26865/


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