MODEL F80A
DETERMING COMBUSTION AIR
DANGER
READ, UNDERSTAND AND FOLLOW ALL INSTRUCTIONS IN THIS SECTION. FAILURE TO PROPERLY VENT OR SUPPLY COMBUSTION AIR TO THIS FURNACE CAN CAUSE CARBON MONOXIDE POISONING, OR AN EXPLOSION OR FIRE, RESULTING IN PROPERTY DAMAGE, PERSONAL INJURY OR LOSS OF LIFE.
DANGER
THIS FURNACE AND ANY OTHER FUEL BURNING APPLIANCE MUST BE PROVIDED WITH ENOUGH FRESH AIR FOR PROPER COMBUSTION AND VENTILATION OF THE FLUE GASES. MOST HOMES WILL REQUIRE THAT OUTSIDE AIR BE BROUGHT TO THE FURNACE AREA. FAILURE TO DO SO CAN CAUSE PERSONAL INJURY OR DEATH FROM CARBON MONOXIDE POISONING.
CASE 1:
FURNACE LOCATED IN AN UNCONFINED SPACE
Unconfined space does not necessarily mean that combustion and ventilation will not have to be introduced from the outdoors, particularly in airtight homes. Refer to the appropriate installation code requirements regarding the minimum combustion air required for all fuel burning appliances located within the unconfined area.
If the amount of combustion and ventilation air is insufficient to properly operate the furnace and other fuel burning appliances within the unconfined area, it will be necessary to supply it from the outdoors based on the criteria used when calculating the air supply for a confined space.
NOTE: If planning to use the inside air of an unconfined space, remember to test for proper furnace operation (as well as other fuel burning appliances located within the unconfined space) with respect to adequate combustion and ventilation air with fireplace dampers open, clothes dryer running, bathroom exhaust fans on, kitchen range hood on, etc.
CASE 2:
FURNACE LOCATED IN A CONFINED SPACE
A confined space, (any space smaller than the minimums discussed in CASE 1), must have two air openings one within 12 inches of the ceiling and the other within 12 inches of the floor. The air openings must be sized based on whether the combustion and ventilation air is being taken from indoors or outdoors, the method outdoor air (if used) is introduced, and taking into account any other fuel burning appliances in the confined space.
If sufficient indoor combustion and ventilation air is available for the furnace and all other fuel burning appliances, even when clothes dryers, bathroom fans, range hoods, etc. are running, size each opening according to the appropriate installation codes.
NOTE: If using grilles to cover the two openings, factor in the free area of the grille. Typically, a grille will have a free area approximately 50% of its nominal size. Consequently, if the required opening is 10 inches x 10 inches , it will have to be doubled if using a sidewall grille with 50% free area.
IMPORTANT: If an exhaust fan, fireplace, clothes dryer or any similar device is present in the indoor area from which the combustion and ventilation air will be drawn, negative pressure could be a problem if natural infiltration from the outdoors does not match the rate at which air is exhausted.
CASE 3:
FURNACE LOCATED IN A CONFINED SPACE, OUTDOOR AIR FROM ATTIC OR CRAWL SPACE
In this circumstance, refer to the appropriate installation code for the free area of the combustion and ventilation air openings. If other fuel burning appliances are present, their combustion air and ventilation air requirements must be added to those of the furnace.
CASE 4:
FURNACE LOCATED IN A CONFINED SPACE, OUTDOOR AIR DUCTED HORIZONTALLY
Similar to CASE 3, outdoor air for combustion and ventilation may be drawn through horizontal ducting. Consult the appropriate installation code for the free area for openings. If other fuel burning appliances are present, their combustion air and ventilation air requirements must be added to those of the furnace.
IMPORTANT: The outdoor grilles must be installed in a location where they will not be obstructed in any manner.
IMPORTANT: If grilles are used on the outside wall, they must be sized properly. Most sidewall grilles have only 50% free area, so the grill size opening must be twice the size of the free air opening requirement.
WARNING
DO NOT ALLOW GAS PIPING TO BE ROUTED THROUGH JOIST SPACES THAT ARE USED FOR RETURN AIR PURPOSES. DO NOT USE JOIST SPACES FOR RETURN AIR PURPOSES IF THE JOIST SPACE ALREADY CONTAINS PLUMBING STACKS, CHIMNEY COMPONENTS, ETC. UNLESS THE PORTION USED FOR RETURN AIR PURPOSES CAN BE COMPLETELY ISOLATED FROM PORTIONS WITH OTHER USAGES.
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