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Table 5 - Main Burner Orifi ce Schedule*

PRIMARY AIR SHUTTER ADJUSTMENT

After the unit has been operating for at least 15
minutes, adjust the primary air flow to the burners.
Turn the friction-locked, manually-rotated air shutters
clockwise to close, or counterclockwise to open (see
Figures 11, 12, 14 and 16).

For correct air adjustment, close

the air shutter until yellow tips in the flame
appear. Then open the air shutter to the point
just beyond the position where yellow tipping
disappears. Refer to Figure 12 .

NOTICE: There may be momentary and spasmodic
orange flashes in the flame. This is caused by the
burning of airborne dust particles, and not to be
confused with the yellow tipping, which is a stable
or permanent situation when there is insufficient
primary air.

Figure 12 - Main Burner Flames

GAS INPUT RATE

Check the gas input rate as follows

(Refer to general

safety section for metric conversions/SI units):

Never overfire the unit heater,

as this may cause unsatisfactory operation or
shorten the life of the heater.

1. Turn off all gas appliances that use gas through the

same meter as the unit heater.

2. Turn gas on to the unit heater.
3. Clock the time in seconds required to burn one

cubic foot of gas by checking the gas meter.

4. Insert the time required to burn one cubic foot of

gas into the following formula and compute the
input rate.

3600 (Sec. Per Hr.) x Btu/Cu. Ft

= Input Rate
Time (Sec.)

For example, assume the Btu content of one cubic foot
of gas equalled 1000 and that it takes 18 seconds to
burn one cubic foot of gas.

3600 x 1000

= 200,000 Btu/Hr.

NOTICE: If the computation exceeds or is less
than 95 percent of the gas Btu/hr. input rating (see
Specifi cations), adjust the gas pressure.

GAS PRESSURE ADJUSTMENTS

Adjust the gas pressure as follows:
1. NATURAL GAS: Optimum results are obtained when

the unit heater is operating at its full input rating with
the manifold pressure of 3.5 inches W.C. (0.9 kPa).
Adjustment of the pressure regulator is not normally
necessary since it is preset at the factory. However,
fi eld adjustment may be made as follows:
(a.) Attach manometer at pressure tap plug adjacent

to the control outlet.

(b.) Remove regulator adjustment screw cap,

located on combination gas valve.

(c.) With a small screwdriver, rotate the adjustment

screw counterclockwise to decrease or clock-
wise to increase pressure. Do not force beyond
stop limits.

(d.) Replace regulator adjustment screw cap.

2. PROPANE GAS: An exact manifold pressure of 10.0

inches W.C. (2.5 kPa) must be maintained for proper
operation of the unit heater. If the unit is equipped
with a pressure regulator on the combination gas
valve, follow steps “a” through “d” above. If the unit
is not so equipped, the propane gas supply system
pressure must be regulated to attain this manifold
operating pressure.

3. The adjusted manifold pressure should not vary

more than 10% from the pressure specified in
Table 5.

INPUT

1000

BTU

2500 BTU/Ft

(93.1 MJ/m

)

PROPANE

TYPE OF GAS

NATURAL

HEATING VALUE

1075 BTU/Ft

(40.1 MJ/m

)

3.5" W.C.

(0.87kPA)

0" W.C.

(2.49 kPA)

NO. OF

BURNER

ORIFICES

MANIFOLD

PRESSURE

* This schedule is for units operating at normal altitudes of 2000 ft. (610m) or
less. SPECIAL ORIFICES ARE REQUIRED FOR INSTALLATIONS ABOVE
2,000 FT. (610M).

When installed in Canada, any references to deration at altitudes in excess of
2000 feet (610m) are to be ignored. At altitudes of 2000 to 4500 feet (610 to
1372m), the unit heaters must be orifi ced to 90% of the normal altitude rating,
and be so marked in accordance with the ETL certifi cation.