Installation Guide

Residen al Standard Gas Water Heater Use and Care Guide • 9
GETTING STARTED
Residen al Standard Gas Water Heater Use and Care Guide • 9
GETTING STARTED
A2: Calculate required air volume
A water heater installed in an unconfi ned
a c or garage requires that the space
be at least 50 cubic feet per 1,000 BTU/
HR of the total input for all gas burning
appliances in the same area.
[Total BTU/HR/1000] x 50 = Cubic feet
of air required.
Example:
(135,000 / 1000) x 50 = 6,750
If the air volume of the room is less
than the required air volume, you must
provide two permanent outside air
openings that draw in suffi cient air. Use
Op on B.
If the air volume of the room is greater
than the required air volume, it may
be possible to install the water heater
without outside ven la on.
A3: Check that combus on ven-
 la on is adequate
Because modern homes are o en well-
sealed to prevent dra s, even a large
room may not provide enough combus-
 on air without ven la on. To con-
fi rm that your installa on has enough
combus on air, conduct the vent dra
test on pages 23-24 when installa on is
fi nished.
Op on B: Install with outside
ven la on
Ven la on with outside air is recom-
mended, and, for most installa ons, is
needed. There may be exis ng ven la-
 on that is adequate, or you may need
to add more ven la on.
Supplying outside air to typically requires
two openings. One opening must be
within 12 inches from the fl oor and
the second opening must be within 12
inches from the ceiling. Although a single
opening is not preferred, you may use a
single opening to outside air if the mini-
mum free area is sized according to Table
3. Two openings must be used when
ven la ng with air from another room.
The outside air can be taken from a
crawl space or a c open to the out-
doors and adequately ven lated. You
may use ver cal or horizontal ducts.
B2: Determine type of ven la-
 on
There are several types of ven la on
that can be used :
1. Direct to outdoors
2. Ver cal ducts
3. Horizontal ducts
4. Single opening (not recom-
mended; must be at least 100
square inches. Not appropriate
for confi ned spaces smaller than
50 cubic feet per 1,000 BTU/HR as
calculated in sec on A or when
ge ng air from another room.)
5. From a larger room inside the
house (not recommended – refer
to sec on A above to determine if
the combined volume of the rooms
may be adequate).
B3: Determine minimum free
area required for each vent
opening
The size of the vent openings depends
on the total BTU/HR ra ng of all appli-
ances in the space (use your calcula on
from “Before beginning”) and the type
of vent used. Table 3 provides the mini-
mum free area for each vent opening
depending on the type of ven la on.
B4: Calculate minimum size of
vent openings and ducts
The vent cross-sec onal area needed to
provide the free area depends on the
covering on the vent openings. Typical
vents use louvers or grilles to protect
the opening. The louver or grill itself
blocks some of the free area, so the
opening may need to be larger to meet
the minimum free area requirements.
Use the following formula to calculate
the required cross-sec onal area:
Cross-sec onal area = minimum free
area required ÷ percent free area of
Table 3
Minimum Free Area of Permanent Openings for Ven la on and Combus on Air
Supply – All Air from Outdoors Only.
Based on the total BTU/HR input ra ng for all gas burning appliances within a
confi ned space.
Opening Source Minimum Free Area
Per Opening (sq. in.)
*Direct to outdoors 1 sq. in. per 4,000 BTU/HR (see fi gure on page 10)
Ver cal ducts 1 sq. in. per 4,000 BTU/HR (see fi gure on page 10)
Horizontal ducts 1 sq. in. per 2,000 BTU/HR (see fi gure on page 10)
Single Opening 1 sq. in. per 3,000 BTU/HR (see fi gure on page 10)
*These openings connect directly with the outdoors through a ven lated a c, a
ven lated crawl space, or through an outside wall.