Empire Comfort Systems 31)L(N, VFP36FP, VFP32FP, P)-1, 21)L(N Unusually Tight Construction

WATER VAPOR: A BY-PRODUCT OF UNVENTED ROOM HEATERS

Water vapor is a by-product of gas combustion. An unvented room heater produces approximately one (1) ounce (30ml) of water for every 1,000 BTU's (.3KW's) of gas input per hour.

Unvented room heaters are recommended as supplemental heat (a room) rather than a primary heat source (an entire house). In most supplemental heat applications, the water vapor does not create a problem. In most applications, the water vapor enhances the low humidity atmosphere experienced during cold weather.

The following steps will help insure that water vapor does not become a problem.

1.Be sure the heater is sized properly for the application, including ample combustion air and circulation air.

2.If high humidity is experienced, a dehumidifier may be used to help lower the water vapor content of the air.

3.Do not use an unvented room heater as the primary heat source.

PROVISIONS FOR ADEQUATE COMBUSTION & VENTILATION AIR

This heater shall not be installed in a confined space or unusually tight construction unless provisions are provided for adequate combustion and ventilation air.

The National Fuel Gas Code,ANSI Z223.1 defines a confined space as a space whose volume is less than 50 cubic feet per 1,000 Btu per hour (4.8m3 per kw) of the aggregate input rating of all appliances installed in that space and an unconfined space as a space whose volume is not less than 50 cubic feet per 1,000 Btu per hour (4.8m3 per kw) of the aggregate input rating of all appliances installed in that space. Rooms communicating directly with the space in which the appliances are installed, through openings not furnished with doors, are considered a part of the unconfined space.

Unusually Tight Construction

The air that leaks around doors and windows may provide enough fresh air for combustion and ventilation. However, in buildings of unusually tight construction, you must provide additional fresh air.

Unusually tight construction is defined as construction where:

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

b.Weather-stripping has been added on openable windows and doors, and

c.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 gas lines, and at other openings.

If your home meets all of the three criteria above, you must provide additional fresh air. See “Ventilation Air From Outdoors,” page 8.

Determining if You Have a Confined or Unconfined Space Use this worksheet to determine if you have a confined or unconfined space.

Space: Includes the room in which you will install heater plus any adjoining rooms with doorless passageways or ventilation grills between the rooms.

1. Determine the volume of the space (length x width x height).

Length x Width x Height =cu. ft. (volume of space)

Example: Space size 16 ft. (length) x 10 ft. (width) x 8 ft. (ceiling height) = 1,280 cu. ft. (volume of space)

If additional ventilation to adjoining room is supplied with grills or openings, add the volume of these rooms to the total volume of the space.

2.Divide the space volume by 50 cubic feet to determine the maximum BTU/Hr the space can support.

(volume of space) ÷ 50 cu. ft. = (maximum BTU/Hr the space can support)

Example: 1,280 cu. ft. (volume of space) ÷ 50 cu. ft. = 25.6 or 25,600 (maximum BTU/Hr the space can support)

3. Add the BTU/Hr of all fuel burning appliances in the space.

Vent-free heater			BTU/Hr
Gas water heater			BTU/Hr
Gas furnace			BTU/Hr
Vented gas heater			BTU/Hr
Gas fireplace logs			BTU/Hr
Other gas appliances*	+		BTU/Hr
Total	=		BTU/Hr
Example: Vented gas heater		20,000	BTU/Hr
Vent-free heater		+ 18,000	BTU/Hr
Total	=	38,000	BTU/Hr

*Do not include direct-vent gas appliances. Direct vent draws combustion air from the outdoors and vents to the outdoors.

4.Compare the maximum BTU/Hr the space can support with the actual amount of BTU/Hr used.

BTU/Hr (maximum the space can support)

BTU/Hr (actual amount of BTU/Hr used)

Example:

25,600 BTU/Hr (maximum the space can support)

38,000 BTU/Hr (actual amount of BTU/Hr used)

Warning: If the area in which the heater may be operated is smaller than that defined as an unconfined space or if the building is of unusually tight construction, provide adequate combustion and ventilation air by one of the methods described in the National Fuel Gas Code, ANSI Z223.1, Section 5.3 or applicable local codes.

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