Bryant 369RAN III. Unconfined Space, Minimum Floor Area For Unconfined Space, IV. Confined Space

In addition to air needed for combustion, process air shall be provided as required for: cooling of equipment or material, controlling dew point, heating, drying, oxidation or dilution, safety exhaust, and odor control.

In addition to air needed for combustion, air shall be supplied for ventilation, including all air required for comfort and proper working conditions for personnel.

The barometric draft regulator (included with furnace) shall be installed in same room or enclosure as furnace in such a manner as to prevent any difference in pressure between regulator and combustion-air supply.

Air requirements for operation of exhaust fans, kitchen ventilation systems, clothes dryers, and fireplaces shall be considered in determining the adequacy of a space to provide combustion-air requirements.

The lack of a proper amount of combustion air can lead to serious furnace operational problems. Some of these problems are:

1.Excessive oil burner after-drip, and oil fumes.

2.Sooting.

3.Melted oil burner ignitor/relay control.

4.Air band or air turbulator settings more open than normal.

5.Lockouts on start-up. The requirements for combustion and ventilation air depend upon whether furnace is located in a CONFINED or UNCONFINED space.

III.UNCONFINED SPACE

An unconfined space must have at least 50 cu ft for each 1000 Btuh of total input for all the appliances (such as furnaces, clothes dryers, water heaters, etc.) in the space.

In unconfined spaces in buildings of conventional frame, brick, or stone construction, infiltration MAY be adequate to provide air for combustion, ventilation, and dilution of flue gases. This determi- nation must be made on an individual installation basis and must take into consideration the overall volume of unconfined space, the number of windows and ventilation openings, the number of doors to the outside, internal doors which can close off unconfined space, and overall tightness of building construction. Consideration must also be given to the amount of storage items (furniture, boxes, etc.) within the unconfined space which take away from the air volume. (Refer to Table 2.)

TABLE 2—MINIMUM FLOOR AREA

FOR UNCONFINED SPACE

369RAN FURNACE	MINIMUM SQ FT WITH
INPUT BTUH	7-1/2 FT CEILING
70,000	467
91,000	607
105,000	700
119,000	793
140,000	933
154,000	1026

Many new buildings and homes (and older ones that have been weatherized) MUST BE considered as being of tight construction, therefore, infiltration will not be sufficient to supply necessary air for combustion and ventilation.

A building can be considered as being of tight construction when:

1.Walls and ceilings exposed to outside atmosphere have a continuous water vapor retarder with a rating of 1 perm or less with openings gasketed or sealed, and/or

2.Weatherstripping has been added on operable windows and doors, and/or

3.Caulking or 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 fuel lines; and at other openings.

—4—

If combustion and ventilation air must be supplied to an uncon- fined space from outside, an opening with a FREE AREA of not less than 1 sq in. per 1000 Btuh of total input of all appliances within unconfined space (but not less than 100 sq in.) must be provided. This opening must be located such that it can not be blocked at any time.

IV. CONFINED SPACE

A confined space has a volume of less than 50 cu ft per 1000 Btuh of the total input rating for all appliances installed in that space.

When furnace is installed in a closet or enclosure, 2 ventilation openings, with OPEN AREA as dimensioned in example below are required for combustion air. The openings should be located about 6 in. from top and bottom of enclosure at front of furnace. (Refer to Table 3.)

TABLE 3—COMBUSTION AIR

FROM CONFINED SPACE

369RAN FURNACE	LENGTH	HEIGHT
INPUT BTUH	(IN.)	(IN.)
70,000-105,000	16	8
119,000	20	10

NOTE: In calculating free area, consideration shall be given to blocking effect of louvers, grilles, or screens protecting openings. Screens used shall not be smaller than 1/4 in. mesh and shall be readily accessible for cleaning. If free area through a louver or grille is known, it shall be used in calculating size and free area specified. If design and free area are not known, it may be assumed that wood louvers have 20 percent free area and metal louvers and grilles have 60 percent free area. Louvers shall be fixed in open position or interlocked with furnace so they open automatically at furnace start-up and remain open during furnace operation.

The size of the openings depends upon whether the air comes from outside of the structure or an unconfined space inside the structure.

A. All Air from Inside the Structure

For a confined space, where air is taken from an interior space, 2 permanent openings of equal area are required. One opening must be within 12 in. of ceiling and the other within 12 in. of floor. Each opening must have a free area of at least 1 sq in. per 1000 Btuh of total input rating but not less than 100 sq in. (Refer to Table 4.)

TABLE 4—COMBUSTION AIR

FROM UNCONFINED SPACE

369RAN FURNACE	FREE AREA PER
	OPENING
INPUT BTUH
	(SQ IN.)
70,000	100
91,000	100
105,000	105
119,000	119
140,000	140
154,000	154

B. All Air from Outside of Structure

If outside air is supplied to a confined space, then the 2 openings must be equal and located as above.

1.If combustion air is taken through a permanent opening directly communicating with the outdoors, the opening shall have a minimum free area of 1 sq in. per 4000 Btuh of total input rating for all equipment in the enclosure.

2.If combustion air is taken from outdoors through vertical ducts, the openings and ducts MUST have at least 1 sq in. of free area per 4000 Btuh of the total input for all equipment within the confined space. (Refer to Table 5.)