FAQs

Direct Gas - Fired

  1. To safely dilute products of combustion, what cfm of outdoor air is required for each 1,000 BTU/hr (direct gas fired equipment)? How should an air curtain be operated in order to satisfy the above requirement?

    Based on 100% indoor air, 4 cfm per 1000 BTU/hour is required. The air curtain should be operated with the door open to entrain outside air with the air stream. This will provide approximately 25%-30% of CFM of outside air included in the air stream to dilute products of combustion from the direct gas-fired heater.

  2. Why is a hand/off/automatic switch not recommended on direct gas systems that use 100% indoor air?

    The air curtain fans should not be operated with the door in a closed position. NFGC specifies a minimum of 4 cfm of outside air per 1000 BTU's (provided from the heater) to dilute the products of combustion produced from the heaters.

  3. What is the standard gas inlet pressure(s) for all direct gas fired systems?

    1 - 5 pounds range.

  4. Why are the direct gas fired heaters cabinets 48" deep?

    To provide even heat distribution. Air mixes more evenly with the burner flames and also the length is needed to control the flame.

  5. What are the three most common type of gas trains for most direct gas fired appliances?

    FM (Factory Mutual), IRI (Industrial Risk Insurance) - most expensive, and ANSI (American National Standards Institute) - least expensive.

  6. What can be done with all belt driven, direct gas fired systems, top air inlet, if there is insufficient room for the motor(s) to be mounted out in front of the air curtain?

    Extend the length of the cabinet on the side to provide a base for the external motor base. The additional cabinet area will be empty with the outlet nozzle extending over the door opening only. The motor should be mounted out of the air stream due to a 100ƒF temperature rise.