Thomas & Betts LDAP 1200 warranty Combustion Air, Clearances inches/mm

8. Clearances

Heaters must be installed so that the clearances in the table are provided for combus- tion air space, inspection and service, and for proper spacing from combustible con- struction. Clearance to combustibles is defined as the minimum distance from the heater to a surface or object that is necessary to ensure that a surface temperature of 90°F above the surrounding ambient temperature is not exceeded.

Clearances - inches/mm

Size	Top		Flue		Front		Rear		Disconnect		Side		Bottom
			Connector		(Access Panel)				Side
	inches	mm	inches	mm	inches	mm	inches	mm	inches	mm	inches	mm	inches	mm
400	12	305	6	152.4	18	457	2	50.8	18	457	2	50.8	60	1524
800	12	305	6	152.4	18	457	2	50.8	18	457	2	50.8	60	1524
1200	12	305	6	152.4	18	457	2	50.8	18	457	2	50.8	60	1524

9.Combustion Air

FIGURE 2 - Definition of Confined Space and Required Openings for Combustion Air

Confined Space:

A space whose volume is less than 50 cubic feet per 1000 BTUH of the installed appliance input rating

(3) (1) (2)

Confined

Space

(3) (1) (2)

This heater must be supplied with the air that enters into the combustion process and is then vented to the outdoors. Sufficient air must enter the equipment location to replace that exhausted through the heater vent system. In the past, the infiltration of outside air assumed in heat loss calculations (one air change per hour) was assumed to be sufficient. However, current construction methods using more insulation, vapor barriers, tighter fitting and gasketed doors and windows, weather-stripping, and/or mechanical exhaust fans may now require the introduction of outside air through wall openings or ducts.

The requirements for combustion and ventilation air depend upon whether the heater is located in a confined or unconfined space. An "unconfined space" is defined as a space whose volume is not less than 50 cubic feet per 1000 BTUH of the installed appliance. Under ALL conditions, enough air must be provided to ensure there will not be a negative pressure condition within the equipment room or space.

WARNING: A Model LDAP power-vented heater is designed to take combustion air from the space in which the heater is installed and is not designed for connection to outside combustion air intake ducts. Connecting outside air ducts voids the warranty and could cause hazardous operation. See Hazard Levels, page 2.

Combustion Air Requirements for a Heater Located in a Confined Space

Do not install a heater in a confined space without providing wall openings leading to and from the space. Provide openings near the floor and ceiling for ventilation and air for combustion as shown in FIGURE 2, depending on the combustion air source as noted in Items 1, 2, and 3 below.

Add total BTUH of all appliances in the confined space and divide by figures below for square inch free area size of each (top and bottom) opening.

1.Air from inside the building - openings 1 square inch free area per 1000 BTUH. Never less than 100 square inches free area for each opening. See (1) in FIGURE 2.

2.Air from outside through duct - openings 1 square inch free area per 2000 BTUH. See (2) in FIGURE 2.

3.Air direct from outside - openings 1 square inch free area per 4000 BTUH. See

(3) in FIGURE 2.

NOTE: For further details on supplying combustion air to a confined space, see the National Fuel Gas Code ANSI Z223.1a (latest edition).

Form RZ-NA-I-LDAP, P/N 207733 (Rev 2), Page 6