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Your water heater's BTU/h rating is on the rating plate. The BTU/h ratings should be on the other appliances'
rating plates. If you have trouble determining the BTU/h ratings, contact the manufacturer or have a qualified
person determine the ventilation requirements.
: If you are replacing your old water heater with one that has a higher BTU/h rating, the amount of
NOTICE
ventilation required may be greater.
Example:
Gas Burning Appliance
Gas Water Heater
Calculate the air volume of the room
Air requirements depend on the size of the room.
Room Volume (ft
) = Floor Area (ft
3
If there are large objects in the room (e.g., refrigerator, furnace, car), subtract their volume from the volume of the
room to get a better estimate of the air available.
Air Volume = Room Volume - Object Volume
NOTE: Adjoining rooms with permanently opened doorways can be counted as part of the calculation.
Calculate required air volume
A water heater installed in an unconfined attic, garage, or space requires that the space be at least 50 ft
m
) per 1,000 BTU/h of the total input for all gas burning appliances in the same area.
3
Required Air Volume (ft
Example:
(294,000 / 1000) x 50 = 14,700 ft
If the air volume of the room is less than the required air volume, you must direct vent the water heater or
provide permanent outside air openings that draw in sufficient air. Go to "Install with outside ventilation" if you
want to provide combustion air with outside ventilation.
If the air volume of the room is greater than the required air volume, it may be possible to install the water heat-
er without outside ventilation. However, be sure to consider the effects of exhaust fans.
Exhaust fans can affect the amount of combustion air that is available in your home. Appliances such as furnac-
es, whole house fans, and clothes dryers draw air out of your home. If they draw air out faster than it can be
replaced, your water heater may not have enough oxygen to fire properly. Back-drafting may also result, which is
when negative air pressure pulls air backwards through chimneys or appliance vents. These events can cause un-
satisfactory water heater performance. The best solution is to direct vent the water heater or install an adequate
number of make-up air vents. (See "Install with outside ventilation".) For more information, consult a qualified
technician or your local gas utility.
Install with outside ventilation
Ventilation with outside air is recommended, and, for most installations, is needed. There may be existing ventilation
that is adequate, or you may need to add more ventilation.
Supplying outside air to the water heater typically requires two openings. One opening must be within 12 in (305 mm)
from the floor and the second opening must be within 12 in (305 mm) from the ceiling. Although a single opening is
not preferred, you may use a single opening to outside air if the minimum free area is sized according to Table 1. Two
openings must be used when ventilating with air from another room.
The outside air can be taken from a crawl space or attic open to the outdoors and adequately ventilated. You may
use vertical or horizontal ducts.
BTU/h Rating
199,000
Furnace
75,000
Dryer
20,000
Total
294,000
) X Ceiling Height (ft)
2
) =Total Appliance Energy Rating (btu/h) X 50 ft
3
3
18
Your
Gas Burning Appliance
appliances:
Gas Water Heater
/ 1000 (btu/h)
3
Page
Installation Manual
Installation
BTU/h Rating
Total
(1.42
3
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