Direct gas-fired air-handling units (AHUs) have provided efficient, reliable makeup air for many high-exhaust/infiltration industrial applications and facilities, such as paint booths, distribution centers, warehouses, and factories. Concurrently, direct gas-fired AHUs have seen limited utilization in commercial applications, with commercial-kitchen makeup AHUs being the most prevalent application. With ever-increasing energy costs, it is time to take another look at direct gas-fired makeup AHUs for commercial applications.

This article will describe the differences between direct and indirect gas-fired AHUs, provide component descriptions for a typical direct gas-fired AHU, highlight applicable codes/standards and any commercial-application limitations, note the advantages and disadvantages of direct gas-fired AHUs, and provide a number of potential commercial direct gas-fired AHU applications.