Mini split compressor questions

[Mark in Baltimore]

Hi,

Been doing lots of research here for several months as I am planning on finishing my garage. I want to add a Mitsubishi MSZ-GL12NAUI (inside unit) and MUZ-GL12NAU1 (heat pump) in my 22' L x 19' W x 9' H garage. (I'm going to have the roof deck and walls spray foamed with closed cell foam; did it to the attic and rim joist of our house and am amazed at the insulating qualities.)

• Does this unit meet the standards for the size of the garage as well as our Maryland climate?

• I have a price of $3950 installed (not including a utility rebate of $360); is $3590 a decent price?

Two contractors suggested I have a small pad built/poured so that the compressor is level. However, I have seen compressors mounted on brackets like this:

http://www.homedepot.com/p/Ductless...Conditioners-and-Heat-Pumps-BPC-3LP/205886666

$45-$75 for a bracket is much cheaper and easier than paying someone to level out the ground and make a small retaining wall for the hill next to the garage.

• Will this compressor generate too much vibration if mounted to the studs? I think it can be mounted into the poured concrete wall, but it's perhaps a bit lower than I would like (snow clearance) but better than a ground pad.

• One of the contractors said that the compressor needs to be mounted 12" away from the wall, but the mounts seem to only allow about 6" of clearance; will I be compromising the unit and/or efficiency by mounting it 6" away? I'm assuming the wall-side is the intake side, so I can't imagine that the air exchange with 6" of clearance is that big of a deal.

• Do compressors generate too much heat for my vinyl siding? I was told that the compressor needs to be about a foot away from the wall; the Home Depot one puts it 10" away which I figure is good enough.

Sorry if these are noob questions; checked the archives and only saw a few posts on this matter.

Thanks for any help!

 

[Pziddy29]

This unit should do the job as your square footage is roughly 417 sq ft


Sent from my iPhone using Tapatalk

 

[Firebrick43]

If you spray foam it I think you will actually be oversized, but that will be ok to cool a hot car.

I would suggest not spray foaming the roof deck. A hot roof can be done but they always have moisture issues. Over time the roof deck will be compromised at an accelerated rate and when replaced you then have to reinsulate. It also accelerates the deterioration of shingles and most manufactures will not warranty them over a non ventilated deck.

 

[Walter_TA]

Go to AC wholesaler and take a look at there price. I think you are paying 2500 for the install. From what I have seen the install for a heat pump is not that hard. Many will buy the system and install it, and just pay to have it vacuum pumped and started. I plan to do it all myself. As as far as wall mounting you have to look at the directions for the unit. Most recommend 12 in but a min of 4.

 

[yeldogt]

If you spray foam it I think you will actually be oversized, but that will be ok to cool a hot car.

I would suggest not spray foaming the roof deck. A hot roof can be done but they always have moisture issues. Over time the roof deck will be compromised at an accelerated rate and when replaced you then have to reinsulate. It also accelerates the deterioration of shingles and most manufactures will not warranty them over a non ventilated deck.

This is not the case .. spray foam on decks is not a problem and is a recognized/ code compliant. lots of information available -- GAF finally agreed in 2015.

I did my first unvented back almost 25 years ago -- and the 40 year presidential asphalt shingles look "as new" when added on to the building about 8 years ago w/ matching product.

I only use closed cell.

 

[yeldogt]

The MSZ is the best indoor unit -- with the eye. Really, a great system. It goes for upwards of 1k Plus the outside unit and all the sealed items needed. ... is that the hyper heat outside compressor? That's about the going price -- did you get other estimates?

The HP will need the stand if on a pad -- the unit blows out -- so it ***** from the sides and behind. No worries near the house

I have a three head hyper heat mounted on my brick exterior and I get a slight vibration in the heat pump mode when it's ramping around out there. I'm building a new place and I'm going to mount that one on a pad -- same 30k unit in both places. Now -- I'm being picky .. as I could hear the old units ... but .... my guess is if on a pad it would be silent. Most of the time I have to look to see if the fan is spinning.

It may be different with a stud wall/ foam --- My guess is it will not be a problem if you mounted on the wall. Many many are done that way. They are more noticeable on the wall (visually) -- but no danger of any snow build up and they sit within the roof over hang -- so safe from rain run off if gutters clogged.

With spray foam 1T should be great.

