Mini-split for Midwest winters?

[Jim Dawson]

I just moved and am trying to figure out heat and air for my detached garage. My previous garage was 24X24 with a 10' ceiling. I had a conventional electric furnace with air and it worked great for both summer and winter here in the St. Louis area.

My current garage is 24X24 with an 8 1/2' ceiling, both walls and attic are well insulated but unfortunately unheated. I am going to be limited to an electric only solution and am looking at a mini-split as it looks like I could use my existing 50A service by adding a 30A breaker. If I go the conventional furnace/AC route I'd have to spend a lot of money upgrading the electric service and spending considerable more money for the system.

My question is, will a 24,000 BTU mini-split give me enough heat in the cold mid west winters? There are some pretty inexpensive systems available that look like I could install myself.

Below what temperature will the heat pump no longer heat well?

Thanks for any advice,
Jim

 

[theoldwizard1]

My question is, will a 24,000 BTU mini-split give me enough heat in the cold mid west winters? There are some pretty inexpensive systems available that look like I could install myself.

Below what temperature will the heat pump no longer heat well?

Your last question is the key !

Some "better quality" heat pumps (Mitsubishi) will run at 100% efficiency down to about 0F. Others start dropping off somewhere around 40-50F.

View media item 43975
You will pay more these systems, but that is what you want.

I would buy some kind of portable heater (propane/oil) for those nights when it get below zero.

 

[Radix2]

I just bought a Gree Crown 12kbtu mini split to install in a beach cottage on Lake Huron, according to the submittal sheet it will still produce 10kbtu of heat at -22F. Place has a 9kbtu electric wall heater that should never have to be used... I'll do a post on it when it gets installed since there is not much on the hyper heat units on here.

 

[Jim Dawson]

Wow, the price difference between the Mitsubishi and the cheap ones might make buying a portable supplemental heater a good choice.

 

[crabjoe]

A heat pump, regardless of it being properly sized may work or might not work for a give space... What I mean is that Heat Pump A might work in your friends place of the same size, but not in your place. It really depends on leakage... If your garage really leaks, the heat pump will have a harder and harder time trying to keep up versus a place that's air tight, at the same volume.

So it's hard to say at what temp a heat pump will stop working... for a given volume.

 

[theoldwizard1]

I just bought a Gree Crown 12kbtu mini split to install in a beach cottage on Lake Huron, according to the submittal sheet it will still produce 10kbtu of heat at -22F. Place has a 9kbtu electric wall heater that should never have to be used... I'll do a post on it when it gets installed since there is not much on the hyper heat units on here.

I will admit, I am not an HVAC guy, but checking the spec sheet on that unit is see this. which does not line up with what you quoted.

 

[HoosierBuddy]

Garages present some special challenges to heating.

The fact they may not be insulated that well and they are going to experience air infiltration around the doors is obvious.

What may be less obvious is that many of us USE our garage heat vastly differently than we do our home's heat. We turn it off or at least down to a low temperature when we are not in the garage and then turn it up on Saturday when we have a project to do (at last that's what I do).

The heat up places extra load on whatever heat source you are working with. This may not be a big deal if you have a big honking hanging gas fired unit heater, but it may be a challenge for a marginally sized radiant system, an undersized electric heater or a smallish heat pump.

Heat pumps in general simply don't have that extra capacity to jump in and take a space from 45 degrees to 65 degrees in a reasonable time. That's why older heat pump systems typically include a supplemental resistance electrical heating element to help in these situations. I'm not sure if your mini-splits include that feature though. The awful downside (if they do) is that when the strip comes in, it increases the cost/BTU by about 400%.

So...those of you that DO have heat pumps (especially if marginal) might be better off setting your garage temperature at a median temperature you can live with (like 52 degrees or so) and just leave it there all winter. It might not be as comfortable, but it would be a lot easier for your heat pump to keep up.

The big advantage of the heat pump would be the AC in the summer. I know in my case, it can get so unbearably hot in my garage or barn that I will avoid working out there for weeks on end sometimes.

Phil

 

[Radix2]

I will admit, I am not an HVAC guy, but checking the spec sheet on that unit is see this. which does not line up with what you quoted.

What do you see on page 2 ?

 

[Jackfre]

At -22 I see nothing. At 17* I see 8500btu (COP of 2 X 3414 btu/kw +some fudge I guess). The max 12kbtu number confuses me. Heat pumps are tested at the 47 & 17* temps. If I was basing the decision on low temp heating I would want to see the output curve across the temp range. Gree has that and it should be available. The Mitsu chart that TOW1 posted is what you want. Low temp heat pump operation is or can be the classic example of "figures don't lie, but liars figure." Mitsubishi and Fujitsu do the low temp heat reliably. The other thing is that they both have real tech support and parts. You pay for it. If the Gree is cheap enough and mini-splits become less and less expensive they may join the "disposable appliance" category where the are just replaced rather than being fixed.
I don't know how your garage is built, but a 24 is twice what you need for cooling. I know folks pick them for heat, but in your humid climate gross oversizing creates problems with dehumidification. Unless you can throw the ca out through the cracks in the place I'd go with an 18.

 

[theoldwizard1]

The heat up places extra load on whatever heat source you are working with. This may not be a big deal if you have a big honking hanging gas fired unit heater, but it may be a challenge for a marginally sized radiant system, an undersized electric heater or a smallish heat pump.

So, are you saying that most gas fired heating systems are oversized ?

