Desa VS24NRA AIR for Combustion Ventilation, Determining FRESH-AIR Flow for Heater Location

OWNER’S MANUAL

AIR FOR

COMBUSTION AND

VENTILATION

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DETERMINING FRESH-AIR FLOW FOR HEATER 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 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 20 ft. (length) x 16 ft. (width) x 8 ft. (ceiling height) = 2560 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: 2560 cu. ft. (volume of space) ÷ 50 cu. ft. = 51.2 or 51,200 (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	Example:
Gas furnace		______________ Btu/Hr
			Gas water heater		40,000	Btu/Hr
Vented gas heater		______________ Btu/Hr
			Vent-free heater	+	33,000	Btu/Hr
Gas fireplace logs		______________ Btu/Hr
			Total	=	73,000	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: 51,200 Btu/Hr (maximum the space can support) 73,000 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 worksheet, 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 heater, 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 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, ANS Z223.1, 1992, Section 5.3 or applicable local codes.

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