 

[Fueler]

I will try to answer the mounting questions based on my own AC diy installation experience.

The 12K units are not real heavy so the wall brackets sold will do the trick.
Try to find studs to mount to and level it real well. Maybe just a tick up bubble before the unit is bolted down. A second thought if the wall is still accessible and you are not hitting the studs add some cross boards between the studs to seal the deal.

The sold bracket always put the unit closer than they recommend but I don't see any followup reviews complaining of melted siding issues.

I do have one issue. I need to clean the back side of my 36K unit of accumulated dust and grunge. It is closer to the wall than desired and will be fun to clean, not/

IF you live in blowing leaf or blowing snow country you definitely want it off the ground and preferably away from prevailing winds. The east side works well for me.

The heat output is not real intense so I don't expect siding issues.
That said if it worries you fab up a set of brackets to move it further away.

Vibration? No, these things are incredibly quiet and smooth running. I have to walk up to my 12K occasionally to verify it is running.

 

[soob]

I may not be in the majority but my opinion is that air conditioners for shops and garages ought to be larger than air conditioners for living spaces. The usual equations don't work. You want something that can cool or heat the space FAST for intermittent use. So go with a bigger one, IMO.

No the compressors don't get hot enough to melt anything. The wall brackets are fine; the FULL wall clearance behind isn't needed if there's no ground (so says the people that sell the brackets, anyway).

I put a mini split in recently and it was easy enough for me (a fairly competent DIYer). It requires only a couple hundred dollars worth of tools. I would not pay someone $3000 to install one.

 

[Marctrees]

Well, here I am again asking why spend that money discussed above rather than $500 - $600 window AC mounted in dedicated hole in wall?

How often will you be heating it in winter and what temp do you need inside is the only other issue to answer.

Marc

 

[Mark in Baltimore]

Thanks for the great responses! Really appreciate the feedback.

The MSZ is the best indoor unit -- with the eye. That's about the going price -- did you get other estimates?



I have a three head hyper heat mounted on my brick exterior and I get a slight vibration in the heat pump mode when it's ramping around out there.

You don't think the i-see sensor is overkill for a garage? I might spend two weekends a month max in there and figure just setting the thermostat will be fine for me. What am I missing?

And what is hyper heat?

I obtained only two bids.

Well, here I am again asking why spend that money discussed above rather than $500 - $600 window AC mounted in dedicated hole in wall?

How often will you be heating it in winter and what temp do you need inside is the only other issue to answer.

A window unit is not right for me for several reasons:

-Takes away too much natural light.

-Makes it easier to break into the garage.

-Our garage is detached and has a walkway near the sunroom. The AC unit would stick out and impede ingress and egress.

-The mini split offers heat that I understand is fairly efficient. I have a propane heater that kicks **** and will use that to jump start the heat. But once up to temperature, I want that thing turned off and out of there. My garage has limited space, and I've already melted some clothes by coming into contact with the heater. With the mini split, I can have the heat run at a nominal temperature to keep me from being uncomfortably cold.

 

[Ohmthis]

Mark, I agree with yeldogt, the mitsubishi's are very nice. The sensor won't really make a big difference, it's looking for body heat to direct the air. "Hyper Heat" is their fancy title for low ambient heating. They can make rated output down to below zero. You may be interested if it gets real cold there. Get as many quotes as you can and do research on not only the units, but the companies that are doing your install. Don't rule out Fujitsu or Daikin they are both very nice systems. Yes, the ductless systems are quiet and efficient, but they do have some cons. They are designed to maintain a consistent temp. They are not for quick pulls to high or low temps. They also don't filter very well. So if you woodwork, weld/grind, or just have a dusty/dirty shop you will want to clean the filter often. Let us know how it goes.

 

[yeldogt]

Hyper heats are designed to be the primary heat - so ...... they work down in very low temps (0 degrees) and still provide full capacity.

The eye comes on the best interior unit -- yes it's over kill ... but it does work. They make other wall units that have basic features and cost less ... the top unit has split vanes and moves the air around better vs the single output units. For the small price increase -- I bought the better units.

 

[justinjoyal]

If you have good (r20 or more in the walls, r40 or more in the attic) and nothing special like huge windows or uninsulated doors, 12k btu is really oversized for your space.

If you need quick recovery and dont care about comfort associated with lower relative humidity, then you will be fine.

