Ventilation and Combustion Air
An oil-fired furnace should be located where a sufficient supply of air is available for combustion, proper venting, and the maintenance of suitable ambient temperature. In buildings of exceptionally tight construction, an outside air supply should be introduced for ventilation and combustion purposes.
If the furnace is located in a confined space such as a furnace room, closet, or utility room, the enclosure should be provided with two permanent openings for the passage of the air supply. One open- ing should be located approximately 6 in from the top of the enclo- sure, and the other opening approximately 6 in from the bottom. Each opening should have free area of at least 1 in2 per 1000 Btu/h (minimum size 100 in2) of the total input rating, or 1 ft2 per gallon of oil per hour.
The size of the openings must correspond to the bonnet capacity of the furnace. Furnace manufacturers generally recommend
suitable sizes for air openings in their equipment specifications (Table 12-2).
Air from an attic or a crawl space can also serve as a ventilation and combustion air supply to a confined furnace. Suitable openings near (or on) the floor and near (or on) the ceiling must be provided for the passage of the air.
When an oil furnace is installed in an unconfined area, such as a full basement, the full amount of air necessary for combustion is generally supplied by infiltration. Only when the construction is exceptionally tight is it necessary to provide openings to the outdoors.