Allied Air Enterprises Burner Orifice Sizing, TABLE Burner Orifice Selection, Natural, Propane

Burner Orifice Sizing:

The furnace is supplied with standard orifices for the gas shown on the rating plate. Table 6 shows combinations of heating values and specific gravities for various gases, from which proper input can be obtained.

If changing orifices is required, remove the manifold from the furnace (following the instructions found on page

24)and replace orifices as required by Table 6, the altitude derating section of this instruction or as local code dictates.

TABLE 6

Burner Orifice Selection

Type of Gas@Manifold Press.		Orifice
(Heating Value-Specific Gravity)		Size
	Btu per Cu. Ft.	(Drill #)
Natural	Manifold Press.= 3.5"w.c.
	800-0.6	40
	900-0.6	41
	1000-0.6	42
	1100-0.6	43
Propane	Manifold Press.= 10"w.c.
	2500-1.53	54

After securing the manifold assembly, replace all other components and/or wiring, being sure that all connections and screws are tightened properly.

Altitude Derating:

The following information is provided as guidelines for altitude derating and is not meant to supersede any state or local codes. Local codes have priority over any others and in some case might limit your options in dealing with an altitude derate situation.

NOTE: In Canada for altitudes up to 4500 ft. (1372 m) see the rating label on this furnace for proper manifold pressure and orifice size. Certification for installations at altitudes over 4500 ft. (1372 m) is the jurisdiction of local authorities.

Check with your local gas company to find out if the gas supply in your area is derated. Gas deration negates the necessity of performing any adjustment on the furnace.

If your gas supply is not derated, regardless of the type of gas used, installation of this furnace at elevations above 2,000 ft. requires an input reduction at the rate of four percent (4%) for each 1,000 ft. above sea level.

Unless an orifice change is specified by an applicable code, the recommended method of altitude derating this furnace is to appropriately lower your manifold pressure. The appropriate manifold pressures based on the elevation and the heating value can be found in Table 7.

TABLE 7

High Altitude Manifold Pressure Derate

(with standard 42 orifice Natural / 54 orifice LP sizes)

Altitude		*Heating Value of Natural Gas						LP
				(BTU/FT3)				Propane
(Feet)
	900		950		1000	1050	1100	2500
0-999	4.32		3.88		3.50	3.16	2.84	10
1000-1999	4.32		3.88		3.50	3.16	2.84	10
2000-2999	3.67		3.29		2.97	2.68	2.41	8.46
3000-3999	3.38		3.04		2.74	2.47	2.22	7.74
4000-4999	3.11		2.79		2.52	2.27	2.04	7.05

*Heating-Value based on atmospheric pressure of 30 inhg and 60°F temperature.

If local codes require an orifices change the appropriate orifice size based on the elevation and the heating value can be found in Table 8. Sizing of the orifice must be based on the previously mentioned 4% derate for each 1,000 feet for installations at/or above 2,000 feet rule and the orifices must be drilled in such a way as to assure concentricity. Hand drilling of orifices

is unacceptable.

TABLE 8

High Altitude Orifice Size Derate

Altitude		*Heating Value of Natural Gas					LP
				(BTU/FT3)			Propane
(Feet)
	900		950	1000	1050	1100	2500
2000-2999	N.C.		N.C.	43	43	44	N.C.
3000-3999	N.C.		N.C.	43	44	44	N.C.
4000-4999	43		43	44	44	45	55

*Heating-Value based on atmospheric pressure of 30 inhg and 60°F temperature.

Hand drilling of orifices is never acceptable since it could lead to delayed ignition, overfiring, improper combustion, flashback and flame rollout. All these conditions could lead to a fire hazard and bodily harm, or loss of life.

Blower Adjustment Checkout:

This furnace is equipped with a variable speed circulation air blower motor that will deliver a constant airlfow within a wide range of external static pressures. The unit as shipped is factory set to run at the middle of the heating rise range as shown on the unit rating plate.

For low heat to high heat transition the control changes the blower speed from low heat speed to high heat speed. Check the temperature rise between the return and supply plenums to make sure it is within the rise range shown on the rating plate.

Heat blower off delay is a fixed 180 second delay. After the 180 second delay the motor will slowly ramp down to a soft stop. N0 adjustments need to be made in the heating mode.

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