Heat pumps in general simply don't have that extra capacity to jump in and take a space from 45 degrees to 65 degrees in a reasonable time. That's why older heat pump systems typically include a supplemental resistance electrical heating element to help in these situations.

NOT TRUE ! Older heat pump systems have resistance elements because the can not extract "heat" from temps below about 45F. Modern mini-splits can extract heat from much colder ambient temperatures.

The big advantage of the heat pump would be the AC in the summer. I know in my case, it can get so unbearably hot in my garage or barn that I will avoid working out there for weeks on end sometimes.

While a "free" A/C system is nice, it is NOT the main reasons for purchasing a mini-split. Mini-split systems are incredibly EFFICIENT ! Mini-slit systems come other parts of the world where a typical residence only has a few rooms to heat/cool so they work well in a single room (garage) situation.

While solid fuel (wood, coal) and natural gas are still probably the cheapest fuels, a good mini-split is more cost effective than electric resistance, propane or oil. Yes, it will take a few years to recover the installation cost but after that it is all money in your pocket.

 

[Radix2]

At -22 I see nothing. At 17* I see 8500btu (COP of 2 X 3414 btu/kw +some fudge I guess). The max 12kbtu number confuses me. Heat pumps are tested at the 47 & 17* temps. If I was basing the decision on low temp heating I would want to see the output curve across the temp range. Gree has that and it should be available. The Mitsu chart that TOW1 posted is what you want. Low temp heat pump operation is or can be the classic example of "figures don't lie, but liars figure." Mitsubishi and Fujitsu do the low temp heat reliably. The other thing is that they both have real tech support and parts. You pay for it. If the Gree is cheap enough and mini-splits become less and less expensive they may join the "disposable appliance" category where the are just replaced rather than being fixed.
I don't know how your garage is built, but a 24 is twice what you need for cooling. I know folks pick them for heat, but in your humid climate gross oversizing creates problems with dehumidification. Unless you can throw the ca out through the cracks in the place I'd go with an 18.

Do you guys have a problem looking at page 2 of the submittal that wizard posted? - the output across the temperature range is there in black and white, more data than is available from most manufacturers. I have not quite figured out the difference between maximum performance shown on the submittal said vs the rated performance, it looks to be differences based on inlet air temps and may also have to do with losses associated with defrost at low temps?

The guy with the Gree is not the guy with the garage.

 

[Jackfre]

Thanks for pointing that out. Apparently I have a problem looking at page 2

 

[Jim Dawson]

I think I'm going with the Panasonic http://www.alpinehomeair.com/viewproduct.cfm?productID=453068956
Unless someone has negative info about Panasonic that I should be aware of.

 

[theoldwizard1]

I think I'm going with the Panasonic http://www.alpinehomeair.com/viewproduct.cfm?productID=453068956
Unless someone has negative info about Panasonic that I should be aware of.

Not the best in the industry for low ambient heating. You will need auxiliary heating for those really cold days/nights.

 

[Jim Dawson]

I guess I don't know what I'm looking at with those numbers. What would a really good chart look like and what system would do what I need?

 

[Jim Dawson]

Is this a better looking chart? This is from the Mitsubishi MZ-FH15NA .

 

[Jim Dawson]

I guess I don't know how to post the picture and not the thumbnail - grrr.

 

[Radix2]

I guess I don't know how to post the picture and not the thumbnail - grrr.

The thumbnail works fine to bring up the full picture.

The numbers to look at are the minimum temp for heating. Are you still in St. Louis ? So the Mitsubishi that goes to below zero is better than the Panasonic (which looks better than the typical unit that goes to 5f or so.). I would think in St. Louis that you don't have many below zero F days? Will you have any critical things like water pipes that could freeze on a rare super cold day?

Doh, now see you are in Illinois, so the winter needs will be more stout.. Still the question is how critical on the rare cold snap.

 

[Jim Dawson]

The thumbnail works fine to bring up the full picture.

The numbers to look at are the minimum temp for heating. Are you still in St. Louis ? So the Mitsubishi that goes to below zero is better than the Panasonic (which looks better than the typical unit that goes to 5f or so.). I would think in St. Louis that you don't have many below zero F days? Will you have any critical things like water pipes that could freeze on a rare super cold day?

Doh, now see you are in Illinois, so the winter needs will be more stout.. Still the question is how critical on the rare cold snap.

Thanks for the help. I'm in Illinois but in the St. Louis metro area. I just ordered the Mitsubishi MZ-FH15NA so I'll se how that does. We only have a few really cold snaps per year but I want to be warm through them so I spent the few extra $. If their performance numbers hold up it should do what I need.

 

[theoldwizard1]

Thanks for the help. I'm in Illinois but in the St. Louis metro area. I just ordered the Mitsubishi MZ-FH15NA so I'll se how that does. We only have a few really cold snaps per year but I want to be warm through them so I spent the few extra $. If their performance numbers hold up it should do what I need.

I think you made the right choice, especially if the Mitsubishi model is only "a few extra dollars". Further north of you (northern MN, WI, MI) you would have to have some type of auxiliary heat.

 

[Jim Dawson]

I think you made the right choice, especially if the Mitsubishi model is only "a few extra dollars". Further north of you (northern MN, WI, MI) you would have to have some type of auxiliary heat.

I guess I may have told my wife it was only "a few extra dollars". It was really more like $300 more but I think it'll be worth it.

Thanks for the help.