I want to install a mini split in my shop before it gets hot, and to stabilize humidity levels. The shop is approximately 30’ x 50’ with 18’ ceiling. I’m thinking a 3 ton / 36,000 BTU with 2 zones - one over the shop floor and the other in the loft at the opposite end. 20+ SEER rating is preferable. I have plenty of 220 capacity, and can bore a hole through the rear wall and run piping to a fenced cage behind the building.
Does the unit capacity sound about right for my shop size?
Any brand recommendations?
I’m confident I can install a pre-charged DIY kit but any recommendations for a contractor are appreciated.
Most mini splits are very DIY capable. You’ll need a vacuum pump with the correct adapters. I have one you can use. As far as sizing goew, I’m not sure on that.
Insulation (or lack thereof) drastically influences the BTU/hr needed. Also how much outside air intrusion? This brings in heat just like through the walls, sure, but if it’s actually bringing in outside air that also includes moisture. That moisture has to be condensed out to cool the air, and condensing moisture consumes a surprisingly high amount of the BTUs.
It sounds like a big shop, but 36KBTU is about as big as you’re going to get anyways. So you needn’t wonder if this one is too small. Is it too big? That question’s on the table, but no one can guess without a fuller picture of the wall and ceiling composition. Even then, it’s a guess. But, a rule-of-thumb is 20BTU per sq ft= 30KBTU. Plus you’ve got high ceilings, need mor BTU. So I think you’ll need 36KBTU.
Usage pattern matters too. If you plan to let this run every day from dawn to stay cool, that can live with a smaller unit than, say, planning to leave this building off, un-air-conditioned until you walk in at 3PM and turn it on and want it cooled down in like 45 min. That’s less energy than leaving it running all day, but you need a larger unit to achieve that performance.
The shop is fairly well insulated as far as light industrial buildings go. It’s a middle unit. Insulated roof and roll up door. I’ve patched any potential leaks. No windows.
I used the 20x multiplier and added a bit for the high ceilings to get to 36kbtu
I’m there full days 6 days a week so I plan on trying to keep a fairly constant temp while I’m there and then turn down / off in the evenings and on my off days. It looks like the better units have remote control and variable speed to minimize cycling on/off.
I am 99% sure this was the model I went with. I got it off an auction site for a pretty good deal. So I really didn’t research the company that much. All that being said I am very happy with it.
For my shop, I installed a 27K 3-Zone Mr. Cool DIY Mini split compressor, a 12K and a 9K indoor unit respectively for the garage and small workshop.
The install was a SNAP with two people, a ladder, a step-stool, common hand tools, a drill, and a laser level and a little forethought in planning before ordering the unit. Mr. Cool has an excellent reputation, have Smart House ( Their Mr. Cool App, Alexa, and Google Home ) integration via Wifi units that go in the indoor units, and a good range of accessories.
They also have an excellent calculator on the website to calculate your needs. I ordered my units from Ingram Air/Cooling and all the pieces I needed ( including the 220V electrical wiring ) came out to ~$2400. I was very lucky to have help from a professional electrician that I met during my time with ATX Hackerspace… he helped me wire up the 30A 220V circuit, and was a great second pair of hands to get the cooling lines installed and covered, as well as hang the outdoor unit.
The best part? The cooling lines JUST BOLT TOGETHER! No flaring tool, no vacuum pump, no messing with freon… it’s all in the pre-charged lines.
I have a 25’ x 25’ shop with 15’ ceiling and loft area, with a small 180 sq ft backroom. I have a Daikin that is 1 ton / 12,000 BTU. I print so I need to keep humidity down for paper. It works like a dream. I don’t keep it really cool or super hot. So perhaps you only need two.
I like my Daikin but I have heard that Mitsubishi is really good.
