Thomas & Betts UDAP, UDAS dimensions High Altitude Operation, Clearances, Pressure Switch

7.High Altitude Operation

Gas valve adjustment for high altitude can only be done after heater is operating; see Paragraph 12.

If the heater is being installed at an elevation above 2000 ft (610M), the input rate will have to be derated. This is done by adjusting the valve outlet pressure.

In addition, if the heater is being installed at an altitude above 6000 ft (1830M), the pressure switch will have to be changed. If ordered with the unit as Option DJ20 or DJ21, the pressure switch is shipped separately.

Adjusting the valve outlet pressure is done after the heater is in operation; follow the instructions in Paragraph 12. Capacities and inputs for derated units are also listed in Paragraph 12.

If the pressure switch needs to be changed, do that before the heater is operated; follow the instructions in FIGURE 4.

FIGURE 4 - Installing High Altitude Pressure Switch required above 6000 ft (1830M) elevation

Model UDAP

Size	30	45	60	75	100	125			150	175	200	225	250	300	350	400
High Altitude Switch P/N	197031			197032		197031						201160			201161
Negative Pressure OFF Setpoint "w.c.	0.35			0.45				0.35				1.00			1.30
Label color	Purple			Pink			Purple					Brown			White
Model UDAP-CV with Option AV6 for Common Venting
Size	30	45	60	75	100
High Altitude Switch P/N	197029	197032	196362		196388
Negative Pressure OFF Setpoint "w.c.	0.60	0.45	0.55		0.50
Label color	Lt Blue	Pink	White		Orange
Model UDAS
Size	30	45	60	75	100	125			150	175	200	225	250	300	350	400
High Altitude Switch P/N		197029			196388	197030			197031			201160			201161
Differential Pressure OFF Setpoint "w.c.		0.60			0.50	0.40			0.35			1.00			1.30
Label color		Lt. Blue			Orange		Green		Purple			Brown			White

Instructions for Changing Pressure Switch

1.	In the control compartment, locate the pressure switch.
	Sizes 30-125 - On the back wall of the control compartment.
	Sizes 150-400 - On the bracket on the bottom of the control compartment.
2.	Mark and disconnect the two wires attached to the pressure switch.
3.	Disconnect the sensing tube from the pressure switch.
4.	Locate the two screws holding the switch mounting bracket. Remove the
Pressure Switch	screws (save screws) and the pressure switch.
5.	Using the same screws, install the high altitude pressure switch. Attach the
	sensing tube and wires.

8. Clearances

Units 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 construction. 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 tempera- ture of 90°F above the surrounding ambient temperature is not exceeded.

Clearances

Size	Top		Flue Connector		Access Panel		Non-Access Side		Bottom*		Rear
	inches	mm	inches	mm	inches	mm	inches	mm	inches	mm	inches	mm
30-125	1	25	6	152	18	457	1	25	1	25	18	457
150-400	4	102	6	152	18	457	2	51	1	25	18	457

*Suspend the heater so that the bottom is a minimum of 5 feet (1.5M) above the floor.

Form RZ-NA I-UDA, Mfg #195673 Rev 5, Page 7