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Ductless Mini Split for Attached Garage?

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[OP]
Deal Addict
Nov 8, 2005
2783 posts
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Ductless Mini Split for Attached Garage?

Hey guys,

Wondering if anyone has any experience with ductless mini splits to heat an attached garage? Trying to find an energy efficient and low priced option to heat my garage in the winter and air conditioner it in the summer. Wondering if these are up to par for the wild swings in weather we have? Open to other suggestions as well of course.
19 replies
Deal Addict
Nov 17, 2012
3662 posts
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Toronto
Size it right for the space and insulate, and of course it will work. Just like indoors.

FWIW I have a 12 x 20 old wood framed garage (2x4, built in the 30's probably) that I insulated with some cheap used (really) insulation and sheathed with OSB on the interior. Didn't bother insulating the ceiling. No windows, insulated garage door and steel entry door.

I have a 5000w 240v construction heater I use in the winter, and I cut a hole in the wall and have a window AC unit for the summer. Does just fine and probably cost me $200 combined getting the heater and AC used.

I tend to heat/cool it in the evening and on weekends when power is cheap. I don't keep the garage at a particular temp year round - that would be expensive, and insane unless you're retired and spend all day every day in the garage and have the income to cover the extra utility costs.

You haven't mentioned anything about size, what part of the country you're in, construction, insulation...

Figure spending $3,000+ on a split unit from what I've seen.
Member
Mar 25, 2012
238 posts
34 upvotes
Ottawa
I got a hot dog natural gas heater to heat my 12x20 garage a few years ago and it's been great. I think it costs somewhere around $1,500 maybe 2000 including installation. I keep the garage at 5° in the winter or so unless I'm going to be staying there for a couple of hours or so. It's fully insulated including the ceiling. It can get a bit hot in the summer but not too bad I open the door window.
Deal Guru
Jan 25, 2007
10843 posts
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Paris
I have a Mr Heater big Maxx and my next garage will be a mini split.
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Oct 19, 2008
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tim-x wrote: Wondering if anyone has any experience with ductless mini splits to heat an attached garage? Trying to find an energy efficient and low priced option to heat my garage in the winter and air conditioner it in the summer. Wondering if these are up to par for the wild swings in weather we have?
.Mini split will work great in the summer to cool the garage down, sealing doors and insulation would keep costs down. Most mini splits aren't great as heaters, not very efficient once the temps dip below -5*c and many don't heat when temp is below -12*c. Mini splits are more energy efficient than a space heater from -5* to 10*, you might consider installing a decent oil filled electric heater (safe) and a mini split.
Those are general figures, there are mini splits that heat when outside temps are below -12c....and some that don't heat at all.
Deal Guru
Jan 25, 2007
10843 posts
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Paris
If I was building from scratch I would do a hot water system in the floor to maintain 10 degrees celsius, and a mini-split to top up. I was working on an ATV once in the garage when it was -20 outside and the garage at my head was 20 celsius, the floor was still around 3 degrees. A ceiling fan makes a big difference to stir up the air, but garage heaters all draw hot air from the ceiling in vs the cold from the floor. Once guy I know who uses his garage for his living used some hvac tin to make the garage heater draw from the floor.
[OP]
Deal Addict
Nov 8, 2005
2783 posts
1835 upvotes
Jerico wrote: I have a Mr Heater big Maxx and my next garage will be a mini split.
Do you not like this? Thats what I'm looking at right now. But as a poster already mentioned here general consensus is that mini splits aren't that effective or efficient at low Temps. I've seen ones like the Senvilles that are advertised to -30 C which seems crazy.
[OP]
Deal Addict
Nov 8, 2005
2783 posts
1835 upvotes
torontotim wrote: Size it right for the space and insulate, and of course it will work. Just like indoors.

FWIW I have a 12 x 20 old wood framed garage (2x4, built in the 30's probably) that I insulated with some cheap used (really) insulation and sheathed with OSB on the interior. Didn't bother insulating the ceiling. No windows, insulated garage door and steel entry door.

