Sizing your shop for a mini split
How many of you are using mini split to heat and cool your shop? I’m building a 24×40 pole building with spray foam insulation. I’m curious what size units you are using and the temperature ranges you are trying to hold. I live in southern Michigan just to give an idea of climate. Thanks!
Can't help you with that cold a$$ climate but something to factor in is dust control. If vented back into the room there is some heat gain from the motor. If vented out you can quickly exhaust all of your conditioned air. Only solution I have found is going hand tool. In my South Carolina zone I can make electric heat and a window unit work but I am only 10' x 16'
I put one in last year and I'm loving it. Small interior room w/o windows, so a vast improvement in summer. The inside half is up in the ceiling so no wall space was lost. Winter was never an issue with the furnace in the next room. 2-zone 24000 btu unit, the second zone is in my office. I keep the office about 70. If I go that low in the shop everything metal is too cold to use comfortably so more like 80+ with the dehumidification making the real improvement there.
I don't use it in the basement shop. But I have a 2 zone 24,000 unit heating and cooling an 800 sf addition and 350 sf upstairs bedroom, and an 18,000 unit heating and cooling the 800 sf downstairs.
I used 2/3 less oil this year than the year before I installed them. Hot water is still from oil. And since oil jumped from 3.79 gal in February to 6.15 gal today, I'm really really glad I did.
I can't answer as to dust in the shop, since I don't have one there.
i have similar sized shop, 24x35, 22 ft ceilings, spray foam in ceiling, bats in walls. i installed a 24k btu mini split (mitsubishi msz-gl24na) and couldnt be happier. heats or cools space 10 degrees in less than an hour, quiet and cheap to run. you will need to blow out filters every 6 months, but its easy and quick to do. with electricity costs in my area (seattle) i think it costs about 70 CENTS (!) per hour to run.
I have an insulated 450 sq ft shop and installed a Mr Cool mini-split. 18,000 unit, I think. It keeps my shop cool in the central Tx heat and humidity. Second benefit is that brand is completely DIY - no AC technician has to show up. I spent less than $2,200 on the unit and electrical. Comparable unit from an AC company would have been at least $2,400 more. My dust collection does not vent outside, so I installed extra filters around the evaporator intake. I'm very pleased. Regarding sizing, I called the company that sold it to me, Air Marketing Group, and got excellent help on which unit would best fit my shop. I think my unit is rated to 750 sq ft, but I wanted to be over rather than under in capacity.
Good to hear. I have a 400sqft garage and I have been eyeballing these. I'm tired of tap dancing around the fact I have an open flame in tje winter and my BIG window AC unit died. Thanks!
Always get them installed professionally. The small extra cost is worth it both for the time taken and the better evacuation of the system and/or exactly sized piping, which improves efficiency. Properly installed you get 4 or more units of heating for every unit of power used. The installer will also tell you the best placement of the units and will ensure they are sized correctly for your purpose. Larger units also need beefy wiring to be safe in operation.
Looking at the climate chart for where you are, there are devices that work that cold with air source units. Mitsubishi promise full heat capacity down to -15c or 5F though likely they will not be so efficient at that temperature gradient. If you can afford it or have the space, then a ground source heat pump is an excellent option in more extreme climates.
I have a similar sized room in a warmer climate ( -4c to +28c) that was assessed as needing 6KW of heating and indeed, that is about right so I'm GUESSING that you will need at least 7.5 or even 10Kw of heating for comfort.
That having been said, if you are not in the shop all the time then you may need a bigger unit still to warm it up. In 'Freedom Units' you probably need IRO 30,000 BTU. Don't quote me on that (Not a heating engineer!) but it should give you a starting point for costing.
Bottom line is don't DIY - sure you can, but what little you save in installation costs, you pay in your time and may lose down the line as the units are usually less efficient. Buy a really good brand as even small differences in efficiency add up over time. The difference in efficiency (up to 25%) between the best and cheapest units can be large enough to pay the purchase price and installation costs, plus you have a unit more likely to last longer.
To me $2200 is real savings and doesn't fit in the "what little you save" category.
As far as performing the calculations, there are some great resources on the internet.
I installed a Mr. Cool last summer. 18K BTU system in a 500 sq ft, 2 car garage with 16 foot ceilings. It's been great. Total cost for me was around $1800 (got it through COSTCO). It's rated at 22 SEER. As far as maximum efficiency, I do not run the system unless I am staying in the shop during the spring/summer/fall. I am very happy with the results.
I seriously considered professional installation, until I got the quotes back from the local installers in Northern Virginia. Most estimates quoted me up to $6,000, and that's after I already had a 125A sub-panel installed in my garage with an open 20amp dual-pole breaker. If I lived somewhere else where professional work would be reasonable, I would have considered it. $4000 for less than a day's work seems like highway robbery to me. I am sure the installers would have gotten the HVAC unit and accessories cheaper than I was able to source them, as well.
The estimates were worthwhile, though for confirming that 18K BTU was the proper capacity for the system.
Wow - shocked at your prices.
I've just had FOUR 4.5KW (15500 BTU) Mitsubishi units installed at work for NZD 9600.
That's about USD 6100. For FOUR top quality smaller units.