The wall mounts you posted will work just fine. Don't worry about the reduced clearance. Make sure to you the rubber pads/shims they supply to reduce vibrations and don't tighten the bolts/screws too much.

Do you really need "hyper heat" units? Do you have backup heat?

Now, almost 4k $ for a mini-split like that is pretty much crazy IMO. But again, Mitsubishis are known to be overpriced.

 

[Mark in Baltimore]

Thanks much!

I checked my quote and saw that the $360 rebate was not included in my price, so the actual cost is $3590. I have another quote from another contractor for $3500. I assume the utility rebate of $360 applies, so that makes the cost $3140 fort this other contractor. I don't think this second guy is an HVAC specialist but just a general contractor. He didn't return a text message regarding the model of the unit, so, in conjunction with the fact that he doesn't specialize in HVAC, I've kind of written him off.

Mark, I agree with yeldogt, the mitsubishi's are very nice. The sensor won't really make a big difference, it's looking for body heat to direct the air. "Hyper Heat" is their fancy title for low ambient heating. They can make rated output down to below zero. You may be interested if it gets real cold there. Get as many quotes as you can and do research on not only the units, but the companies that are doing your install. Don't rule out Fujitsu or Daikin they are both very nice systems. Yes, the ductless systems are quiet and efficient, but they do have some cons. They are designed to maintain a consistent temp. They are not for quick pulls to high or low temps. They also don't filter very well. So if you woodwork, weld/grind, or just have a dusty/dirty shop you will want to clean the filter often. Let us know how it goes.

It can get as cold as 0 degrees Fahrenheit in Maryland. However, I don't plan on running the mini split in the winter. My propane heater will be utilized first and then I'll use the mini split to maintain the temperature. That's the plan for now at least.

I thought I had read here that Mitsubishi was kind of the reference standard for quality? I'd rather pay more for a super reliable system rather than go a less expensive route, only to compromise reliability.

Hyper heats are designed to be the primary heat - so ...... they work down in very low temps (0 degrees) and still provide full capacity.

The eye comes on the best interior unit -- yes it's over kill ... but it does work. They make other wall units that have basic features and cost less ... the top unit has split vanes and moves the air around better vs the single output units. For the small price increase -- I bought the better units.

What brand and models did you go with?

 

[Ohmthis]

Mark, I keep reading that this will only be a every so often used appliance. And while I believe that Mitsubishi is the gold standard, there are definitely VERY good options. That's why I added the other manufacturers. I always school on a ROI with HVAC equipment. The most expensive with all of the bells and whistles rarely break even over the course of their lifespan. I'm not trying to sway you one way or the other (I only use Mitsubishi for mini splits), but you need all the info available to you. Don't be afraid to look at other options. Both of the other two manufacturers have a low ambient heating option just like the "hyper heat". Let's all throw more ideas off each other.

 

[Marctrees]

Mark sed..."A window unit is not right for me for several reasons:

-Takes away too much natural light.

-Makes it easier to break into the garage.

-Our garage is detached and has a walkway near the sunroom. The AC unit would stick out and impede ingress and egress."

Well, I'm talking not in an exist window, but in a dedicated framed and trimmed hole with a sleeve AC filling it out and secured w screws in various correct places... NO way will that end up being the weak link break in point.

By the time a GJ Guy ends up walking away from a in wall install, it is secure as heck, and CANNOT be removed from the outside.


I'd be WAY more concerned about any existing window you may have as burglar access.


The last point about it being in the way, only you can decide how bad that is, meaning what it's worth.
And if there is no alternate location.

I just can't get over the roughly $3K price diff.

That can buy a helluvalot of shop stuff. Marc

 

[justinjoyal]

It can get as cold as 0 degrees Fahrenheit in Maryland. However, I don't plan on running the mini split in the winter. My propane heater will be utilized first and then I'll use the mini split to maintain the temperature. That's the plan for now at least.

I thought I had read here that Mitsubishi was kind of the reference standard for quality? I'd rather pay more for a super reliable system rather than go a less expensive route, only to compromise reliability.

Pretty much all mini-split provide adequate heat output at 0 F these days...

Why pay for "hyper heat" if you don't need it?

There are other brands out there that I would trust no less than Mitsubishi.

