Commercial Products  > Commercial Systems
Modulating Combustion Air System X

The ENERVEX MCASx Modulating Combustion Air Supply System takes the guesswork out of challenges such as: How much air is required for proper combustion? What if someone in the boiler room closes a window and cuts off adequate air supply to an individual boiler or the mechanical room in general? Can I reduce the number or size of air intake louvers needed?


  • This demand-controlled air supply system optimizes any heating appliance’s efficiency
  • Controls the supply of combustion air to individual boilers – or to the mechanical room in general.
  • Designed for commercial boilers and water heaters - and for process applications
  • Fully packaged, compact system consisting of a variable-speed supply fan and monitoring controls that regulate air supply by modulating the fan speed.
  • Integrated safety system


  • Direct or indirect air supply offers flexibility
  • Premium efficiency motor reduces excess air supply & saves fuel
  • Provides perfect combustion air supply at all firing rates
  • Includes operating controllers with code-required safety interlocks
  • Supplies combustion air independently of boiler room location
  • Less maintenance, longer equipment life
  • Aesthetically attractive; no standard gravity louvers needed

The MCAS system consists of an air supply fan, BEF, Box Ventilator and the EBC31, Modulating Fan Control. The EBC31 maintains a constant pressure in the mechanical room where the heating appliances are installed by modulating the speed of the supply fan. The MSC EDrive Motor Speed Control is also part of the system.

Each appliance is interlocked with the control. A call for heat activates the supply fan and releases the burner once the pre-set room pressure is established. The sequence is repeated every time a new heating appliance calls for heat. When an appliance shuts down, the fan will slow down while still maintaining the pressure setting. When the last appliance shuts down the supply fan will operate in post-purge mode for a preset time period.

The integrated proven pressure function will shut down the entire system in case of a power failure to the supply fan or the Motor Speed Controller or mechanical failure. During a following call for heat, the Operating Priority function will detect if one or more appliances can be operated safely and with proper air supply. If so, the appliance(s) will be able to operate without fan operation. After two (2) hours, fan operation is checked and if present, the control will go back to normal operation. Otherwise, it will continue to operate in Operating Priority mode. The self-check is repeated every two (2) hours infinitely. During a period without fan operation, the control is in alarm mode.

If the supply fan has been out of commission for seven (7) days, the Bearing Cycle Activation function will operate the fan at a low speed for a short time. This is automatically repeated every seven (7) days, if the fan has not been operating.

Any errors detected during operation are shown on the digital display screen.

  • Perfect combustion air supply at all firing rates
  • Direct or indirect air supply possible
  • Greater boiler efficiency at a lower operating cost
  • Smaller air intake
  • Reduced emissions
  • Improved compliance, even without large louvers
  • Aesthetics
MCASx Modulating Combustion Air System X with box fan, modulating pressure controller and fan control
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