The Effect Of Elevation On Oil Burner Firing

The elevation of the installation of a modern high-speed flame retention oil burner affects the performance of the burner. Allowance for elevation must be taken into consideration when choosing an oil burner and operating it above 2000 feet.

It is especially important in high elevation installations to adjust air settings to match the burner nozzle firing rate. As elevation increases above sea level, the ambient air contains less oxygen. Because there is less available oxygen per cubic foot of air, the burner must deliver a greater volume flow (CFM) of air to provide the proper amount of oxygen for the amount of oil being burned. This is the reason that an increase in the burner air setting may be required.

It is also important in high elevation installations to consider the maximum firing rate of the burner, so that the heat input as required by the application and as recommended by the boiler or furnace manufacturer is maintained. Regardless of elevation, the oil burner has a maximum volume flow of air that it can deliver. As a result, the maximum firing rate of the oil burner decreases as the elevation increases, because the combustion air contains less oxygen. An increase in the size of a fixed-type retention head, an adjustment of the head position of a variable-type head (to a higher or more open position), or even the use of an oil burner with a higher maximum firing rate may be necessary.

Note that this re-rating is not de-rating. This Bulletin addresses re-rating of the burner, not de-rating of the heating appliance. The firing rate (amount of BTU input) of the burner must be maintained to meet the heating load that the appliance has been sized to meet. If a heating appliance is de-rated by reducing the firing rate of the oil burner (as is sometimes done to increase efficiency), the BTU output of the appliance may not be adequate to meet the heating load of the installation.

The effect of elevation up to 2000 feet is minimal, so no re-rate is necessary up to 2000 feet elevation. Above 2000 feet, for every 1000 feet above sea level (including the first 2000 feet), there is a 1.84% rate reduction of the burner. To assist you, we have included the following chart and some examples:
NOTE: All examples are for 7000′ elevation.
1.84% x 7 (for 7000 ft.) = 12.9% > 100% – 12.9% = 87.1%

Elevation
Burner Rating, GPH
 0′0.751.001.251.501.752.002.252.502.753.003.504.004.505.00
500′0.751.001.251.501.752.002.252.502.753.003.504.004.505.00
1000′0.751.001.251.501.752.002.252.502.753.003.504.004.505.00
1500′0.751.001.251.501.752.002.252.502.753.003.504.004.505.00
2000′0.751.001.251.501.752.002.252.502.753.003.504.004.505.00
2500′0.720.951.191.431.671.912.152.392.622.863.343.824.294.77
3000′0.710.941.181.421.651.892.132.362.602.833.313.784.254.72
3500′0.700.941.171.401.641.872.112.342.572.813.273.744.214.68
4000′0.690.931.161.391.621.852.082.322.552.783.243.714.174.63
4500′0.690.921.151.381.611.832.062.292.522.753.213.674.134.59
5000′0.680.911.141.361.591.822.042.272.502.723.183.634.094.54
5500′0.670.901.121.351.571.802.022.252.472.703.153.604.044.49
6000′0.670.891.111.331.561.782.002.222.452.673.113.564.004.45
6500′0.660.881.101.321.541.761.982.202.422.643.083.523.964.40
7000′0.650.871.091.311.521.741.962.182.402.613.053.483.924.36
7500′0.650.861.081.291.511.721.942.162.372.593.023.453.884.31
8000′0.640.851.071.281.491.711.922.132.352.562.983.413.844.26
9000′0.630.831.041.251.461.671.882.092.292.502.923.343.754.17
10000′0.610.821.021.221.431.631.842.042.242.452.863.263.674.08

Example 1: Rating of the Maximum Firing Rate for Burners @7000′

Burner ModelMaximum Firing Rate of
Burner @ Sea Level
XElevation Re-rate
Factor @ 7000ft.
=Adjusted Maximum
Firing Rate
AFG3.00 gphX87.1%=2.61 gph
AF3.00 gphX87.1%=2.61 gph
AFII 1501.50 gphX87.1%=1.31 gph
AFII 850.85 gphX87.1%=0.74 gph
SF5.50 gphX87.1%=4.79 gph
SR2.00 gphX87.1%=1.74 gph
CF3753.75 gphX87.1%=3.27 gph


TO PROVIDE ADEQUATE OXYGEN IN THE COMBUSTION AIR TO MAINTAIN THE FIRING RATE FOR THE HEATING LOAD:
If after the re-rate factor is used the required firing rate input exceeds the Adjusted Maximum Firing Rate for the burner model being applied, a burner model with a higher Adjusted Maximum Firing Rate will be required.