 

[Fueler]

Meh...., spent years growling about window units in my shops. Noisy, can't keep up and are usually toast within 3 years. The may say they put out X BTUs but I seriously doubt it. The fans certainly are undersize. There is a reason they are called room air conditioners.

The mini split, when you look at the size of the components and fans for the same BTU you too will begin to doubt the window unit advertising.

The mini split I now use literally blows them out the window so to speak. Absolutely no contest on any level. And for the record I went the DIY route. No problems. Slow and steady on the first one. Second one done in half the time.

 

[Mark in Baltimore]

Yep, there is the noise factor with window units. IME, they may start out quiet when first installed, but they often get noisier as they age. This is in addition to not providing efficient heat.

I may run the mini split all year round. My buddy here has a Mitsubishi without the i-see sensor nor the hyper heat. He says that his unit has not caused a noticeable increase in his electric bill, and this is with 24/7 use.

I'll have to do more research on the hyperheat option.

You guys are great! You've brought up features I knew nothing about.

 

[yeldogt]

I think you will find that running the HP will be cheaper vs propane .. what kind of propane heater? In all of my new build it's going to be HP with propane as backup and for radiant when it gets very cold.

Mini's all have VS compressors today -- even oversized using conventional figures the system will be able to adjust capacity and still provide humidity control .. they are most efficient at 80% ... so depending on the door leakage .. the amount of oversize is "debatable". A very tight home with proper closed cell and continuous operation can get 1T for every 1k sf. I have never done anything over 750sf per ton. But, a garage is different -- especially if you don't maintain full temp, have to open and close the door often ... and even the best doors leak.

The better units have good controls -- some of the no name brands don't do humidity control as well ... I see these at out vacation place. The Mitsubishi/Fujitsu/Daikin all work very well ... it's a question of getting a good installer.

We can fight over product and price ... In my case the Mitsubishi units checked all the boxes including the installer .. the extra $$ was not worth finding a lesser solution.

 

[yeldogt]

Yep, there is the noise factor with window units. IME, they may start out quiet when first installed, but they often get noisier as they age. This is in addition to not providing efficient heat.

I may run the mini split all year round. My buddy here has a Mitsubishi without the i-see sensor nor the hyper heat. He says that his unit has not caused a noticeable increase in his electric bill, and this is with 24/7 use.

I'll have to do more research on the hyperheat option.

You guys are great! You've brought up features I knew nothing about.

The hyper heat units have a larger outdoor unit. It's not that current systems don't work when it gets colder -- it's a question of capacity at the lower temps -- the output. The hyper heats are designed to be the heat -- they will give you full capacity down to very cold temps. No back-up is needed. Mine were humming along two years ago in sub zero weather -- virtually silent. Except the slight vibration I spoke of above. The hyper heat units also control the defrost cycle so they don't need to do it very often.

That's not to say everybody needs them -- obviously, someone in a warmer climate is not going to need the benefit of cold weather operation. My inside units have easy to clean filters.

Debating "best" or "best value" is an endless discussion. The industry is moving quickly -- the units will only get better and better. A few years ago Fujitsu was the undisputed leader .. and Sanyo owned the market prior to that. Mitsubishi made a name going after the replacement heat business with the hyper -- sometimes it's a question of liking the familiar .. knowing it will work. We were renting a place two years ago outside the city -- barn on a farm -- for the weekends .. the owner installed the best Fujitsu for the loft area. It was a fine unit -- not as quite as good as the Mitsubishi as far as controls and over all operation .. but close.

 

[Mark in Baltimore]

Thanks for the info, yeldogt. I am using this heater: http://www.homedepot.com/p/Dyna-Glo...ank-Top-Gas-Portable-Heater-TT360DG/203534107

The thing kicks **** and can warm up the garage in a jiffy. Way too hot, though, to work around in my small garage when both cars are in there.

I was using a Kero-Sun-style kerosene heater, and it just didn't put out enough BTUs.

It appears that the Mitsus have really good efficiency and are among the most quiet. I'll do more research, but I'm inclined to go with this brand.

 

[Mark in Baltimore]

The hyper heat units have a larger outdoor unit. It's not that current systems don't work when it gets colder -- it's a question of capacity at the lower temps -- the output. The hyper heats are designed to be the heat -- they will give you full capacity down to very cold temps. No back-up is needed. Mine were humming along two years ago in sub zero weather -- virtually silent. Except the slight vibration I spoke of above. The hyper heat units also control the defrost cycle so they don't need to do it very often.

