Residential Standard Gas Water Heater Service Handbook • 23
SUPPLEMENTS
Table 5.
Minimum Free Area of Permanent
Openings for Ven
Ɵ
la
Ɵ
on
and
Combus
Ɵ
on Air Supply – All Air from
Outdoors Only.
Based on the total BTU/HR input
ra
Ɵ
ng for all gas burning appliances
within a con
fi
ned space.
Opening Source
Minimum Free Area
Per Opening (sq. in.)
*Direct to outdoors
1 sq. in. per
4,000 BTU/HR
(see Figure 25)
Vertical ducts
1 sq. in. per
4,000 BTU/HR
(see Figure 26)
Horizontal ducts
1 sq. in. per
2,000 BTU/HR
(see Figure 27)
Single Opening
1 sq. in. per
3,000 BTU/HR
(see Figure 28)
*These openings connect directly
with the outdoors through a
ventilated attic, a ventilated crawl
space, or through an outside wall.
B5: Check that air source is clean
and free of chemicals
Air for combustion and ventilation
must be clean and free of corrosive or
flammable chemicals. A failure due to
corrosive chemicals in the air is not
covered by the warranty. Combustion air
must be free of acid-forming chemicals
such as sulfur, fluorine, and chlorine. Be
sure that air at the vent inlets is free of
such chemicals.
B6: Check that combustion
ventilation is adequate
To confirm that your installation has
enough combustion air, conduct the
vent draft test on page 11 when
installation is finished.
Combus
Ɵ
on Air Supply Op
Ɵ
ons
Direct to outdoors openings
Figure 25.
Vertical duct openings
Figure 26.
Horizontal duct openings
Figure 27.
Single opening
Figure 28.
ATTIC INSTALLATIONS
1
WARNING!
• In all cases, a water heater must be
installed according to its installation
manual.
• Consult the local codes of your
area for specific ventilation and
combustion air requirements. In the
absence of local codes, follow the
National Fuel Gas Code (ANSI Z223.1-
current edition).
• Failure to follow these warnings
can lead to death, serious injury, or
property damage.
Overview
Attic installations are common in
some parts of the country. In most
cases, such installations are trouble
free. However, problems may arise
from poor ventilation, high ambient
temperatures, water leaks, and other
potential hazards. Such issues include
pilot outage, water damage to the
living spaces below, and elevated
water temperatures. Even so, these
problems can be addressed. Some of
the potential solutions are listed below.
Pilot Outage
Pilot outage is more common in attic
spaces and hot environments than
in other installations. The following
factors can contribute to pilot outage,
either individually or in combination:
• Elevated air temperature
• Insufficient makeup air (air needed
for the proper ventilation of
combustion gases)
• Blocked air screen or flame arrestor
• Improper venting of the water heater
• Decompression
• Wind
1
Originally published as “Issues
Related to Gas Water Heaters Installed in Attics
(Atmospheric Vent)”
(324841-000).
