Residential Standard Gas Water Heater Service Handbook • 21
SUPPLEMENTS
EVALUATING
COMBUSTION AND
VENTILATION AIR
SUPPLY
WARNING! Gas water heaters
require an adequate source of clean air
for combustion and ventilation.
Without sufficient air, a water heater
will have frequent pilot outages and
may emit excessive and abnormal
amounts of carbon monoxide.
Before beginning:
Calculate total BTU/HR rating of all
appliances
To calculate the combus
Ɵ
on air and
ven
Ɵ
la
Ɵ
on required, add up the total
BTU/HR ra
Ɵ
ngs of all gas burning
appliances (e.g., water heaters, furnaces,
clothes dryers) in the same area.
A water heater’s BTU/HR rating is on its
data plate, located next to the gas control
valve/thermostat. The BTU/HR ratings
should be on the other appliances’ data
plates. If you have trouble determining
the BTU/HR ratings, contact the
manufacturer.
NOTICE:
If you are
replacing an old water heater with one
that has a higher BTU/HR rating, the
amount of ventilation required may be
greater.
Example:
Gas Burning Appliance
BTU/HR Rating
Gas Water Heater
40,000
Furnace
75,000
Dryer
20,000
Total
135,000
Household Appliances:
Gas Burning Appliance
BTU/HR Rating
Gas Water Heater
Total
Table 2 provides examples of minimum
square footage (area) required for
various BTU/HR totals. Areas used for
storage or which contain large objects
containing less air than is assumed for
the room sizes in Table 4. See Option A
for more specific calculations.
Table 4.
BTU/HR
Minimum
Square
Feet with
8’ Ceiling
Typical
Room with
8’ Ceiling
30,000
188
9 x 21
45,000
281
14 x 20
60,000
375
15 x 25
75,000
469
15 x 31
90,000
563
20 x 28
105,000
657
20 x 33
120,000
750
25 x 30
135,000
844
28 x 30
Option A: Installation without
outside ventilation (not
recommended)
Ventilation with outside air is
recommended for all installations. Even
if the water heater is installed in a large,
open room inside the house, outdoor
air is usually needed because modern
homes are very tightly sealed and
often do not supply enough air to the
water heater. However, when installed
in a large indoor space, it may be
possible to provide enough air without
outside ventilation. If you are unsure
if the installation location has enough
ventilation, contact your local gas utility
company or code officials for a safety
inspection.
The following instructions will help
determine if it may be possible to install
without outside ventilation. Even if
this may be possible, you will need to
conduct the vent draft test on page 11
when installation is finished. If there is
not enough ventilation, you will need to
ventilate with outside air.
Check for Chemicals:
Installations where corrosive chemicals
may be present require outside air.
Air for combustion and ventilation
must be clean and free of corrosive or
acid-forming chemicals such as sulfur,
fluorine, and chlorine. Ventilation with
outside air will reduce these chemicals,
but it may not completely eliminate
them. Failure due to corrosive chemicals
is not covered by the warranty. Examples
of locations that require outside air due
to chemicals include:
• Beauty
salons
•
Photo processing labs
•
Indoor
pools
•
Laundry, hobby, or craft rooms
•
Chemical storage areas
Products such as aerosol sprays,
detergents, bleaches, cleaning solvents,
gasoline, air fresheners, paint and
varnish removers, and refrigerants
should not be stored or used near the
water heater.
A1: Calculate the air volume of
the room
Air requirements depend on the size of
the room.
Floor Area (Square feet) X Ceiling Height
(feet) = Room Volume (cubic feet)
If there are large objects in the room
(e.g., refrigerator, furnace, car), subtract
their volume from the volume of the
SUPPLEMENTS
