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Unconfined Space
A water heater in an unconfined space uses indoor
air for combustion and requires at least 50 cubic feet
for each 1,000 BTUH of the total input for all gas
appliances. The table below shows a few examples of
the minimum square footage (area) required for
various BTUH inputs.
Important:
!
The area must be open and be able to provide the
proper air requirements to the water heater. Areas
that are being used for storage or contain large
objects may not be suitable for water heater
installation.
!
Water heaters installed in open spaces in buildings
with unusually tight construction may still require
outdoor air to function properly. In this situation,
outside air openings should be sized the same as
for a confined space.
!
Modern home construction usually requires
supplying outside air into the water heater area.
Confined Space
1. All air from inside the building.
2. All air from outdoors.
For the correct and proper operation of this water
heater, ample air must be supplied for the combustion,
ventilation, and dilution of flue gases. Small enclosures
and confined areas must have two permanent openings
so that sufficient fresh air can be drawn from outside of
the enclosure. One opening shall be within 12 inches of
the top and one within 12 inches of the bottom of the
enclosure as shown in Figure 4.
The size of each opening (free area) is determined by
the total BTUH input of all gas utilization equipment
(i.e., water heaters, furnaces, clothes dryers, etc.) and
the method by which the air is provided. The BTUH
input can be found on the water heater data plate.
Additional air can be provided by two methods:
Figure 4
Opening Locations-
Confined Spaces
12” maximum
Permanent
openings to
the outside or
additional
rooms within
the building
Closet
or
other
confined
space
All Air from Inside the Building
When additional air is to be provided to the confined
area from additional room(s) within the building, the
total volume of the room(s) must be of sufficient size to
properly provide the necessary amount of fresh air to
the water heater and other gas utilization equipment in
the area. If you are unsure that the structure meets this
requirement, contact your local gas utility company or
other qualified agency for a safety inspection.
Each of the two openings shall have a minimum free
area of 1 square inch per 1,000 BTUH of the total input
rating of all gas utilization equipment in the confined
area, but not less than 100 square inches (Figure 5).
Confined
Space
Figure 5
All Air from Inside Building
Confined Space Installation
Permanent
Openings
1 square
inch/1000
BTUH
(min. 100
sq. In.)
30,000
45,000
60,000
75,000
90,000
105,000
120,000
135,000
188
281
375
469
563
657
750
844
9 x 21
14 x 20
15 x 25
15 x 31
20 x 28
20 x 33
25 x 30
28 x 30
Typical Room
with 8' Ceiling
Min. Sq. Feet with
8' Ceiling
BTUH
Input
Table 3
12” maximum
8