New answers tagged air-filter
It sounds to me like the 'return vents' are actually exhaust vents from the heater. My attic heater has a return duct directly below the heater at floor level in the living room. The filter is in front of this return duct (20" X 30" filter). There should be a rather large flange on the bottom or side of your heater for the return duct to attach. It ...
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