I recently had our HVAC guy out to clean my shop mini-split. He commented that it really needed the cleaning, and he was surprised it was still working well. And that I really ought to keep it cleaner. So I decided I would built a box to hold some filters to clean the air going into the split, so it would be happier in the future.
First step was building a frame to hold two of the filters I’m going to use. These are the filters I already use in my Rikon 62-450 air cleaner, so I generally have them on hand.
With the frame built, I measured the mini-split and the space between it and the ceiling. My goal was to put the filters sitting vertically, rather than the horizontal filters built into the mini-split, which sit at the top of the split, and catch dust even when the split isn’t running. I figure the filters will last longer if they’re only collecting dust when the split is running.
Everything looked as though it would fit, so I built two frames for the box. The one in the left had to work around the mounting system for the post for my post drill, which I needed because it was impossible to buy a straight 6x6 during the early COVID days, so I got a twisted one and figured a way to make it work.
With the side frames built, I cut panels to fit on them from a scrap of MDF I had. Then I used more scraps to connect the two side frames together and provide an opening for the filter holder.
Next up was to seal up the large gap between the mini-split and the filter box. But I couldn’t build anything rigid here, since the front of the split pivots up when it opens so you can clean the filter. My solution was to tape in a piece of ¼ inch MDF. Hopefully the tape will remain flexible enough that I don’t need to remove it, but can simply flex the piece out of the way.
With that, it was time to put the filter carrier in place. I had hoped that it would stay with no attachment, bu it wanted to tip forward, so I put a single screw in to hold the top of it in place.
And with that, everything was done except inserting the filters. With them in place, it’s done. The filters don’t seem to hurt the airflow from the split when they’re clean, but I’ll need to keep an eye on things as they get dirtier. It wouldn’t do to burn out the fan in the split.
Thanks! It’s keeping quite a bit of dust out of the split so far, from what I can tell. The real proof will be after a month of operation. Usually there’s noticeable dust collected on top of the split after a month, and I’m hoping it’ll be pretty clean up there when I check around Christmas.
I did something similar with my mini-split at my other shop after seeing how much crud built up on the fins. I used some wide weather stripping that has the adhesive on one face along the bottom of the filter box where it butted up to the mini split. Once I get a mini-split for the new shop I'll do the same thing. I'm contemplating a ceiling mounted high air flow air filter since it doesn't use the fancy and really expensive filters like the Jet filters.
One of the things I really would like with my Rikon air filter would be some way to have it run automatically, but I have to push buttons to start it. Been thinking about bypassing the control board entirely and just hardwiring it into the same circuit as the shop lighting, so any time the lights are on, that filter is running.
My HVAC guy had some stuff in a spray can for cleaning the fins that was pretty neat. Spray it on the fins, and it foams and brings all the crud out to the surface where you can wipe it off with a rag. It worked pretty well, and if this box doesn’t do the job completely, I’ll be calling him to find out where I can get that stuff.
I know this doesn’t help you directly, but that’s of the things I love about my shop automation. I use the GRIT Automation system and it’s got a specific trigger for air cleaners. The trigger has a built in particulate sensor that is customizable. When it gets tripped, the filter comes on until the particulate level falls below a preset level, then it turns off.
It’s probably not worth the money to build your own trigger with a sensor, but there are other home automation system like SmartThings or HomeKit that you might be able to use.
Ryan/// ~sigh~ I blew up another bowl. Moke told me "I made the inside bigger than the outside".
Yeah, Ryan. The main problem with the air cleaner I bought is that the only way to remote control it is via the IR remote. The control board in the Rikon is pretty limited.
Pete, I went low tech with my minisplit filter upgrade. I started to make a box like Dave did but because it is so close to the ceiling, the filter box was going to have to be on both sides of the unit. I tested the airflow using cardboard and that configuration restricted the intake even without a filter and significantly reduced airflow. By simply laying 4" filters on top and sealing around them with duct tape, the air flow only drops by between 5 and 10 percent when I measured outflow with an anemometer. I also measured amps drawn with just the fan running with and without the filter and there was no measurable increase in amps with the filter in place. When I have opened it up to inspect the internal filter (just a screen really), there is literally no dust on it and no dust that I can see on the condenser vanes either. I suspect that my my nearby DIY Corsi-Rosenthal box fan air filter does the heavy lifting as far as keeping the dust out of the air and away from the AC filter (there is very little on the filter even after more than a year) so I suppose that this is really the second line of defense. I use a motion sensor to turn on the CR air filter so it is always on when I am out there and it stays on for 20 minutes after I leave. Note that you may need to seal around the front door of the unit as well to prevent it from sucking air around the door and bypassing the filter upgrade because of the increase in resistance that the filter may cause.
I had to order custom sized filters from Filterbuy.com to get ones narrow enough for my minisplit. The cost was reasonable. They did not have an option to order ones that were long enough to completely cover the intake so I ordered two shorter ones and simply taped them together to form one longer filter. IIRC, I ordered Merv 11 filters and I highly recommend 4" filters.
EDIT to add: Another thing to consider when adding a box as Dave did is that because the front door pivots up, you have to make provisions for that so that you can inspect and clean out the inside from time to time. I was going to have to completely remove the plenum box on mine so just removing the tape on the filters is much easier.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.
I’m running MERV 13 filters in it now, and the airflow doesn’t seem to be reduced, and the screen inside the mini-split is staying clean. I ordered filters identical in size to the ones needed by my Rikon air filter that sits next to the split. That pulls a lot of dust out of the air, and mostly runs while I’m in the shop. The filters on the split last about twice as long before they’re visibly “full” as the one in the filter during the summer, but in the winter, I change all three filters at the same time, since the split runs 24/7 (set at 61F) to make sure the plumbing in the shop doesn’t freeze.
The Rikon filter calls for MERV 9 filters, but has another “inner filter” which is supposed to be equivalent to a MERV 13. I’m going to try it with a MERV 13 from FilterBuy next time they get changed and see if that makes it happy or not, because they’re enough cheaper than the Rikon filters that I don’t feel bad changing them more often.
Pete, for my first prototype of my approach and before I found that you could get custom sizes from Filter Buy, I cut a 20x20 (or was it 24x24?) 4" filter in half and taped it back together lengthwise using some cardboard to replace the sides as a proof of concept. It actually worked pretty well until I finally ordered the custom sized ones. I think that the filter I used for that was just one you can find at HD or Lowes, though it was probably just a MERV 8 filter. I was hesitant to put a MERV 13 filter over the minisplit intake for fear that it might create more resistance than the unit's fan can handle. Since it basically just uses a screen as a filter, my thinking is that it could strain the motor and/or lower the cooling and heating efficiency of the unit. Even big standard AC units can be restricted if you go all the way up to MERV 13 filters if they aren't designed for them.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.
