When it comes to make up air units, there are a couple of different types. Direct fired, like in the video, and indirect fired. HVAC technicians should be aware of the difference. Direct fired make up air units have the burner mounted in the air stream, the products of combustion are dumped into the space. DF units must be mechanically interlocked with an exhaust fan(s) and are commonly used in kitchens and warehouse applications. Indirect fired make up air units use a burner assembly that includes a heat exchanger, a common application for this type of unit is in multi story buildings for pressurizing hallways. Happy HVACing

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