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 BTU/HR of the total input for all gas appliances. The table below shows a few examples of the minimum square footage (area) required for various BTU/HR inputs.
Table 3 |
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BTU/HR | Minimum Square | Typical Room | |
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Input | with 8' Ceiling | ||
8' Ceiling | |||
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30,000 | 188 | 9 x 21 | |
45,000 | 281 | 14 x 20 | |
60,000 | 375 | 15 x 25 | |
75,000 | 469 | 15 x 31 | |
90,000 | 563 | 20 x 28 | |
105,000 | 657 | 20 x 33 | |
120,000 | 750 | 25 x 30 | |
135,000 | 844 | 28 x 30 | |
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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
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 6.
The size of each opening (free area) is determined by the total BTU/HR input of all gas utilization equipment (i.e., water heaters, furnaces, clothes dryers, etc.) and the method by which the air is provided. The BTU/HR input can be found on the water heater data plate. Additional air can be provided by two methods:
1.All air from inside the building.
2.All air from outdoors.
Figure 6 | 12” maximum |
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rooms within the building
12” maximum 
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 BTU/HR of the total input rating of all gas utilization equipment in the confined area, but not less than 100 square inches (Figure 7).
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