Can you cool a 30×50 shop with nothing but a 10,000 BTU window unit? The answer is it depends. It depends on where you live, what you’re doing in your shop, how often you open the door, and what kind of insulation you have.
My shop is a 30×48 pole barn (build series here) and I’ve been cooling it with one cheap window unit for about three years. Here’s how it’s built and what I’ve learned running it this way.
How my shop is insulated
It’s a pole barn with 6×6 posts. I framed out the inside with 2x4s, put in R19 insulation, and hung 5/8″ fire rated drywall on the walls.
The ceiling is 13 feet. Up there it’s a vapor barrier, then ag panels, and then I blew in R60 of fiberglass on top. I think that’s around 18 inches, but it’s been a long time since I looked it up. I went way overkill. I did it myself so I was able to use more, and I went through a lot of bags. It’s very thick and it’s been working very well.
Under the slab there’s 2″ XPS foam board because I set the floor up for hydronic heat. It’s all plumbed. I never bought a boiler and never even turned it on. (Here’s the parts list if you’re curious.) The foam is still down there doing its job though.
So there’s insulation under the slab and all throughout the shop. That’s the whole reason a unit this small can keep up at all.
The window unit
It’s a 10,000 BTU window unit mounted about 10 feet up the wall. I paid 100 bucks for it on Facebook Marketplace and it’s been cranking for about three years now.
For reference, the shop is 1,440 square feet with a 13 foot ceiling. Most AC sizing charts put a space that size somewhere around 30,000 BTU. I knew going in this wasn’t optimal. For a hundred bucks I really wasn’t that worried about it.
I’m in the Midwest, so summers are hot and humid. With the insulation I have, this thing holds the shop fine. When I shot the video I was actually kind of cold. It was a little cooler outside that day, but still.
Where it falls apart
This unit has enough capacity to keep the shop stable. It doesn’t have any spare.
As soon as I open my 18×12 door and bring in a hot car, it’s done. Every car you pull in is a whole extra load of thermal mass that has to cool down, and a 10,000 BTU unit has nothing left to give. It’ll run until 2 o’clock in the morning before it catches up.
If you’re pulling cars in and out all day, this is not going to cut it. Honestly the new unit I bought might not cut it either. You’d need something bigger.
Pre-cool before you need it
Whenever you’re running something undersized, get ahead of it. If I know people are coming over, or I know I’m going to open the door to bring a hot car in, I turn it down a couple degrees ahead of time. That gets everything in the shop colder so it has a head start and can keep up.
Noise
Standing right next to it, the window unit puts out about 62 to 65 dB.
What about heat?
Same question, but for winter. I’ve got a 5,000 watt heater up on the wall (more on that setup here).
Does it work? Yes. Does it heat the shop? Yes. Is it loud? Yes. It’s even louder than the window unit. That heater is obnoxious.
A year or two ago I added a 2,000 watt 240V heater in the entryway. It does a good job balancing things out between the big heater turning on and off, so the big one doesn’t have to kick on as often. It helps, but it’s still not a solution.
So can you run a shop off this setup?
Absolutely. I’m out there every day for most of my day. I probably spend as much time in the shop as I do in the house, maybe more.
Does it work? Yeah. Is it mildly annoying? Also yes. Am I ready to upgrade? Definitely.
If your shop is insulated this well and you’re not opening the big door all day, a cheap window unit will get you by. If you’re in and out with vehicles all day or your insulation is thin, plan on something bigger.
What’s next
I picked up a Senville 24,000 BTU mini split. It’s sitting just out of camera shot and I haven’t even taken it off the pallet yet. I wanted to answer this question first, after three years of actually running off the window unit.
The install is next, so stay tuned for that one.
If you have any questions, ask them in the comments. I’m happy to help out.
Stuff mentioned in this post
As an Amazon Associate I earn from qualifying purchases.
Got a project in mind?
If you're tired of getting ignored by big shops or just want someone who actually gives a damn about the build, that's what I do.
Let's talk →