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AIR BALANCING
The Direct-Fired Gas, make-up heater requires the correct air flow velocity across the burner. The burner profile opening creates a pressure drop which increases the air velocity across the burner. The air flow switch monitors the pressure difference, and will open the burner circuit if pressure difference is not correct. The air flow switches have low and high pressure settings. The pressure drop should not be near the minimum and maximum of the air flow switch. Balancing may be required to fine tune the burner profile pressure drop. The air flow pressure drop should be checked in fresh and return air modes on the re-circulating heaters. See the specifications and instructions below on air balancing a re-circulating heater.
Unit Type
Re-circulating
Air Flow
Switch
Part Number
DDP-106-256
Low
Setting
In. W.C.
0.15”
High
Setting
In. W.C.
0.95”
Target Pressure
Drop In. W.C.
Natural Gas
0.4
5” – 0.65”
Target Pressure
Drop In. W.C.
Propane Gas
0.4
5” – 0.65”
The pressure drop should be checked with the burner off or operating at 70 degree discharge if ambient temperature is less than 65 degrees. Read the pressure drop at the extra probes supplied with the blower ON. This should be repeated in fresh and return air modes.
WARNING!!
Disconnect power and close all gas valves before and while making burner profile adjustments.
The heater ’s profile and damper openings are sized to the units designed airflow. While balancing the unit to jobsite static pressures the profile and damper blank-off plates may need to be moved to achieve the correct air flow pressure drop.
If the pressure drop is too high, in fresh and return air mode, remove or adjust the bypass fresh air and return air damper blank-off panels, which will decrease the pressure drop. If the correct air flow pressure drop is still not achieved adjust the blower drives to decrease the blowers RPM.
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If the pressure drop is too low, in fresh and return air mode, add more blank-off panels to the burner profile opening and bypass fresh air and return air damper, which will increase the pressure drop. (There must be at least 2 inches of area minimum around the burner.) If the correct air flow pressure drop is still not achieved adjust the blower drives to increase the blowers RPM.
If the pressure drop is too high, in fresh mode only, remove or adjust the bypass damper blank-off panels, which will decrease the pressure drop. The return air damper opening may need to be adjusted to maintain the correct air flow pressure drop when switching back to return air mode.
If the pressure drop is too high, in return air mode only, remove or adjust the return air damper and burner profile opening blank-off panels, and add the blank-off panels to the bypass damper, which will decrease the pressure drop.
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