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Example: Gas water heater 40000 BTU/Hr
Vent-free 18000 BTU/Hr
Total
= 58000 BTU/Hr
*Does not include direct-vent gas appliances. Direct-vent draws combustion air
from the outdoors and vents to the outdoors.
4. Compare the maximum BTU/Hr the space can support with the actual amount of BTU/Hr
used.
____________BTU/Hr (maximum the space can support)
____________BTU/Hr (actual amount of BTU/Hr used)
Example: 51200 BTU/Hr (maximum the space can support)
58000 BTU/Hr (actual amount of BTU/Hr used)
The space in the above example is unusually tight construction because the actual BTU/Hr
used is more than the maximum BTU/Hr the space can support. You must provide additional
fresh air. Your options are as follows:
A. Rework worksheet, adding the space of an adjoining room. If the extra space provides an
unconfined space, remove door to adjoining room or add ventilation grills between rooms. See
Ventilation Air For Combustion And Ventilation From Inside Building, page 23.
B. Vent room directly to the outdoors. See Ventilation Air For Combustion And Ventilation
From Outdoors, page 24.
C. Install a lower BTU/Hr heater, if lower BTU/Hr size makes room unconfined.
If the actual BTU/Hr used is less than the maximum BTU/Hr the space can support, the
space is an unconfined space. You will need no additional fresh air ventilation.
WARNING
YOU MUST PROVIDE ADDITIONAL
VENTILATION AIR IN UNUSUALLY TIGHT CONSTRUCTION.
