Is it worth upgrading from a window unit to a mini split in your shop? Yes, absolutely, and I’m going to tell you why.

For three years I cooled my 30×50 shop with a 10,000 BTU window unit I got for $100 on Facebook Marketplace (here’s how that went). It got the job done, but it had nothing to spare. Now there’s a Senville Aura 24,000 BTU mini split on the wall, and I should have done it three years ago.

It’s so quiet

First off, I recorded the whole video with the mini split running. With the window unit I had to shut it off to film. That’s proof enough right there.

It’s so quiet in the shop now that I can hear my own thoughts, and that’s a little scary. Working at my desk I found out one of my surge protectors, the kind with USB ports on it, makes a whining noise. I had to go unplug some stuff from it so it would quit. That’s how quiet it is. Standing 15 feet from the mini split I can barely hear it.

How it’s been doing

It was 90° outside yesterday and the shop was cool. Overnight it dropped to about 50°, and since I have it on auto it switched over to heat. I walked in this morning and the shop was still 75°. It’s basically perfect all the time.

The air in here has been nice and dry too. We’ve had a couple 90° days so far. I haven’t been through a winter with it yet, but so far it’s been fantastic.

Pulling in a hot truck

My truck needs a water pump, which is why it’s sitting in the shop in the video. I pulled it in hot and the mini split recovered pretty quick. It ramps up a little, from a slight wind noise to a little more wind noise, and that’s about it.

When I pulled a hot car in with the 10,000 BTU window unit, it would run until 2 in the morning before it finally caught up and shut off.

Sizing it right

This is a 24,000 BTU unit. I could have gone with a 36,000, but bigger isn’t better. Too small and it runs forever. Too big and it cools the shop down and shuts off before it pulls all the humidity out of the air, so you end up cold and clammy.

So size it to your space, your insulation and whatever you actually do in that shop. I think I got pretty close.

I went full nerd on this and built a calculator. The square footage and insulation part is everywhere online, you can find that with a Google search. What I added is how many times you open the big door, how many hot cars you pull in during a workday and how long your workday is. I rarely open my big door, and it’s still almost a quarter of my summer load. For my shop it came out to about 24,600 BTU of cooling, so the 24k was the right size. It’s called the Shop A/C & Heat Calculator.

Why I went with the Aura

This is Senville’s Aura model. It has a couple extra features, like Alexa. I have to say that quietly because she’ll pick up.

The bigger deal is heat. Mitsubishi calls it hyper heat. The Aura can heat down to about -20° (Senville says -22°F), and in Senville’s lineup that’s the reason to get the Aura over the Leto. If you live somewhere cold, read up on the heating ratings before you buy.

I’m still keeping my electric heaters. There’s the 2,000 watt doorway heater I’ve talked about before, and the 5,000 watt heater on the wall, which is brain numbingly loud. The mini split should be able to handle pretty much everything on its own though.

When I turn it off

The only time I shut the mini split off is when I’m fabricating. Grinding, welding, painting, anything that puts junk in the air. I turn off the mini split and run either the exhaust fan (it’s behind the lift, so you can’t see it in the video) or the shop air filter. That way I’m not sucking a bunch of junk into the evaporator coil and clogging up my brand new mini split.

If you only work out there on weekends

This one I didn’t fully figure out until I had my own shop. If you keep the shop at a reasonable temperature all the time, your slab stays at that temperature too.

Say you only get out there on weekends. It’s winter, the slab is basically frozen, and Saturday morning you fire up the big heater. The air warms up, but the second you lay down on that concrete it’s freezing. It probably takes a couple days just to warm up the slab. The cold comes up through your shoes, your feet get cold, and you don’t want to be out there.

So keep it at a reasonable temp all week. I think the lowest this mini split goes is 60°F. Leave it there. It might cost you a couple more dollars during the week, but going from 60 to 70 on a Saturday morning is no big deal for a properly sized unit. The whole point is to use your shop for whatever you wanted it for and be comfortable doing it.

Same goes if you’re thinking about a heated slab. I plumbed mine for radiant heat and never hooked it up, because keeping the shop warm keeps the slab warm.

The window unit is coming out

I gave them about a two week overlap because I have trust issues. The mini split is working fine, so the window unit is coming out.

I did this the hard way because I’m a cheap ass. Probably shouldn’t have, but I learned a lot and the window unit worked fine. Now I’ve got the big boy air conditioner.

If you’ve got questions, ask them in the comments. I’m happy to help out.

Stuff mentioned in this post

• Senville Aura 24,000 BTU mini split
• 5,000 watt wall heater (if you buy one, find a dumb one with a knob instead of a digital screen, so it stays on after a power outage)
• 2,000 watt 240V doorway heater
• Shop air filter
• Exhaust fan
• Shop A/C & Heat Calculator (the spreadsheet I built)

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