Bryant 340MAV instruction manual Altitude Derate Multiplier, United States, Canada

EXAMPLE: (0—2000 ft altitude using Table 9)

Heating value = 1050 Btu/cu ft

Specific gravity = 0.62

Therefore: Orifice No. 45

Manifold pressure 3.6-in. wc

*Furnace is shipped with No. 45 orifices. In this example all main burner orifices are the correct size and do not need to be changed to obtain the proper input rate.

Check and verify burner orifice size in furnace. NEVER ASSUME ORIFICE SIZE; ALWAYS CHECK AND VERIFY.

2. Adjust manifold pressure to obtain input rate.

NOTE: Manifold pressure must always be measured with burner enclosure front REMOVED. Gas meter must always be clocked with burner enclosure front INSTALLED.

a.Remove burner enclosure front.

b.Remove cap that conceals adjustment screw for gas valve regulator. (See Fig. 50.)

c.Jumper R and W thermostat connections on control to start furnace operation.

d.Turn adjusting screw, counterclockwise (out) to decrease manifold pressure or clockwise (in) to increase manifold pressure.

NOTE: This furnace has been approved for a manifold pressure of 3.2 in. wc to 3.8 in. wc when installed at altitudes up to 2000 ft. For altitudes above 2000 ft, the manifold pressure can be adjusted from 2.0 in. wc to 3.8 in. wc. If manifold pressure is outside this range, change burner orifices to obtain pressure in this range.

CAUTION: DO NOT bottom out gas valve regulator adjusting screw. This can result in unregulated manifold pressure and result in excess overfire and heat exchanger failures.

NOTE: If orifice hole appears damaged or it is suspected to have been redrilled, check orifice hole with a numbered drill bit of correct size. Never redrill an orifice. A burr-free and squarely aligned orifice hole is essential for proper flame characteristics.

e.Replace gas valve regulator adjustment screw cap.

f.Replace burner enclosure front and verify adjusted gas input rate using method outlined in item 3.

g.Look through sight glass in burner enclosure and check burner flame. Burner flame should be clear blue, almost transparent. (See Fig. 52.)

h.Remove jumper from R and W.

BURNER FLAME

BURNER

MANIFOLD

A89020

Fig. 52—Burner Flame

—43—

TABLE 11—ALTITUDE DERATE MULTIPLIER

ALTITUDE	% OF	DERATE MULTIPLIER
(FT)	DERATE	FACTOR FOR U.S.A.*
0—2000	0	1.00
2001—3000	4—6	0.95
3001—4000	6—8	0.93
4001—5000	8—10	0.91
5001—6000	10—12	0.89
6001—7000	12—14	0.87
7001—8000	14—16	0.85
8001—9000	16—18	0.83
9001—10,000	18—20	0.81

* Derate multiplier factor is based on midpoint altitude for altitude range.

3. Verify natural gas input rate by clocking gas meter.

NOTE: Be sure all pressure tubing, combustion-air and vent pipes, and burner enclosure front are in place when checking input by clocking gas meter.

a.Calculate high-altitude adjustment (if required).

UNITED STATES

At altitudes above 2000 ft, this furnace has been ap- proved for a 2% derate for each 1000 ft above sea level. See Table 11 for derate multiplier factor.

EXAMPLE: 100,000 BTUH INPUT FURNACE INSTALLED AT 4300 FT.

Furnace Input Rate		Derate		Furnace Input Rate
	X	Multiplier	=	at Installation
at Sea Level
		Factor		Altitude
100,000	X	0.91	=	91,000

CANADA

At installation altitudes from 2000 to 4500 ft, this furnace must be derated 5% by an authorized Gas Conversion Station or Dealer. To determine correct input rate for altitude, see example above and use 0.95 as derate multiplier factor.

b.Reinstall burner box cover.

c.Gas valve regulator seal cap MUST be installed.

d.Turn off all other gas appliances and pilots.

e.Start furnace and let operate for 3 minutes.

f.Measure time (in sec) for gas meter test dial to complete

1revolution.

g.Refer to Table 12 for cu ft of gas per hr.

h.Multiply gas rate (cu ft/hr) X heating value (Btu/cu ft) using natural gas heating value from local gas utility/supplier.