Traditional Ducted Heat Pump in Dedicated Workshop

[Jason Fields]

To reduce the air resistance, when you build your filter boxes make them several times larger that the vent opening and make them with a standard size filter. My filters are 12 x 12 x 1 and I get them from Filtersnow.com.

Thanks Lee, I'll check out filtersnow.com

I use 20x20 filters on the air intake to my furnace, a metal frame with grill made for the purpose. Just wish I had built a box a foot or so high to set the furnace on, so the filter would be up higher on the wall, instead of floor level. Would significantly increase life of the filters.

Thanks for the info Jim. The filter on mine is going to be about 8 inches above floor level.

Jason, everyone has been providing good info so far. Regarding filter brand I wouldn't get hung up on a particular brand. It's not that critical for what we are doing. Merv rating above an 11 without adequate filter area may cause airflow issues with your system. Do you know if the air handler has an ECM motor or not? This can be an issue with a PSC motor.

The reason for running prefilters is you will save having to replace the expensive main filter frequently.

I spend on average 20 - 30 hours a week in the shop.

The info has been great and has given me a solution that I can implement with very little work and cost.

Mine has a variable speed motor. There is a louvered vent in the wall of the closet that houses my air handler. The air handler itself sits atop a metal box that is about 24 inches in height, and on two sides of the metal box there are smaller louvered vents. At the bottom of the air handler itself, just above where it sits on the metal box, there is a 20 x 20 x 1 filter that is inserted into the air handler horizontally. Based on what's been said here, and the great info I've received, my plan now is to use the louver covered opening in the closet wall to house a 16 x 25 x 4 inch filter stacked with a cheap 16 x 25 x 1 pre-filter directly in front of it to catch the bigger stuff.