American Water Heater 317994-002 Manual De Usuario

12

12” Max.

Permanent
openings to 
the outside or
additional 
rooms within 
the building

Closet

or other

confined

space

12” Max.

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).

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 

4 to calculate the minimum free area for each opening. 

Figures 6, 7, 8A and 8B are typical examples of each 

method. 

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 4
Minimum Free Area of Permanent Openings for 

Ventilation and Combustion Air Supply - All Air from 

Outdoors Only.
Based on total BTUH input rating for all utilizing 

equipment within the confi ned space.

*Direct to outdoors

1 sq. in, per 4000 BTUH

Figure 6

Vertical Ducts

1 sq. in, per 4000 BTUH

Figure 7

Horizontal Ducts

1 sq. in, per 2000 BTUH

Figure 8A

Single Opening

1 sq. in, per 3000 BTUH

Figure 8B

Example: A water heater with an input rating of 50,000 BTUH using 
horizontal ducts would require each opening to have a minimum free 
area of 25 square inches.

Minimum free area = 50,000 BTUH x 1 sq. in. / 2000 BTUH = 25 sq. in.

*

  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

Permanent
Openings

1 Square 
inch/1000
BTUH
(min. 100
sq. in.)