Miller CMF2 80 PG Instruction Manual download pdf (Page 16)

joint or union using a small paintbrush. If any bubbling is

observed, the connection is not sealed adequately and

must be retightened. Repeat the tightening and soap

check process until bubbling ceases.

IMPORTANT NOTE: When pressure testing gas supply

lines at pressures greater than 1/2 psig (14 inch W.C.),

the gas supply piping system must be disconnected

from the furnace to prevent damage to the gas control

valve. If the test pressure is less than or equal to 1/2

psig (14 inch W.C.), close the manual shut-off valve.

required that you measure the gas input rate. This may

be accomplished in the usual way, by clocking the gas

meter and using the local gas heating value. To check the

input of the furnace see page 21.

IMPORTANT NOTE: Observe the action of the burners

to make sure there is no yellowing, lifting or ﬂ ashback

of the ﬂ ame.

Converting to LP Gas

The CMF2 furnace is shipped from the factory for use with

natural gas but can be converted to use liquid propane

gas. Use the following procedure and Figure 12 (page 17)

for converting the gas burner.

1. Set thermostat to OFF.

2. Turn off all power to the furnace.

3. Open furnace door and locate the gas valve.

4. Push in on the gas knob and turn it to OFF.

5. Shut off gas supply at meter.

6. Disconnect gas burner electric cord, gas piping to

burner, and thermostat leads.

7. Remove nuts securing burner in place.

8. Disconnect inlet pipe union at burner.

9. Disconnect the two wires leading to gas control valve.

10. Remove bolts securing U-shaped manifold plate to

oriﬁ ce assembly.

11. Remove the main oriﬁ ce and replace it with the correct

LP fuel oriﬁ ce as shown in Table 4. Refer to the rating

plate on the furnace to determine the ﬁ ring rate for

your application. NOTE: If the ﬁ ring rate of your furnace

has been converted, make sure the appropriate LP

oriﬁ ce for the new ﬁ ring rate is installed.

12. Remove the regulator converter on top of the gas valve.

Invert the converter so that the red ring will be located

at the bottom and the LP stamping on the converter

appears up.

13. Screw converter back into the regulator, hand tight

plus 1/8 turn.

14. Reinstall the burner assembly into the furnace.

15. Reconnect the gas piping and electrical wires to the

gas valve.

16. Open the manual shut-off valve and follow the Operating

Instructions outlined on page 20.

High Altitude Application

Installation of this furnace at altitudes above 2,000 feet

shall be in accordance with local codes, or in the absence

of local codes, the National Fuel Gas Code, ANSI Z223.1/

NFPA 54 or National Standard of Canada, Natural Gas &

Propane Installation Code CGA B149.1. Please consult

your local code authority.

WARNING:

The reduction of input rating necessary for high

altitude installation may only be accomplished

with factory supplied oriﬁ ces. Do not attempt to

drill out oriﬁ ces in the ﬁ eld. Improperly drilled

oriﬁ ces may cause ﬁ re, explosion, carbon

monoxide poisoning, personal injury or death.

The CMF2 furnace is shipped from the factory with its

oriﬁ ces and gas regulator setting for natural gas operation

at sea level altitudes. At 2,000 feet, the NFGC requires

that this appliance be derated 4% for each 1,000 feet of

altitude. For example, the input needs to be reduced 8%

at 2,000 feet, 12% at 3,000 feet, etc. This deration is in

reference to the input rate and gas heating value at sea

level.

High altitude conversion for this furnace requires reducing

the oriﬁ ce size or decreasing the manifold pressure. When

decreasing the manifold pressure, the pressure must not

be set below 3.2 in WC. If the pressure needs to be set

below 3.2 in WC to achieve proper deration, then change

the oriﬁ ce size and raise the manifold pressure back to

3.5 in WC.

After changing the regulator pressure or the oriﬁ ces, it is

* Times are based on natural gas at an average of 1,000 BTU per cubic foot, a burner manifold pressure of 3.5 in WC, and a meter dial size of 1 cubic foot.

** Times are based on LP gas at an average of 2,500 BTU per cubic foot, a burner manifold pressure of 3.5 in WC, and a meter dial size of 1 cubic foot.

Table 4. Natural & LP Gas Oriﬁ ces

Burner

Designation

Firing Rate

Input (BTUH)

Natural Gas

Oriﬁ ce Number

Natural Gas

Time Per Rev.* (sec)

LP Gas

Oriﬁ ce

Number

LP Gas

Time Per Rev.** (sec)

Gas Gun-65-DI-S 65,000 24 55 43 138

Gas Gun-75-DI-S 75,000 20 48 40 120

Gas Gun-90-DI-S 85,000 18 43 37 106

1 2 ... 11 12 13 14 15 16 17 18 19 20 21 ... 31 32

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Miller CMF2 80 PG Instruction Manual Page 16

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