Gas Fitter Practice Test 2025 – The All-in-One Guide to Mastering Your Certification!

The return air plenum is the correct location for all air filtration devices because it is where the system draws in air from the conditioned space to be circulated back through the heating and cooling system. This setup ensures that dust, pollen, and other particulates are captured before the air is reheated or cooled and sent back into the supply air plenum. Placing filtration devices in the return air plenum prevents contaminants from re-entering the living space, thereby maintaining better indoor air quality.

The fresh air plenum, on the other hand, is primarily responsible for handling outside air that is brought into the system, often for the purpose of ventilation rather than air conditioning. The supply air plenum delivers conditioned air to the areas of a building and does not typically contain filtration devices. The exhaust air plenum, as the name suggests, deals with air that is expelled from the building, and it does not require filtration since its purpose is to remove stale air and maintain air balance in the system.