For this example: If an appliance operating at 7000 ft. elevation requires a firing rate input of 2.75 gph, an SF or CF375 burner may be required instead of an AFG burner.

Example 2: Re-rating of the Maximum Firing Rate for Fixed-Type Burner Head @7000′

Burner ModelHeadMaximum Firing
Rate of Head
XElevation Re-rate
Factor @ 7000ft.
=Adjusted Maximum
Firing Rate of Head
AFGF31.25 gphX87.1%=1.09 gph
AFGF61.65 gphX87.1%=1.44 gph
AFGF122.00 gphX87.1%=1.74 gph
AFGF222.50 gphX87.1%=2.18 gph
AFGF313.00 gphX87.1%=2.61 gph
AFGL11.10 gphX87.1%=0.96 gph

 

TO PROVIDE ADEQUATE OXYGEN IN THE COMBUSTION AIR TO MAINTAIN THE FIRING RATE FOR THE HEATING LOAD:
If after the re-rate factor is used the required firing rate input exceeds the Adjusted Maximum Firing Rate for the burner head being applied, a burner head with a higher Adjusted Maximum Firing rate may be required.

For this example: If an AFG burner operating at 7000ft. elevation requires a firing rate input of 1.15 gph, an F6 head may be required instead of an F3 head.

Example 3: Re-rating of the Maximum Firing Rate for Adjustable-Type Burner Head Setting @7000′

Burner ModelHeadHead
Setting
Max. Firing Rate
at Head Setting
XElevation Re-rate
Factor
=Adjusted Max. Firing
Rate at Head Setting
AFGV111.50 gphX87.1%=1.31 gph
AFGV121.75 gphX87.1%=1.52 gph
AFGV132.25 gphX87.1%=1.96 gph
AFGV142.50 gphX87.1%=2.18 gph
AFGV152.75 gphX87.1%=2.40 gph


TO PROVIDE ADEQUATE OXYGEN IN THE COMBUSTION AIR TO MAINTAIN THE FIRING RATE FOR THE HEATING LOAD:
If after the re-rate factor is used the required firing rate input exceeds the Adjusted Maximum Firing Rate for the head setting, a head setting for a higher Adjusted Maximum Firing rate may be required.

For this example: If an AFG burner using a V1 head operating at 7000ft. elevation requires a firing rate input of 1.40 gph, a change of head setting from 1 to 2 may be required.

Example 4: Re-rating of the Maximum Firing Rate for Adjustable-Type Burner Head Setting @7000′

Burner ModelHeadHead
Setting
Max. Firing Rate
at Head Setting
XElevation Re-rate
Factor
=Adjusted Max. Firing
Rate at Head Setting
CF375SL101.65 gphX87.1%=1.44 gph
CF375SL111.75 gphX87.1%=1.52 gph
CF375SL132.00 gphX87.1%=1.74 gph
CF375SL142.50 gphX87.1%=2.18 gph
CF375SL153.00 gphX87.1%=2.61 gph
CF375SL163.75 gphX87.1%=3.27 gph

NOTE: The above settings are approximate, and can vary depending on actual job conditions and overfire pressure.

TO PROVIDE ADEQUATE OXYGEN IN THE COMBUSTION AIR TO MAINTAIN THE FIRING RATE FOR THE HEATING LOAD:
If after the re-rate factor is used the required firing rate input exceeds the Adjusted Maximum Firing Rate for the head setting, a head setting for a higher Adjusted Maximum Firing rate may be required.

For this example: If a CF375 burner using an SL1 head operating at 7000 ft. elevation requires a firing rate input of 2.25 gph, a change of head setting from 4 to 5 may be required.

REMEMBER: It is important to maintain the BTU input as required by the installation and specified by the furnace or boiler manufacturer.