Struggling to cut garage/work space odors, unknown allergen, with pets and an old gas furnace (29 years). I've added filters on both return and furnace to tackle the issue, although I know one or the other is better on system. Concerns about a cracked heat exchanger drawing in air from the garage persist despite sealing with metal tape. Awaiting IRA incentives for a gas to electric heat pump conversion due to HVAC issues and reduced air flow measured at 0.64 static pressure during recent system evaluation. Cost is $18-20k to be qualified before rebate/credit thus the wait.

Just having the return filter doesn’t reduce the odor/allergens. I used to run just the return filter (no furnace filter) until allergies got worse about 5 years ago and garage smells increased with projects. So looking for input until I get a new system put in.

On furnace FPR 7= ~Merv 11 On air return carbon odor removal filter merv 11