Single-zone minisplit for 24X35 workshop possible?

[tpcolson]

Getting ready to rehab my 3 bay, detached garage, 35X24X10 workshop. I predominantly do wood working in there, but I also wrench on the truck, etc, so it's really multipurpose. East TN, part of the rehab is to "better" insulate the walls (6") and put in a ceiling, etc. Assuming I do insulated garage doors, R19 on the walls, and let's say R30ish for the ceiling, is a single zone minisplit gonna suffice? The problem I have is available load in the panel. I need 3 GP circuits for my tools, 1 240V circuit for the floor tools, and a lighting/garage door opener circuit. That leaves me 20 amps for HVAC. That number is not going to change, according to the inspector when I initially wired the shop.

My only goal is to not have to wear hat and gloves (or see my breath) in the winter, or sweat so much it ruins the finish I'm applying to a piece of wood in the summer, both conditions which exist now, with a priority towards getting some heat in there. Every dual zone I look at for that square footage needs more than 20 amps, but many posts on this forum suggest a single zone isn't going to do much for that space. Again, just looking to able to work in there in the winter without having to dress up like I'm going ice skating. I can spend a few extra bucks on insulation: upgrading the wire to the sub panel or reducing the # of tool circuits to free up more load for HVAC isn't possible. I considered one of those ceiling-mounted radiant heaters, but I figured if I'm going to be pulling that many amps, might as well get some AC in the summer as well!

 

[PoorUB]

I don't know why a single zone mini split would not work. I have a 24x38x9 shop and I cooled it with a 12,000 BTU window shaker for years. Put in a single head min split and add a ceiling fan if you can.

It isn't like one end of the shop will be 50 degrees and the other at 70 degrees! You might notice a slight 1-2 degree difference from on end of the shop to the other, but it will cool and heat just fine for the purpose. It is a shop, not a home.

 

[Syberia]

Not sure what your inspector is basing their limitation on, but it doesn't seem correct to me. How many amps is the subpanel? If you know you're not going to overload it with your expected use, personally I wouldn't involve the inspector at all.

 

[tpcolson]

Not sure what your inspector is basing their limitation on, but it doesn't seem correct to me. How many amps is the subpanel? If you know you're not going to overload it with your expected use, personally I wouldn't involve the inspector at all.

60 AMP panel, when the shop (and the whole house) was rewired, including new meter, main panel, and subpanel in shop, a 20 amp double pole was left blank in the shop panel and listed on the permit as "Future HVAC". 8 GA wire from house to shop. Inspector specifically said "Good, that's the limit of what I'll approve if you ever decide to install one, and don't forget to pull another electric permit when you do". Electric permit is required for new HVAC install in my county, or if your replacing one fuel type with another (e.g LP to heat pump). I'm not one to argue with the inspector unless he's clearly and verifiably wrong. One of the 20 amp circuits is dedicated dust collector (18 amps on start up, peak 15 at continuous load), so really can't put much else on that one, and I generally come close to pushing the other two with all of the other tools, fans, and chargers I run. Floor tool(s) pull 12 max on the 20/240 they're on. I really don't see where there's enough load left to run a 30 or 40 amp HVAC unit.

 

[tpcolson]

I don't know why a single zone mini split would not work. I have a 24x38x9 shop and I cooled it with a 12,000 BTU window shaker for years. Put in a single head min split and add a ceiling fan if you can.

It isn't like one end of the shop will be 50 degrees and the other at 70 degrees! You might notice a slight 1-2 degree difference from on end of the shop to the other, but it will cool and heat just fine for the purpose. It is a shop, not a home.

That sounds perfect. Hell, I can deal with a 10 degree difference, as long as in the winter when I'm in the lower 10 part of the shop I don't have to wear gloves.....

 

[u2slow]

My heat-pump can only make enough heat in the shoulder seasons, not in winter. Multiple zones is the strength of a mini-split arrangement, but for a single space you may as well use a large window unit, or pass-thru wall unit.

If what you want is to take the edge off when it's truly cold, see what you get out of a 4kW of resistive heat, otherwise you need to burn fuel.

 

[PoorUB]

My heat-pump can only make enough heat in the shoulder seasons, not in winter. Multiple zones is the strength of a mini-split arrangement, but for a single space you may as well use a large window unit, or pass-thru wall unit.

If what you want is to take the edge off when it's truly cold, see what you get out of a 4kW of resistive heat, otherwise you need to burn fuel.

Good advice for the northerners, but he lives in Tennessee. and 18K HP will work fine in his situation., maybe even a 12K.

