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V Air for Combustion and Ventilation
Sufficient fresh air must be supplied for combustion and ventilation. Provisions for combustion and ventilation air for oil
burning equipment must be made in accordance with Section 1.5, Air for Combustion and Ventilation, in the latest edition
of Installation of Oil Burning Equipment (ANSI/NFPA 31).
To ensure an adequate supply of air for combustion, ventilation and flue gas dilution, start by determining whether the
boiler is to be installed in a building of unusually tight construction. A building of unusually tight construction is defined as
having all of the following features:
• Walls and ceilings exposed to outside atmosphere have a continuous water vapor retarder with a rating of 1 perm
or less with openings gasketed and sealed
• Weather stripping has been added on openable windows and doors
• Caulking and sealants are applied to areas such as joints around window and door frames, between sole plates and
floors, between wall-ceiling joints, between wall panels, at penetrations for plumbing, electrical, and gas lines, and
at other openings.
For Buildings of Other than Unusually Tight Construction
1) Determine whether the boiler is to be installed in a confined space - A confined space is defined as having a volume
less than 50 cubic feet per 1000 BTU/hr input of all appliances installed in that space. To determine whether the boiler
room is a confined space:
a. Total the input of all appliances in the boiler room in thousands of BTU/hr. Round the result to the next highest
1000 BTU/hr.
b. Find the volume of the room in cubic feet. The volume of the room in cubic feet is:
Length (ft) x width (ft) x ceiling height (ft)
In calculating the volume of the boiler room, consider the volume of adjoining spaces only if no doors are
installed between them. If doors are installed between the boiler room and an adjoining space, do not consider the
volume of the adjoining space, even if the door is normally left open.
c. Divide the volume of the boiler room by the input in thousands of BTU/hr. If the result is less than 50, the boiler
room is a confined space.
Example:
A TWZ090 and a water heater are to be installed in a room measuring 6 ft - 3 in x 7 ft with an 8 ft ceiling. The
water heater has an input of 30000 BTU/hr:
Input of TWZ090 = 0.90 Gal/hr x 140000 BTU/Gal = 126000 BTU/hr
Total input in thousands of BTU/hr = (126000 BTU/hr + 30000 BTU/hr)/1000 = 156
Volume of room = 6.25 ft x 7 ft x 8 ft = 350 ft
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350/156 = 2.24. Since 2.24 is less than 50, the boiler room is a confined space.
2) Unconfined Space - Natural infiltration into the boiler room will normally provide adequate air for combustion and
ventilation without additional louvers or openings into boiler room.
3) Confined Space - Provide two openings into the boiler room, one near the floor and one near the ceiling. The top edge
of the upper opening must be within 12” of the ceiling and the bottom edge of the lower opening must be within 12” of the
floor (Figure 4).
• Each opening must have a free area of 1 square inch per 1000 BTU/hr input of all fuel burning appliances in the
boiler room. The minimum opening dimension is 3 inches. Minimum opening free area is 100 square inches per
opening.
• If the total volume of both the boiler room and the room to which the openings connect is less than 50 cubic feet per
1000 BTU/hr of total appliance input, install a pair of identical openings into a third room. Connect additional
rooms with openings until the total volume of all rooms is at least 50 cubic feet per 1000 BTU/hr of input.
• The “free area” of an opening takes into account the blocking effect of mesh, grills, and louvers. Where screens are
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