I have a 5000w 240v construction heater I use in the winter, and I cut a hole in the wall and have a window AC unit for the summer. Does just fine and probably cost me $200 combined getting the heater and AC used.

I tend to heat/cool it in the evening and on weekends when power is cheap. I don't keep the garage at a particular temp year round - that would be expensive, and insane unless you're retired and spend all day every day in the garage and have the income to cover the extra utility costs.

You haven't mentioned anything about size, what part of the country you're in, construction, insulation...

Figure spending $3,000+ on a split unit from what I've seen.
Sorry I should have given more info.

It's an attached double car garage with a fiberglass uninsured garage door. No windows and 1 exterior door. Approximately 20x17. It has one wall thats exterior where 75% of it is sheathed with foamboard and then pink fiberglass Batts. The other 25% is sheathed with osb with pink fiberglass Batts in the bays. The other 2 walls are interior walls that have foamboard and then pink Batts. Above the garage is the master bedroom so basically everything is insulated except the concrete slab and the garage door, which is sealed with weatherstripping.

I want to use this as a living space. Planning on finishing the floor and putting a couch out there with a TV and some workout equipment.

I'm located in Southwestern Ontario where winters are actually generally not that harsh (generally between 0 to -15C but they can be depending on the winter. Summers get pretty hot: +30 C

I saw this Senville is quite cheap and is advertised to -30C. There has to be a catch?

https://senville.ca/12000-btu-mini-spli ... sena-12hf/
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Oct 19, 2008
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tim-x wrote: I saw this Senville is quite cheap and is advertised to -30C. There has to be a catch?
Yeah, catch is at those lower temps its not the energy efficient heat pump producing heat....electric coils kick in (like a space heater) to produce heat. Not terrible as long as you know what to expect (higher electric consumption).
Sr. Member
Feb 27, 2007
528 posts
325 upvotes
Zamboni wrote: Yeah, catch is at those lower temps its not the energy efficient heat pump producing heat....electric coils kick in (like a space heater) to produce heat. Not terrible as long as you know what to expect (higher electric consumption).
The unit he listed has a COP W/W of 3.55 so if I'm remembering my schooling it'll still be producing heat from the heat pump at -30C at a rate more efficient than pure electric heat.

It won't be beating it by much but it should still be off the heating strip.
[OP]
Deal Addict
Nov 8, 2005
2783 posts
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von Monster wrote: The unit he listed has a COP W/W of 3.55 so if I'm remembering my schooling it'll still be producing heat from the heat pump at -30C at a rate more efficient than pure electric heat.

It won't be beating it by much but it should still be off the heating strip.
Man if it's -30 C I doubt I'll be in my garage, heated or not.

You definitely sound like you know what you're talking about. Is this unit reasonable for an insulated attached garage for a southwestern ontario winter? My other option is to get a natural gas heater like the Mr. Heater ones and then get a mini split air conditioner only. Much higher upfront cost doing it that way.
Sr. Member
Jan 19, 2013
631 posts
453 upvotes
Ottawa
von Monster wrote: The unit he listed has a COP W/W of 3.55 so if I'm remembering my schooling it'll still be producing heat from the heat pump at -30C at a rate more efficient than pure electric heat.

It won't be beating it by much but it should still be off the heating strip.
COP of 3.55 is standard test at 47f (8c) outdoor temp
Senville doesnt publish the COP at lower temperatures like other manufacturers do, so who knows what it is.
At -15c i would guess to be at 1.7 and fall off pretty quick any lower than that
Sr. Member
Jan 19, 2013
631 posts
453 upvotes
Ottawa
Dont know this specific unit, but keep in mind most mini split manufacuters, the lowest heat set point is around 60f or 15c
Probably a bit expensive to keep the garage at that temperature unless youre in there doing stuff everyday
[OP]
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Nov 8, 2005
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1chinaman wrote: COP of 3.55 is standard test at 47f (8c) outdoor temp
Senville doesnt publish the COP at lower temperatures like other manufacturers do, so who knows what it is.
At -15c i would guess to be at 1.7 and fall off pretty quick any lower than that
Is that bad?
[OP]
Deal Addict
Nov 8, 2005
2783 posts
1835 upvotes
1chinaman wrote: Dont know this specific unit, but keep in mind most mini split manufacuters, the lowest heat set point is around 60f or 15c
Probably a bit expensive to keep the garage at that temperature unless youre in there doing stuff everyday
I did not know that. I'd probably just be turning it on when I'm in there.
Sr. Member
Jan 19, 2013
631 posts
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Ottawa
tim-x wrote:
Is that bad?
Pretty normal, just as it gets closer to 1 COP, you might as well use electric resistance heat.
No point trying to push a $2000 system in -25c to get like a COP just above 1.
Just use your $100 electric construction heater