That's not to say everybody needs them -- obviously, someone in a warmer climate is not going to need the benefit of cold weather operation. My inside units have easy to clean filters.

What part of the world are you located and how cold does it get?

 

[eddieK]

Hi,

Been doing lots of research here for several months as I am planning on finishing my garage. I want to add a Mitsubishi MSZ-GL12NAUI (inside unit) and MUZ-GL12NAU1 (heat pump) in my 22' L x 19' W x 9' H garage. (I'm going to have the roof deck and walls spray foamed with closed cell foam; did it to the attic and rim joist of our house and am amazed at the insulating qualities.)

• Does this unit meet the standards for the size of the garage as well as our Maryland climate?

• I have a price of $3950 installed (not including a utility rebate of $360); is $3590 a decent price?

Two contractors suggested I have a small pad built/poured so that the compressor is level. However, I have seen compressors mounted on brackets like this:

http://www.homedepot.com/p/Ductless...Conditioners-and-Heat-Pumps-BPC-3LP/205886666

$45-$75 for a bracket is much cheaper and easier than paying someone to level out the ground and make a small retaining wall for the hill next to the garage.

• Will this compressor generate too much vibration if mounted to the studs? I think it can be mounted into the poured concrete wall, but it's perhaps a bit lower than I would like (snow clearance) but better than a ground pad.

• One of the contractors said that the compressor needs to be mounted 12" away from the wall, but the mounts seem to only allow about 6" of clearance; will I be compromising the unit and/or efficiency by mounting it 6" away? I'm assuming the wall-side is the intake side, so I can't imagine that the air exchange with 6" of clearance is that big of a deal.

• Do compressors generate too much heat for my vinyl siding? I was told that the compressor needs to be about a foot away from the wall; the Home Depot one puts it 10" away which I figure is good enough.

Sorry if these are noob questions; checked the archives and only saw a few posts on this matter.

Thanks for any help!

I've mounted several of these units on those brackets...they are designed very well and the unit has a discharge side and an inlet side...with specific clearances that are met by this bracket assembly.

One of the greatest features with these mini splits is the low decibel rating...in fact Mitsubishi adopted the stealth screw design for their fan blades...similar to the screws on stealth nuclear subs.

The quote and the capacity sounds appropriate. Very little heat on the inlet side...don't worry

 

[Mark in Baltimore]

Thanks, Eddie! Interesting about the screw design.

 

[yeldogt]

What part of the world are you located and how cold does it get?

NYC -- the house is in Pa -- as was the barn.

 

[yeldogt]

Thanks for the info, yeldogt. I am using this heater: http://www.homedepot.com/p/Dyna-Glo...ank-Top-Gas-Portable-Heater-TT360DG/203534107

The thing kicks **** and can warm up the garage in a jiffy. Way too hot, though, to work around in my small garage when both cars are in there.

I was using a Kero-Sun-style kerosene heater, and it just didn't put out enough BTUs.

It appears that the Mitsus have really good efficiency and are among the most quiet. I'll do more research, but I'm inclined to go with this brand.

That heater is designed for construction or outside -- throws off lots of moisture. You should not be using in a closed space. Like putting your head in the oven.

Get a low temp Mini -- and sell that thing.

 

[Mark in Baltimore]

NYC -- the house is in Pa -- as was the barn.

Okay. So even colder temps than what I get here.

That heater is designed for construction or outside -- throws off lots of moisture. You should not be using in a closed space. Like putting your head in the oven.

Get a low temp Mini -- and sell that thing.

I know it's not ideal for inside. Garage is currently quite leaky and CO alarm has not gone off...yet.

 

[Mark in Baltimore]

If you have good (r20 or more in the walls, r40 or more in the attic) and nothing special like huge windows or uninsulated doors, 12k btu is really oversized for your space.

If you need quick recovery and dont care about comfort associated with lower relative humidity, then you will be fine.

Bringing this back to the top.

Just want to make sure I'm making the right choice. My closed cell spray foam is going to offer R-14, not R-20 or R-40. Knowing this, is the 12,000 BTU Mitsubishi going to be okay? Based on how well the closed cell keeps our attic insulated, I'd say "yes", but you guys have more experience than I do.

