All air from outdoors, Louvers and grilles – Whirlpool Residential Gas Water Heater with the Flame Lock Safety System User Manual

Page 9

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9

All Air from Outdoors

Outdoor fresh air can be provided to a confined area either
directly or by the use of vertical and horizontal ducts. The
fresh air can be taken from the outdoors or from crawl or
attic spaces that freely communicate with the outdoors.
Attic or crawl spaces cannot be closed and must be
properly ventilated to the outside.
Ductwork must be of the same cross-sectional area as
the free area of the opening to which they connect. The
minimum dimension of rectangular air ducts cannot be less
than three inches.
The size of each of the two openings is determined by the
method in which the air is to be provided. Refer to Table
3 to calculate the minimum free area for each opening.
Figures 6, 7, and 8 are typical examples of each method.

Louvers and Grilles

In calculating free area for ventilation and combustion
air supply openings, consideration must be given to the
blocking effect of protection louvers, grilles, and screens.
These devices can reduce airflow, which in turn may
require larger openings to achieve the required minimum
free area. Screens must not be smaller than 1/4” mesh. If
the free area through a particular design of louver or grille
is known, it should be used in calculating the specified free
area of the opening. If the design and free area are not
known, it can be assumed that most wood louvers will allow
20 - 25% of free area while metal louvers and grilles will
allow 60 - 75% of free area.
Louvers and grilles must be locked open or interconnected
with the equipment so that they are opened automatically
during equipment operation.
Keep louvers and grilles clean and free of debris or other
obstructions.

Table 3

Minimum Free Area of Permanent Openings for Ventilation and

Combustion Air Supply - All Air from Outdoors Only.
Based on the total BTU/HR input rating for all utilizing equip-

ment within the confined space.

Opening Source

Minimum Free Area

Per Opening (sq. in.)

Reference

Drawing

* Direct to outdoors 1 sq. in, per 4000 BTU/HR

Figure 6

Vertical ducts

1 sq. in, per 4000 BTU/HR

Figure 7

Horizontal ducts

1 sq. in, per 2000 BTU/HR

Figure 8A

Single Opening

1 sq. in, per 3000 BTU/HR

Figure 8B

Example: A water heater with an input rate of 50,000 BTU/HR

using horizontal ducts would require each opening to have a

minimum free area of 25 square inches.
Minimum free area = 50,000 BTU/HR x 1 sq. in. / 2000 BTU/HR =

25 Sq. Inches.

*

These openings connect directly with the outdoors

through a ventilated attic, a ventilated crawl space, or
through an outside wall.

Consult the local codes of your area for specific ventilation
and combustion air requirements.

Confined

Space

Figure 8A

All Air from Outdoors

Using Horizontal Ducts

Outdoor

Air Ducts

Outlet

Inlet

1 sq. inch

per

2000 BTU/HR

1 sq. inch per

4000 BTU/HR

Confined

Space

Figure 6

All Air from Outdoors; Inlet Air from Ventilated

Crawl Space/Outlet Air to Ventilated Attic

Inlet air

from the

crawl

space

Install above

insulation

Gable vent

to outdoors

Outlet

air to attic

1 Sq. inch per

4000 BTU/HR

Alternate

Air Inlet

Open

Foundation

Vent

Confined

Space

Figure 7

All Air from Outdoors

Through Ventilated Attic

Inlet air duct

1 sq. inch per

4000 BTU/HR

Install above

insulation

Gable vent

to outdoors

Outlet air

to attic

1 Sq. inch per

4000 BTU/HR

12” maximum

1 sq. Inch

per

2000 BTU/HR

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