tim-x wrote: I did not know that. I'd probably just be turning it on when I'm in there.
Your going to need a way bigger heat pump if your going to do that or you ll wating a while in the winter time
This 12k senville only rated to put out 7800btu/h at -8.3c ouside
To put that in perspective, the 115 volt room heaters you plug in puts out 5000btu/h
Deal Guru
Jan 25, 2007
10843 posts
6105 upvotes
Paris
tim-x wrote: Do you not like this? Thats what I'm looking at right now. But as a poster already mentioned here general consensus is that mini splits aren't that effective or efficient at low Temps. I've seen ones like the Senvilles that are advertised to -30 C which seems crazy.
I like it just fine. When I installed it I had some incorrect assumptions. The biggest one is that I would use it on demand, and thus need to heat from nothing to 17ish celsius. As soon as I got it and realized how cheap it was to run, I left the garage 10 degrees all the time. No need to have something that heats that quickly. Plus, I wanted to use my garage in the summer for things and the heater did nothing for the humidity.

If you are planning on using this as living space, do NOT get a Mr Heater or Hot Dawg or any of their ilk. They are loud and annoying and rough. I could not watch TV in my garage with the Mr Heater running. Its fine for using power tools etc, but would drive me batty for watching TV.
Deal Addict
Nov 17, 2012
3662 posts
2687 upvotes
Toronto
Propane fired heaters are also not certified for indoor use in Canada. The idea of using one in a closed room is nutty.

Kill two birds with one nickel. Run a 40A circuit to the garage, install a subpanel and get a 220v electric heater. You'll have power for welding and other uses when you're not heating. If you have 200A service at your home, then run even more power to the garage so you can weld and heat at the same time.

Invest in the power delivery, then use cheap portable AC/construction heater to condition the space.
Deal Addict
Nov 17, 2004
3003 posts
1240 upvotes
Jerico wrote: I like it just fine. When I installed it I had some incorrect assumptions. The biggest one is that I would use it on demand, and thus need to heat from nothing to 17ish celsius. As soon as I got it and realized how cheap it was to run, I left the garage 10 degrees all the time. No need to have something that heats that quickly. Plus, I wanted to use my garage in the summer for things and the heater did nothing for the humidity.

If you are planning on using this as living space, do NOT get a Mr Heater or Hot Dawg or any of their ilk. They are loud and annoying and rough. I could not watch TV in my garage with the Mr Heater running. Its fine for using power tools etc, but would drive me batty for watching TV.
I’m glad to hear that I’m not the only person that thinks it’s cheap to run an NG heater in the garage. I go a bit overboard maybe, but I keep my garage a bit below 15C in the winter (depending on how accurate the analog thermostat is) to keep my vehicles warm (DD, track car and motorcycle) so that I don’t really have to winterize my parked vehicles. It’s basically pennies for the heater to kick in for 5-10 mins every hour.

And yes...definitely quite loud as well. Not a problem for me since i wrench in my garage and I just have my EarPods in, but it can be loud enough that it’s hard to hold a conversation with somebody else. Throw in a big compressor going at the same time and it’s really quite loud in the garage.

And for OP’s consideration, depending on how set you are on getting AC in the summer as well, it may be worth thinking about an NG heater for the winter and a nice big fan for the summer. I run a big shop fan in the summer to move the air around and with both garage doors open, it’s pretty okay.

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