 

[MushCreek]

A lot of it depends upon how tight and well insulated the space is. Our house is 1400 sq ft, and we use a single 12K mini. Our climate is probably slightly warmer than you, but not much. But- our house is ICF construction with R50 in the attic, and it's a very tight structure. Air infiltration will kill the efficiency, so try to tighten it up as much as you can. My shop is about the size of yours, and not nearly as snug as the house. I plan to run an 18K.

 

[vavet]

I have a 24x32 x 12....roughly the same cubic footage in roughly the same climate. My 18k mini split is near the middle of the 32' wall. Its amazing. It calls for 12 ga wire and 20 amps at 240v.
Sounds like that is exactly what you need

MRCOOL Olympus ENERGY STAR 18,000 BTU 1.5 Ton Ductless Mini Split Air Conditioner and Heat Pump - 230V/60Hz O-ES-18-HP-230E - The Home Depot

MrCool's 20.8 SEER 18k BTU Olympus Energy Star Series Ductless Heat Pump combines excellent efficiency with a completely modern unit that pairs seamlessly with MrCool's own smartphone app, Google Assistant,

www.homedepot.com

BTW, this is nearly 2x as much as I paid for the Advantage model (now out of stock) in 2019.

 

[dlwilson]

I have a 24x40 space with a 36K BTU mini-split with dual air handlers. It is way overkill. It will drop the temp in south Florida to a comfortable level in 15 minutes.

https://www.amazon.com/gp/product/B00UV3LLB8/?tag=atomicindus08-20

 

[jeremybarnes]

I'm just south of Nashville, so similar climate as the OP -- a few days below freezing in the winter, a few days over 100 in the summer but lots of humidity to deal with.

I have a 35x40 metal shop with two really well insulated 10x12 roll-up doors, a thick man-door and three double-glazed opening windows.

Ceiling is completely open to the 20' peak inside, with 2" of spray foam on the ceiling (R40 or so, i'm guessing) and contractor-grade bubble wrap insulation (R7, according to the company that built my shop) on the walls. I have a Mr Cool DIY 36k and it keeps the shop at 75 all summer long with no issues. It struggles in the winter, i'll be honest, so I set the thermostat to 60 (the lowest it'll go to), and it keeps the building around 45 or so at the opposite wall from the fan-head. I don't think there's any way I could get the heat up to 70 in the winter, if I wanted/needed it.

I keep classic cars in the shop, so freeze protection is critical, and my system does all I need it to do for me. Would like to add foam to the walls at some point, but it's a nice-to-have not a have-to-have. Foaming the ceiling made a massive difference, in and of itself, and, other than the combination of all the other upgrades (better doors and windows), it's the single biggest improvement I made.

Hope this helps.

 

[PoorUB]

I'm just south of Nashville, so similar climate as the OP -- a few days below freezing in the winter, a few days over 100 in the summer but lots of humidity to deal with.

I have a 35x40 metal shop with two really well insulated 10x12 roll-up doors, a thick man-door and three double-glazed opening windows.

Ceiling is completely open to the 20' peak inside,

You have 1-2/3rds the floor space and a 20 foot peak that is a bunch more than the OP has to deal with.

I mentioned cooling my 24x38 shop with a 12,000 BTU window shaker. It would cool the shop fine in 100 degree heat as long as i started and left it run so it would catch up over night. If I let the shop warm up and turned on the AC in the afternoon it would not catch up until the outdoor temps dropped. He has about the same size as I do and I would go with a 18K mini split for cooling, maybe a 24K considering the heating side, but one needs to find out the specs on the unit they plan on buying. Some 18K will get you 18K of heat at +5F, some only 9K.

 

[Jackfre]

You can run a 24k dual or triple Fujitsu on 20A. You could also do an 18 or 24 single on 20A. With a 4 way air sweep on the singles it would do the job. Welcome aboard, btw. I have to say it is easiest for folks to help especially with climate control issues if we know kinda where you are.

 

[tmshort]

@tpcolson
I have a 24x36x10 in Indiana. Insulated, but not as well as I would like (stick build 2x4 with standard batts, 2x single garage doors and 2x man doors, both of which need replaced). I also have an upstairs area of similar size.

I put a single 18K BTU Pioneer in the downstairs back in May or so. It easily kept the space at 75F all summer, and cooler if I wanted (without running even close to all the time). And this is with the stairs to the second story wide open. Upstairs got warm in the summer.

I just added a second 18k BTU unit upstairs last week so that I can effectively heat and cool both spaces.

Based on mine, I bet a single unit would work fine for you. I have 2 ceiling fans in the downstairs to circulate air which may help some, but once the space was cooled to whatever I set it stayed there no problem.

 

[3rdgendslmech]

I put in a MR.Cool DIY 24K unit for my 24x32x10 pole barn and it keeps it comfortable to work in summer and winter. Right now i've only got the walls insulated. Still working on the split door and roof insulation.