Loading ...
Loading ...
Loading ...
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.
Loading ...
Loading ...
Loading ...