It does indeed seem that your installers are extracting the urine right now. Usual price for 'back to back' install where the outside unit is pretty much next to the indoor unit is NZD700 per unit, including delivery and all clearup.
You do have to factor in that you have a warranty with professional installation and of course, their insurance will not be cheap but even so, I think this is one area where the USA needs to get a bit of good old fashioned American competition going!
The issue is about repeat customers and maintenance with mini split units. Most AC guys hate them unless it means not having to crawl around in an attic for ductwork. They have a fixed charge volume (weight) where central units run off a ton of voodoo with the subcool and superheat tuning. That is where the dishonest AC guys make their money primarily.
Most anyone can get an EPA 608 cert pretty easily and with at least LG have the accompanying warranty support with it.
I have a 26x48 w/20' vault ceilings. I installed a DYI radiant heat in the concrete floor and a Mr Cool 24k btu at one end, and little over sized but worth the extra up size cost. The increase in my nat. gas for the radiant and the ele. for the split was maybe 5%, if that. Insulation is of course key so the foam is a great way to go. I live in central Indiana so our weather is similar. I can get the shop cold in the summer so you should be able to do the same. I don't heat with the split in the winter as the radiant is fantastic but in the fall and early spring it's not as efficient with the bigger temp swings so I use the split to "spot" heat or cool until the temps even out. As for the dust, cleaning was getting to be a pain so I built a filter box over the intake of the split and used the filters from my house furnace; 20x20x5; and that worked great. I only need to change about once a year and the units filter and coils are always clean. The install of the Mr Cool was very easy, only needed help lifting the inside unit up on to the brackets. I would install the radiant and mini without a second thought, it has exceed my best expectations.
I live in a climate that gets hot during the summer (most days in the 90s) and often at or above 100 (sometimes to 110). I wanted to be able to maintain 75 F inside the shop as I grew up on the coast and dislike hot temps. I am working out of a 3 car garage (600 square feet) with high ceilings that gets sun exposure all afternoon. After lots of back and forth convesations with the company doing the install work, we ended up going with two 18,000 BTU units. If anything it is too much (mostly a money thing) and I could have likely gotten away with a single 18,000 unit. In the four years prior to that i had tried a portable 12,000 BTU system and that didn't help at all so that's why we "over engineered" this system.
I rehabbed an older pole-barn built shop last summer that is roughly that dimension (mine is 38' x 27') in Eastern Pennsylvania, where we often have hot humid weather through July/August and pretty cold spells in the teens/20s during January/February. The shop was built in 1985, but from 2006 until 2021 it was neglected and used as a garden shed--I knew at inspection that the shop HVAC was shot. And the insulation just fair. The building is divided by a support wall under the roof peak that splits the building sort of 1/3 and 2/3 (now bench room/office and machine room). The legacy HVAC consisted of 2, independent, 35-year-old heat pumps--one on each side of the wall.
The first HVAC contractor came in and starting talking about replacing both air-handlers and condensors. I reminded him I wasn't going to live in it and asked about using mini-splits...a solution I had used my previous last (100 year old) house... either two single head units or perhaps a multi-head unit. The price was stupid high like $18K!! installer felt with the high ceilings and large machine room it the volume would require a large unit. And the dust would require a specialized filter unit.
I called a second HVAC contractor to see about alternate opinions. He concurred that the Mini-split systems wouldn't easily handle the volume of air in my high-ceilinged machine room without perhaps two heads...and the line-sets to run between the outside unit and inside heads is a big part of the expense. But, he didn't think two independent systems (like the original) was necessary either. Instead, he recommended a single 3 ton 14 seer heat pump system...and tied the two existing duct lines together with flexible insulated tubes over the dividing wall. The new air handler, outdoor condenser, duct mods and install were about $10K less than the first guys quote for mini-splits. As I was concerned about wood dust they added a 4"x 24"x 24" filter unit on the intake. Not only was I happy with the lower cost to install the system, but a year on I have been happy with the warmth, cooling and dehumidifying performance. I even reclaimed a double pole breaker on the electrical panel where there used to be a second HVAC system.
Even if you have to run some simple duct runs, it might still be cheaper and more efficient to use a more traditional forced air system than mini-split...even with the addition of ducts. Also, are you pouring a slab in side? If so, you might consider putting radiant heat in the floor (assuming you are pouring a slab inside)--you don't even need running water in the shop. I have a friend who did so with a small apartment sized hot water heater he filled once at install from jugs and then it just runs as a closed loop.
I live in Southern Michigan also. I have a 32'x56' pole barn with 10' ceilings. 8" of cellulose insulation the wall and 15" in the ceilings. I have a hanging unit heater rated at 120,000 btu's. It does an excellent job of heating my shop even in the occasional sub zero day. The insulation does a great job of keeping it cool in the summer.
I have an LG mini split in my shop. Am located in central MO so get hot days in the summer (was right at 100 today) with humidity and cold days in the winter. My mini split does an excellent job at keeping a very comfortable temp regardless of what is going on outside. I purchased mine thru ecomfort.com. Called them with the specs (shop is 900 sq ft with 10 ft ceilings), spray foam insulation in walls and ceiling. They did the work on making sure I got the right sized unit. Fast shipping and was installed by a local HVAC person. Would highly recommend this as a solution.