Installing Your Furnace
8
Combustion & Ventilation Air (continued)
LOUVERS / GRILLES AND SCREENS COVERING
FREE AREA OPENINGS
If a screen is used to cover the opening(s), it must not be smaller
than 1/4-inch mesh. Use the free area of a louver or grille to
determine the size opening required to provide the free area
specified. If the free area is not known, assume a 20% free area
for wood and a 60% free area for metal louvers or grilles.
INFILTRATION AIR
If your furnace is in an open area (unconfined space), the air that
leaks through the cracks around doors and windows may be
enough for combustion and ventilation air. The doors should not
fit tightly. The cracks around windows should not be caulked or
weather stripped.
Spillage means air starvation. A fresh air duct or air intake
opening must be installed to provide air directly to the furnace or
other gas appliances.
If spillage exists or when the furnace is in a building of tight
construction where the windows and doors are weather stripped,
air for combustion and ventilation must be obtained from outdoors
or space open to the outdoors.
To determine if infiltration air is adequate, perform the following
checks:
1.
Close all doors and windows. If you have a fireplace, start a
fire and wait until flames are burning vigorously.
2.
Turn on all exhausting devices, i.e., kitchen and bathroom
exhaust fans; water heaters (gas and electric).
3.
Turn on all vented gas appliances, i.e., heating equipment
(includes any room heaters), water heaters.
4.
Wait ten (10) minutes for drafts to settle.
5.
Check for draft hood spillage at each appliance. Hold a lit
match two-inches from the draft opening. (Figure 2).
A. No Spillage
If the match flame pulls toward draft hood, this indicates sufficient
infiltration air. Return exhausting devices and appliances to the
condition you found them.
B. Draft Hood Spills
If there is spillage at a draft hood (match goes out or flame wavers
away from draft hood), check for plugged flue connectors and
chimneys. Repair blockage and test again.
If you have a fireplace, open a window or door near the fireplace
and then check for spillage. If spillage stops, do not use the
fireplace without a nearby window or door open until you can
supply fresh air by a permanent duct.
If you have kitchen and bathroom exhaust fans, turn them off and
check for spillage. If spillage stops, do not use exhaust fans
(circuit breakers for fans should be turned off) until you can supply
fresh air by a permanent duct.
Provide opening(s) having a total free area of one-square-inch per
4,000 Btu/hr. of the total combined input ratings for all appliances
in the area. The required free area is shown in Figure 3. This
fresh air opening or duct must terminate at a point not more than
one-foot above the floor. It must have at least one-square inch of
free area for each 4,000 Btu/hr. of input of all appliances in area.
Hole Placement - Example
Square inches
of Opening
