I have an old Airco ACF-90MD on floor slab, made in Aug 1986 & still going strong, only used in cold weather due to having a heat pump, so no incentive to replace it. At 85 it may outlast me. To save money Heat Pump inverted V HEX was installed above furnace so 15 x 20 duct space up to return air header is partially filled by it. 2 (different) filters were a pain to source and install so I have put blanket filter material across return registers. I want to try to widen 15 x 20 duct and install a MERV 11 20 x 20 due to allergies.
Comments anyone?
