Desa FB36NCA, FB42NC, FB36CA, FB42C manual

OWNER’S MANUAL

AIR FOR

COMBUSTION AND

VENTILATION

Continued

DETERMINING AIR FLOW FOR FIREBOX LOCATION

Determining if You Have a Confined or Unconfined Space

Use this work sheet to determine if you have a confined or unconfined space.

Space: Includes the room in which you will install firebox 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 22 ft. (length) x 18 ft. (width) x 8 ft. (ceiling height) = 3168 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: 3168 cu. ft. (volume of space) ÷ 50 cu. ft. = 63.3 or 63,300 (maximum Btu/Hr the space can support)

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

Vent-free firebox	____________	Btu/Hr	Example:
Gas water heater*	____________	Btu/Hr
			Gas water heater		40,000	Btu/Hr
Gas furnace	____________	Btu/Hr
			Vent-free firebox
Vented gas heater	____________	Btu/Hr		+
			with log heater		39,000	Btu/Hr
Gas firebox logs	____________	Btu/Hr
				=
			Total		79,000	Btu/Hr
Other gas appliances* + ____________ Btu/Hr

Total	= ____________	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: 63,300 Btu/Hr (maximum the space can support) 79,000 Btu/Hr (actual amount of Btu/Hr used)

The space in the above example is a confined space because the actual Btu/Hr used is more than the maximum Btu/Hr the space can support. You must provide additional fresh air. Your options are as follows:

A.Rework work sheet, adding the space of an adjoining room. If the extra space provides an unconfined space, remove door to adjoin- ing room or add ventilation grills between rooms. See Ventilation Air from Inside Building, page 6.

B.Vent room directly to the outdoors. See Ventilation Air from Outdoors, page 6.

C.Install a lower Btu/Hr firebox, if lower Btu/Hr size makes room unconfined.

If the actual Btu/Hr used is less than the maximum Btu/Hr the space can support, the space is an unconfined space. You will need no additional fresh air ventilation.

WARNING: If the area in which the firebox and gas log heater may be operated is smaller than that defined as an unconfined space, provide adequate combustion and ventillation air by one of the methods described in the National Fuel Gas Code, ANSI Z223.1, 1992, Section 5.3 or applicable local codes.

Continued

103451