COMBUSTION AIR CALCULATIONS FOR A WATER HEATER CLOSET

[Lizramlu]

Hello everybody, I would like to know how to do the calculations for a water heater closet that is located on a interior space. I have a proposed 2' 10'' x 2' 8'' water heater closet and the water heater is a 38,000 btuh and the type is natural gas. I would leave a picture with more details. Hope someone can help me with this
Thanks in advance.

 

[Mr. Inspector]

manufactures installation instructions.

 

[Gregg Harris]

Hello everybody, I would like to know how to do the calculations for a water heater closet that is located on a interior space. I have a proposed 2' 10'' x 2' 8'' water heater closet and the water heater is a 38,000 btuh and the type is natural gas. I would leave a picture with more details. Hope someone can help me with this
Thanks in advance

 

[Gregg Harris]

702.3.2 Size ofopenings. The net free area ofeach opening,calculated in accordance with Section 708, shall be a minimum of 1 square inch per 1,000 Btu/h (2201 mm2/kW) ofinput rating of the fuel-burning appliances drawing combustion and dilution air from the communicating spaces andshall be not less than 100 square inches (64516 mm2).

 

[Mr. Inspector]

702.3.2 Size ofopenings. The net free area ofeach opening,calculated in accordance with Section 708, shall be a minimum of 1 square inch per 1,000 Btu/h (2201 mm2/kW) ofinput rating of the fuel-burning appliances drawing combustion and dilution air from the communicating spaces andshall be not less than 100 square inches (64516 mm2).

My 2018 IMC does not have anything for sizing combustion air for natural gas or any other fuel. Which code was this?

 

[mtlogcabin]

2018 IMC
SECTION 701
GENERAL

701.1 Scope.
Solid fuel-burning appliances shall be provided with combustion air in accordance with the appliance manufacturer’s installation instructions. Oil-fired appliances shall be provided with combustion air in accordance with NFPA 31. The methods of providing combustion air in this chapter do not apply to fireplaces, fireplace stoves and direct-vent appliances. The requirements for combustion and dilution air for gas-fired appliances shall be in accordance with the International Fuel Gas Code.

 

[SCBO1]

Does a louvered door or a Hi-Low wall vent solve the issue? Outside air brought into the closet?

I'd make sure the door opening is large enough for the appliance, some 50-gal WH's are almost 24" in diameter.

I'll give it a shot:
38,000btu x 50 = 1,900,000 ÷1,000 = 1,900cf
2'10" x 2'8" x "a"
(34" x 32" x 96") = 104,448 ÷144 = 725.3 cf

Does not appear to be enough combustion air?
("a" Assumed 8ft ceiling)

Are my calcs correct?

 

[klarenbeek]

2021 IFGC (this section hasn't changed significantly for years)
Taking combustion air from indoors:
304.5.3.1 Combining spaces on the same story (summarized version). 2 openings into an adjoining space that's not a bathroom or sleeping room. One within 12" of the ceiling and one within 12" of the floor, minimum 100 square inches of free area.
I've always accepted a full louvered door as two permanent openings. Not louvered on only top or bottom half.
Ballpark guideline, a 14x16x8 room is enough cubic feet for about 40,000 BTUs.

Taking combustion air from outdoors (both summarized):
304.6.1 Two-permanent opening method. One opening within 12" of the ceiling and one within 12" of the floor. Each opening shall have 1 square inch per 4000 BTU if communicating directly to the outdoors, or 1 square inch per 2000 BTU if communicating to the outdoors through ducts.
304.6.2 One-permanent opening method. One opening within 12" of the ceiling. Opening size is 1 square inch per 3000 BTUs. Appliance needs minimum 1" clearance to the back and sides and 6" clearance in front.

 

[klarenbeek]

(34" x 32" x 96") = 104,448 ÷144 = 725.3 cf

34x32x96= 104,448/1728= 60.44 cf

144 square inches in a square foot. Take that times 12 to get 1728 cubic inches in a cubic foot.

 

[SCBO1]

34x32x96= 104,448/1728= 60.44 cf

144 square inches in a square foot. Take that times 12 to get 1728 cubic inches in a cubic foot.

Thank you for checking my calcs!
I needed to use the correct multiplier for cubic inches.