Lastly, the HVAC contractor I'm probably going to go with says that although the 12,000 BTU unit is fine for my needs, the 15,000 BTU would be better for a quicker recovery if I choose to, say, leave the AC off in the summer and crank it up when I need to work in it on the weekends. For the winter, I'd likely want the temps set to about 55 degrees to keep paint from freezing and to keep motors somewhat warm.

Are most of you leaving the mini split running 24/7 or are you shutting it down when not in use for an extended period?

Thanks for any input!

 

[PoorOwner]

Bringing this back to the top.

Just want to make sure I'm making the right choice. My closed cell spray foam is going to offer R-14, not R-20 or R-40. Knowing this, is the 12,000 BTU Mitsubishi going to be okay? Based on how well the closed cell keeps our attic insulated, I'd say "yes", but you guys have more experience than I do.

Lastly, the HVAC contractor I'm probably going to go with says that although the 12,000 BTU unit is fine for my needs, the 15,000 BTU would be better for a quicker recovery if I choose to, say, leave the AC off in the summer and crank it up when I need to work in it on the weekends. For the winter, I'd likely want the temps set to about 55 degrees to keep paint from freezing and to keep motors somewhat warm.

Are most of you leaving the mini split running 24/7 or are you shutting it down when not in use for an extended period?

Thanks for any input!

I recently picked out a Mitsubishi also but didn't oversize. I resisted the temptation. I know well ahead when I will need to spend a day in the garage so I would just turn it on the night before to reduce humidity and pull down. But I won't have instant relief if don't plan ahead. The smaller unit really just sips electricity. Bigger unit have bigger lines and compressor and is less efficient even if they throttle.

Why I picked Mitsubishi. The non hyper heat model still gives better heat capacity than the competition. They also lets you run cooling down to something like freezing outside. (For example server rooms). My previous system says not to use it when under 60 outside. And actually did not feel cool enough inside when the outside temp drops but the garage is obviously hotter. Apparently need some ambient heat on the outside unit in order to cool better.
Only the top 3 brands makes me feel confident about have parts down the road should I need to repair it. The other stuff from Amazon etc is basically a throw away system.

What kind of warranty are you getting since it sounds like the contractor is a dealer? I am going through internet order and having a licensed tech install it. They told me 5 years but Mitsubishi seems to states registered unit gets 10 years.

 

[yeldogt]

If we open the windows -- we turn them off ...otherwise they are "on" .. we turn them up when we leave for any extended period. What thickness are they spraying?

The key with foam is its ability to seal everything up -- I did a 2" foam and batt project about 10 years ago .... after the 2" of foam was applied the single story addition was comfortable with just the AC pass through from the main house. The batt's did little .. but I had to do them for the code.

Personally -- I would get the extra capacity. The sizing of the equipment is a bit different with Mini splits. They run most efficiently up to around 80% ... you don't want to have a situation where sizing it would have it running 90% all the time. That's why it's important to do a good heat and cool load on the building. My guy used an average temp -- and then looked at the extremes and how that fit with the 80%

In many cases conventional AC units (single speed) get oversized because the installers use outside temps in the calculation that are very rare .. you don't size an AC for 70 degrees inside when it 105 outside if it only hits that once every 10 years and you always keep the house at 72.

With a mini -- you can push the sizing up a bit. In my new build the kitchen's AC load is about 12k -- the heat is a bit more. We are going to install a 18k head. System for this area of the house is a three head Mitsubishi hyper heat. I want the extra capacity for when we have parties and the large stove. I did this in another project and it has worked out well.

I think for a garage having that extra capacity will be useful.

The 80% also helps in areas where the heating and cooling load is not equal. The reason the hyper heats are great -- they give you that full capacity down below zero. It's not that other mini splits can't work in lower temps -- it's they don't give the full capacity at zero degrees. You have to make sure you have what the building is going to require .. I don't care if the unit is running flat out for a couple of days on the few days it's zero -- but it's got to have the capacity needed.

 

[Fueler]

Mine runs 24/7 except when the temp and humidity is nice. Then it is off.
Doesn't happen often.

 

[Mark in Baltimore]

I recently picked out a Mitsubishi also but didn't oversize. I resisted the temptation. I know well ahead when I will need to spend a day in the garage so I would just turn it on the night before to reduce humidity and pull down. But I won't have instant relief if don't plan ahead. The smaller unit really just sips electricity. Bigger unit have bigger lines and compressor and is less efficient even if they throttle.

