CAN1-3.7-77 (R1996)

Preface

Air starvation in industrial buildings is a growing problem with the many process operations requiring a high rate of air exhaust. This situation may become critical in cold weather, when all the doors and windows are closed creating a negative pressure within the building.

Scope

1.1.1 These requirements apply to direct gas-fired non-recirculating make-up air heaters intended for use with natural, propane, and propane-air gases.

1.1.2 These requirements apply to complete direct gas-fired non-recirculating make-up air heaters used to heat outside air to replace mechanically exhausted inside air where all of the heat and the products of combustion, generated by the gas-burning device, are released into the stream. These units are also referred to as direct gas-fired 100% make-up air heaters.

1.1.3 These requirements apply to direct gas-fired non-recirculating make-up air heaters provided with automatic control devices and interlocks and designed for operation with fully modulating gas flow control, with either manual or semi-automatic start-up.

1.1.4 These requirements apply to direct gas-fired non-recirculating make-up air heaters designed and applied solely for replacing exhausted inside air with heated outside air.

1.1.5 These requirements apply to direct gas-fired non-recirculating make-up air heaters with maximum rated inputs not exceeding 10,000,000 Btuh. Heaters having maximum rated inputs greater than 10,000,000 Btuh which incorporate additional safety features may be investigated to the intent of these specifications.

1.1.6 A make-up air heater which complies with these requirements shall not be considered acceptable if it has features which impair the results contemplated by these requirements.

1.1.7 The gas burner and combustion system shall be of the modulating type. The minimum rate shall be no greater than that calculated by the following relationship:

Minimum Btuh = 6.0 Maximum Btuh/Design Temperature rise

The turndown range need not exceed 20:1.