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Installation
The instructions below will help determine if the
water heater can be installed without outdoor
ventilation.
Calculate the total BUT/h rating of all equipment.
To calculate the required combustion air and
ventilation, add the BTU/h rating of all gas
appliances (e.g. water heaters, furnaces, dryers) in
the same area. Do not include appliances that are
directly ventilated. See the example below.
The BTU/h rating of your water heater is on the
nameplate. The BTU/h rating should be on the
rating plate of the other gas appliance. If you are
unsure of the BTU/h rating, contact the
manufacturer or have qualified personnel to
determine the ventilation requirements.
NOTICE
If you are replacing an old water heater
with a BTU/h rated higher water heater, the
amount of ventilation required may be
greater.
Example:
Gas appliance
Gas water heater
Stove
Dryer
Your appliance:
Gas appliance
Gas water heater
Calculating the amount of air in a room The air
demand depends on the size of the room.
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Room volume (ft ) = floor area (ft ) x ceiling height
(ft)
If there are large objects in the room (such as
refrigerators, stoves, cars), subtract their volume.
You can better estimate the available air.
Air volume = room capacity - object capacity
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BTU/h rated
120,000
75,000
20,000
Total
215,000
BTU/h rated
120,000
Total
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Note: Adjacent rooms with permanently open
doorways can be counted as part of the
calculation. Calculate the amount of air required to
install in an unrestricted attic, with a water heater
in the garage or space requiring a space of at least
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50 ft (1.42m ) total input of all gas appliances in
the same area per 10,000 BTU/h the amount.
Required air volume (ft ) = total energy level of the
equipment (Btu /h) x 50 ft /1000 (Btu/h)
Example: (294,000/1000) x 50 = 14,700 ft
If the air volume in the room is less than the
required air volume, the water heater must be
ventilated or lifted directly.
Provide a permanent external air opening to draw
in enough air. If you want to provide combustion
air for outdoor ventilation, go to "Using Outdoor
Ventilation Installation". If the amount of air in the
room is greater than the amount of air required,
the water heater can be installed without external
ventilation. However, the impact of the exhaust fan
must be considered. Exhaust fans can affect the
amount of combustion air available in your home.
Electric appliances such as stoves, whole house
fans and dryers will let the air out of the house. If
the air they pump out is faster than it can be
replaced, your water heater may not have enough
oxygen to properly ignite. It may also result in back
drafting, ie when negative air pressure is drawn
back through the chimney or appliance vents.
These events can cause unsatisfactory water heater
performance. The best solution is to direct the
water heater directly to vent or install a sufficient
number of supplementary vents.
Installation for outdoor ventilation is recommended
for outdoor air ventilation and is required for most
installations. There may be adequate ventilation or
you may need to increase ventilation. Supplying
outside air to a water heater typically requires two
openings. One opening must be 12 inches (305
mm) from the floor and the second opening must
be 12 inches (305 mm) from the ceiling. Although a
single opening is not preferred, if a minimum free
area is determined according to Table.
A single opening can be used to enter the outside
air. When using air from another room for
ventilation, two openings must be used. The
outside air can be taken out of the crawling space
or attic, leading to the outside and fully ventilated.
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