House of Craig - WSSC Combustion Air Requirements Calculator
- There are 3 appliances in a 14'x10' furnace room in a house with 8' ceilings whose combined total input is 180,000, can all combustion air be taken from inside this room?
- Fill in the Square Feet of Indoor Area with 8' Ceiling box with 140 (14x10=140) and click the calculate button. The Input BTUH of appliance(s) box tells you that a maximum of 16,800 btuh's can be supported by the volume in the furnace room, this room is nowhere near enough by itself.
The furnace room is not large enough, now what?
- Fill in the Input BTUH of appliance(s) box with 180000 and click the calculate button. the Square Feet of Indoor Area with 8' Ceiling box tells you the total requirement for these appliances is 1500 square feet. If the area of adjacent room(s) totals 1360 square feet (1500 total requirement - 140 for the furnace room) or more, then installation of high and low pass-thru grilles connecting the furnace room to the adjacent area(s) will meet the requirements. The Square Inches of Free Area of One of the 2 Pass-Thru Grilles box tells you these grilles need to each be 18x10 or larger.
The adjacent area is only 800 square feet, now what?
- Fill in the Square Feet of Indoor Area with 8' Ceiling box with 800 and click the calculate button. The Square Inches of Free Area of One of the 2 Pass-Thru Grilles box tells you that now these grilles need only be 10x10 each.
Ok, what about the shortfall?
- Fill in the Square Feet of Indoor Area with 8' Ceiling box with 560 (the 1500 total square footage requirement - the furnace room(140) + the adjacent area(800) or 1500-940=560) the Square Inches of Free Area of Opening/Duct to the Outside box tells you that in addition to the adjacent area's volume you will need to cut or find openings totalling 33 square inches between the furnace room and the outside to meet the rest of the requirement.
WSSC Requirements Used by this Calculator
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- For all air from inside the structure: The room shall have not less than 1 cubic foot of volume per 15 btuh total equipment load.
- For pass-through openings between adjacent spaces: The total net free area of the openings shall be equal to 1 square inch per 500 btuh of the equipment rating.
- For air from outside: When connected to the outdoors thru horizontal ducts, the opening area shall equal 1 square inch net free area per 2000 btuh total input rating of equipment