Why I picked Mitsubishi. The non hyper heat model still gives better heat capacity than the competition. They also lets you run cooling down to something like freezing outside. (For example server rooms). My previous system says not to use it when under 60 outside. And actually did not feel cool enough inside when the outside temp drops but the garage is obviously hotter. Apparently need some ambient heat on the outside unit in order to cool better.
Only the top 3 brands makes me feel confident about have parts down the road should I need to repair it. The other stuff from Amazon etc is basically a throw away system.

What kind of warranty are you getting since it sounds like the contractor is a dealer? I am going through internet order and having a licensed tech install it. They told me 5 years but Mitsubishi seems to states registered unit gets 10 years.

Thanks for the info on your experiences. So, I believe a vote for the smaller, 12,000 BTU unit.

I believe I'll have a 12 year parts warranty since the guy is a Diamond dealer.

If we open the windows -- we turn them off ...otherwise they are "on" .. we turn them up when we leave for any extended period. What thickness are they spraying?

The key with foam is its ability to seal everything up -- I did a 2" foam and batt project about 10 years ago .... after the 2" of foam was applied the single story addition was comfortable with just the AC pass through from the main house. The batt's did little .. but I had to do them for the code.

Personally -- I would get the extra capacity. The sizing of the equipment is a bit different with Mini splits. They run most efficiently up to around 80% ... you don't want to have a situation where sizing it would have it running 90% all the time. That's why it's important to do a good heat and cool load on the building. My guy used an average temp -- and then looked at the extremes and how that fit with the 80%

In many cases conventional AC units (single speed) get oversized because the installers use outside temps in the calculation that are very rare .. you don't size an AC for 70 degrees inside when it 105 outside if it only hits that once every 10 years and you always keep the house at 72.

With a mini -- you can push the sizing up a bit. In my new build the kitchen's AC load is about 12k -- the heat is a bit more. We are going to install a 18k head. System for this area of the house is a three head Mitsubishi hyper heat. I want the extra capacity for when we have parties and the large stove. I did this in another project and it has worked out well.

I think for a garage having that extra capacity will be useful.

The 80% also helps in areas where the heating and cooling load is not equal. The reason the hyper heats are great -- they give you that full capacity down below zero. It's not that other mini splits can't work in lower temps -- it's they don't give the full capacity at zero degrees. You have to make sure you have what the building is going to require .. I don't care if the unit is running flat out for a couple of days on the few days it's zero -- but it's got to have the capacity needed.

The guy ran the numbers and was the only contractor to do so. He thought the 12,000 BTU one would be more than fine as long as my garage door isn't leaky. But he did say that the 15,000 BTU unit would be better if I left it off for a good period and could heat and cool quicker than the 12,000.

Spray foam depth is 2" and is limited by the depth of the 2x4 studs to achieve R-14.

Mine runs 24/7 except when the temp and humidity is nice. Then it is off.
Doesn't happen often.

What are your BTUs and how big is your space? Insulation?

 

[bzinsky]

Do not mount it 6" away from the wall. I was considering wall mount for a project but ended up roof mounting. After several times of working on the roof and seeing them run, I would highly advise not to mount closer to the wall than recommended.

There's way more airflow than you would expect, and it's a vastly different temperature than ambient. Whatever you do, you do not want to impede with the airflow nor do you want the unit sucking in any of it's own exhaust.

Also the exhaust will be blowing away from your structure, not towards it, so no worries about melting any siding even if it was hot enough to do so.

 

[bzinsky]

Also you don't need a hyper heat in Maryland, especially for your application.

A) Not that cold, here in NJ, where I'm sure it's slightly colder than Maryland, we haven't hit 0 degrees in a long time. I was surprised by that when I looked it up. With the wind chill yes, but not ambient. There are very few days out of the year that are single digits. Most of the winter hovers around 20-25 degrees. When mitsu designed the hyper heat, I'm pretty sure they had climates like southern canada on their radar. Hell when I bought my top tier LG units, which aren't rated as low as the hyper heats, they weren't even listed on the US website but were front page of the canadian LG site.

b)You have backup heat. If it was your only heat source, low temp output is very important since those 2-3 days a year that have the highest requirement for heat and your air source heat pump is at it's lowest output. It only happens a couple times a year in our climate that would start to stress a less expensive unit.

c)it's a garage, it's not a critical heating application and by not maintaining room temp all year round like you would in a living space application, you're not really taking advantage of the hyper heats efficiency.

