30×40 Shop Part 8: Mini Split Air Filter Update

Video Notes:

– Build video and article for the filters: https://jayscustomcreations.com/2019/10/mini-split-filters/
– The filters are working as intended. I have no way of measuring any performance change but the units are maintaining a comfortable temperature in the shop during all seasons. The units remain quiet and the fans never reach full speed even on the hottest days of the summer.
– These are the 20x20x1 MERV 13 filters I use: https://amzn.to/32rUDzI
– I designed the filter boxes to take the same size filters as my air cleaner cart. When I designed the air cleaner cart I made it fit the same size filters as my previous house HVAC system. Make things the same size and you are more likely to keep extras on hand, as they fit everything.
– I recommend making an air cleaner cart as I did. They are inexpensive and very effective. Contact local HVAC contractors to see if you can get a used blower motor for cheap or even free. For more info on the air cleaner cart: https://jayscustomcreations.com/2016/05/mobile-air-cleaner-cart/
– This is what I use to monitor the air quality: https://amzn.to/2QpLZwg


  1. Jay-thanks for this and all the other articles and videos you do. You do an awesome job and service! I have just completed my long planned shop of 18×38 (the largest the county would let me build that was not attached to house). I plan to try to do a bigger shop attached to house when I can figure out how as I have trouble getting engineer to do drawings to connect an inexpesnsive steel building even when I get the steel building engineering to agree to do the design at ‘risk level 2’ habitation which seems to be required. I will get my full size shop some day and for now will share my car/boat work with my woodworking in this large garage.

    I want to put in an ac when I return to FL in the fall and I had watched your first video on this. I am glad to get this update on how it’s working out. Thank you for doing the update!

    Keep up the great work-hopefully our paths cross some day in person, once COVID craziness is under control (which hopefully is some day).

  2. Jay,
    try to weight them before installation and then when you cycle them into the air cleaner cart and the ones that come out o f the cart as well. this will tell you about how much is being filtered at each step. If your busy in the shop with one particular type of job it might give you an idea of what puts the most debris into the air.

    it appears that the C&C puts off alot of micro particulates that the unit above it catches.

    Thanks and keep up the great work,

    • I don’t think the CNC is making those filters any more dirty than normal. The dust collection at the CNC is really good. The reason why those stay dirtier is that I use that mini-split head the most as it is blowing on my office computer area. Sometimes I just run it by itself.

  3. Pretty cool, whenever I get around to building a big shop, this will be something I’m doing for the mini-splits.

    As far as the filters, is there an easy way to build some adjustments into the box? I was almost thinking have the box that is connected to the wall solid, then have some face frame system that is adjustable to take up the slight differences in filter sizes. Hopefully that makes sense coming through text.

    Anyway, now I have to find out a way to do something similar for my window unit in my small temporary shop.

    • As long as I can get the filters in the opening and there aren’t any signs of dust leaks or dust trails between them then I don’t think I’ll be modifying the box any time soon.

  4. Jay
    I’m sorry you made the same mistake I did about the size of the filters. How did you decide how many filters to put on each AC?

    I also made a air cleaner using the fan from an AC but eventually took it apart, it made too much noise. How noisy is yours? I ended up using box fans with 20×20 attached to the intake, they are quiet enough that I just leave them running all the time.


    • I went with as many filters as I could reasonably fit in the space. I’d put more on each if I could. It’s one of those things that can’t really be overdone. The more filters you have the less time you will have to spend on maintenance and the longer they can go without needing to be replaced. Each 20×20 filter has a tremendous amount of surface area. They are pleated so it’s much more than just the size of the filter. The more the better!

      My air filter cart is about as loud as my house furnace blower. I can hear it but it’s not crazy loud.

  5. My mini splits open in the front so one can remove the inner filter you were showing us. I do that ever so often to vacuum them. Is that the same with your units? I have Mitsubishi.

  6. Jay technically you could make a frame over the opening in the mini spit opening and just filter there. It would not have any effect on the unit at all. or minimal. The fact that you have made that big of a box overhead and provided the units that much breathing space would not give those units any choke point at all. If anything those boxes would make them perform better because of the free flow of air above them Great job.

  7. Great video Jay. The topic of air filters or air filtration is not very popular in the woodworking community. I believe you have put more emphasis on this topic than most. With the air monitor, dust collection, pre-filters, etc. it’s a nice collection of information.
    The dust cart filter is on my list!

    Patrick Melchior

  8. Hey Jay thanks for the update, the timing is impeccable because I am planning to do the same thing. I am using 16×25 filters because the head unit is tighter to my ceiling. I cleaned my head unit last week omg I should have sent you pics it was terrible after 12 months. I also have the cart you made and it has made a huge difference in my shop. Thanks again! Now I’m hungry for ribs.

  9. unrelated note — did you switch to using a mic with the rode wireless go for aesthetics/comfort (not having the transmitter clipped to your shirt collar) or for performance?

    I’m trying to buy a set but they are backordered on all the major places…

    • Performance. If cliping it on the inside of the shirt is a perfect score of 10 for comfort and convenience then using a mic and clipping it to my hat is a 9.9. Super close but the shirt was a touch more convenient. The problem was it flipped inside the shirt a few times while working and I couldn’t feel the difference. The mic was muted against my skin and I lost a bunch of audio clips because of it. It is consistently perfect audio in the hat but a tiny amount less convenient. I just dedicated a hat for the mic in the shop and take the entire hat to the charger when needed.

  10. I just build my version of yours, but used (4)(2 on top and 2 on the front)12*24*4″ thick, with a 1″ pre-filter. I still need to build my connector band and seal it up! Thanks for the inspiration!
    I have a pic on my Instagram, tonyozimek.

  11. Thanks for the update. I have a minisplit in my shop and plan to upgrade to adding a filter box to it. Your shop filter box is also, something that might work in my shop but will integrate into the table saw extension wing. And, yes, I could smell those ribs… in my mind. ????

  12. I have the same mini split and it’s great but what I don’t like is that the fans run all the time even when the unit is not calling for cool. Does your do that?
    Good vid,

  13. Jay – love your videos! As for the filter box make an extension on both ends and close off the face frame. Let the filter on each end slide past your current end opening thus allowing some flexibility. Just a thought – that way if size changes in the future you have it covered.

  14. Watched your blog on safety the other day and didn’t get a chance to comment so i adding it here:
    Finger rings i have worked in industry for many years an have seen some bad things happen -one example a person jumping off a truck and his ring gets caught his ring and finger stays on the truck he hit the ground.

  15. I find these videos so valuable. It’s these type of details that help all of us regardless of skill level.

    I would like to make one of those Dust Carts (and put my DeWalt planner on it like you did back in the day) but I’m having a hard time finding a blower motor. Did you pick yours up off CL / Facebook Market Place / etc? What did you search for? I’m in the Boston metro area, I feel like it shouldn’t be so difficult to find one.

  16. Thanks Jay for the update and the great idea. I just installed my unit in June and finally installed a similar filter on mine yesterday. It’s working well.

    My mini split head unit sits between two old kitchen cabinets, mounted to a spaced 2×12. I left about 3” on either side of the unit and lowered it to where the unit sits flush with the bottom of the cabinets when the blower is off. There is 5” behind the intake vent and the cabinets sit 5” from the actual ceiling. This left me 19” to the top of the cabinets. I built a 40”x19” cabinet and use 36”x18” filters from amazon. There only Merv 8, but I figure I’ll replace them more often, or upgrade after this dozen filters if I don’t like the performance of these.

    Obviously, none of this is my idea, and purely inspired by your genius! Thanks Man! I know this will save my unit!

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