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Thread: DIY Filter Box for Mini Split?

  1. #1
    Join Date
    Oct 2008
    Location
    New Jersey, USA
    Posts
    41

    DIY Filter Box for Mini Split?

    I decided to go with a mini-split heat/AC for my new woodshop (see the cinderblock barn to woodshop thread elsewhere on this forum). One of the concerns I have is dust getting into the wall unit. I recall seeing somewhere on the web (could have been Sawmill Creek, or maybe some other ww forum) where some folks have made a plywood box that holds filters and fits over the interior wall unit. Has anyone here done something like that? Any advice to offer? Types of filters used? How well has it performed?

    Thanks!

  2. #2
    Join Date
    Nov 2007
    Location
    Hot Springs, VA
    Posts
    763
    I have mini-split unit in my shop for last 5-6 years. First three years I cleaned and vacuuming inside plastic filters religiously every 3-4 month. Now every half years or after very messy sanding. Never have any problem with AC/heat pump mini-split. Plus I would not recommend to put anything to restrict airflow to/from inside unit.
    Ed.

  3. #3
    Karl,
    I built a pre-filter box that fits over my wall unit. It's quite simply built from 1/4" ply, glued and tacked to a stick frame. It slides over the top of the unit, held to the wall with a french cleat. I use a cheap fiberglass filter that slides in a channel from the front of the unit. It's compression fit to the unit with foam weather stripping so there are no air gaps and all the air to the unit is drawn thru the fiberglass filter. The lower fins of the wall unit are not covered by the pre-filter box, just the air intake vent on top.
    My dust collection in my shop is lacking and I found a lot of dust collecting in the unit, even if I cleaned it regularly (monthly). The pre-filter definitely catches a majority of the dust that found it's way into the heat pump before I installed it. I wouldn't use more than the blue fiberglass filter as a pre-filter. It allows sufficient air flow into the unit. Better filters will definitely restrict air flow. I don't have any pics, but if I get a chance, I'll post some.

  4. #4
    I don't have a mini split, but used a 20x20 metal filter frame with door to filter the air to my furnace. Mounts on the wall. You should be able to buy one at any furnace sheet metal supply store. I use the corrugated filters, the fiberglas only stops large pieces, not dust from entering your unit.

  5. #5
    I have a mini split and I just vac and/or wash the filter regularly. I also run an air cleaner from the ceiling that runs anytime that I am working in the shop. If I make lots of dust, I will shut down the mini split for a while until the heavy dust is collected. The mini split heats/cools the shop fantastically. Love it.

    Red
    RED

  6. #6
    Join Date
    Oct 2008
    Location
    New Jersey, USA
    Posts
    41
    Thanks to all who have responded. I greatly appreciate the advice.

    The salesman I'm dealing with reached out to Fujitsu to ask them about filtering. They didn't have any advice to offer other than to be sure whatever filter is used does not restrict the airflow too much.

    I will let you know how it turns out.

  7. #7
    Karl, how did this turn out?

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