I know the hyper heats are expensive, I just think for your application I would go with a less expensive mitsu.

 

[Mark in Baltimore]

Do not mount it 6" away from the wall. I was considering wall mount for a project but ended up roof mounting. After several times of working on the roof and seeing them run, I would highly advise not to mount closer to the wall than recommended.

There's way more airflow than you would expect, and it's a vastly different temperature than ambient. Whatever you do, you do not want to impede with the airflow nor do you want the unit sucking in any of it's own exhaust.

Also the exhaust will be blowing away from your structure, not towards it, so no worries about melting any siding even if it was hot enough to do so.

Also you don't need a hyper heat in Maryland, especially for your application.

A) Not that cold, here in NJ, where I'm sure it's slightly colder than Maryland, we haven't hit 0 degrees in a long time. I was surprised by that when I looked it up. With the wind chill yes, but not ambient. There are very few days out of the year that are single digits. Most of the winter hovers around 20-25 degrees. When mitsu designed the hyper heat, I'm pretty sure they had climates like southern canada on their radar. Hell when I bought my top tier LG units, which aren't rated as low as the hyper heats, they weren't even listed on the US website but were front page of the canadian LG site.

b)You have backup heat. If it was your only heat source, low temp output is very important since those 2-3 days a year that have the highest requirement for heat and your air source heat pump is at it's lowest output. It only happens a couple times a year in our climate that would start to stress a less expensive unit.

c)it's a garage, it's not a critical heating application and by not maintaining room temp all year round like you would in a living space application, you're not really taking advantage of the hyper heats efficiency.

I know the hyper heats are expensive, I just think for your application I would go with a less expensive mitsu.

Thanks for the good points, and sorry for the delay in responding!

I don't have a better place to mount the compressor other than on a bracket. I could mount it on the ground, but then I have to worry about snow blocking the airflow or have to build a roof for it. My contractor said that the brackets are fine.

The hyper heat is only an extra $300, nominal amount, IMO. I hear you with regard to the temps here in Maryland and was on the fence about the hyper heat. I figure it's better to get it. I don't plan on using the propane heat at all.

The more I think about it as well as how well-insulated I think the spray foam will be, the more inclined I am to leave the winter temps at about 50 degrees and the summer temps at about 77 degrees.

Can I obtain any other opinions on whether the 12,000 BTU unit will be adequate with this type of use? My gut says yes, but this is well outside of the scope of my expertise.

Thanks!

 

[bzinsky]

yes the 12k hyper heat would definitely cut it, if it doesn't you have some serious insulation leaks

I use 9k units in a building with 20 apartments. one unit per apartment. Apartment sizes range from 450-600sq ft, they have less insulation than your garage and they have no problem heating or cooling.

Make sure the installer does the install correctly, many don't use a micron gauge or vacuum it down enough. I'm pretty confident it has a large impact on efficiency and output, and the hvac guy might not think so because every time he installs one it "works fine."

 

[MushCreek]

We've been using the Mits HyperHeat units for our house in SC. A 12K does the whole house (1400 sq ft), but the house is very tight and well insulated. We have a 9K unit in the master suite, but don't really need it. It is virtually silent, inside and out. I mounted them on wall brackets, about 3 feet off of the ground. They are about 6 inches from the wall, and it doesn't seem to hurt anything.

Power bills only add about $20/month during A/C season, and $40/month during heating season. We go for long stretches with neither, so we only spend about $200 a year on HVAC. We use to spend that in a month in our old house!

I bought two units, a 12K and a 9K online. Total, with brackets and refrigerant lines was $3400. I installed them myself, and paid a contractor $600 for the final commissioning, so I'm at $4K for two units.

We run ours 24/7 during the season. I get the feeling that recovery would be slow if we let the house get really hot or cold. Our house is concrete, so there are 100 tons of concrete in the walls to bring along. I think 12K is plenty for your space, and there's not much harm in oversizing a mini as opposed to a traditional system.

 

[Mark in Baltimore]

Solid info! Thanks! Will go with the 12000 BTU unit. Seems like it will be fine especially after I spray foam.

 

[walrus]

There are thousands of mini splits mounted on wall brackets