Mini split sizing

[sharpie_101]

Looking at cooling my attached 3 car garage.

650 sq ft, cinder block walls, insulated garage doors. The side walls are exterior walls and the back wall is 1/3 exterior (block), 2/3 shared with house. Some insulation on the roof as the second story somewhat overlaps it.

Location is south Florida, which equals hot and very humid.

I will be buying a Mr. Cool from Costco and doing the install myself except for the electrical part.

18k btu or 24k btu?

 

[SALIV8]

I'm a diy'er and have no basis for this whatsoever except me shooting from the hip.

With that said I'd probably get the 24- based on what it can modulate down to, in the hopes of taking advantage of the inverter as I wouldn't be too worried about oversizing it a bit.

 

[sharpie_101]

Thanks for the input!

What do you mean by the inverter? Are you referring to the variable speed feature?

 

[Jazzman442]

I think you will need a much larger unit. I live in Central Florida on the west coast. I have a 1000 sft Garage with 12' Ceilings. Insulated doors with a radiant barrier under roof. I had a 12k btu ac it didn't even get the area where my bench is cool. As soon as you open a door al of the heat and humility will rush in. Post how it works I am having mine estimated next month.

 

[PoorOwner]

The 24k modulate down to only 12k if I recall. So not exactly low output.
These particular units have a rather traditional hysteresis so they over cool it and then shut off the compressor for a while until it shoot a bit over again. So it will feel humid for a while. What that means is that it is better not to oversized them. Just my opinion.

 

[TangoFoxTrot]

I would go big for a garage, it's just a much different application.

It's usually not running all the time 24/7 at like 75 degrees like you would for a living space. When you're in there working in the summer, you usually want it as cold as possible and for the temperature to drop as quickly as possible. Plus there's all sorts of insulation issues that garages have, it's just usually not as tight as a home.

I had a garage that the previous owner installed a traditional split system (not a minisplit) and I when I worked out there, I basically set it as cold as it would get and I always wanted it colder.

 

[SALIV8]

Thanks for the input!

What do you mean by the inverter? Are you referring to the variable speed feature?

Correct, the compressor can ramp down or up based on load and that helps a ton with energy savings.

 

[Falcon67]

My hip shot would be 15~18K here for that sq/ft - but in FL or Houston, most any Gulf area 24K. It's going to spend time wringing out the air. If you don't/haven't lived near the Gulf you don't really have a feel for how much humidity is constant in the air. People make a living pulling big plastic tanks around on trailers and blasting moss, misc green growth and pine junk off driveways and houses.

 

[Stuart in MN]

You need to do a heat load calculation in order to have any idea of what size unit you need...if you don't have that done by a professional check around online, there are a number of online calculators out there. I would recommend running the numbers through more than one calculator, to make sure you get reasonably consistent results.

 

[finn]

You can probably get away with an oversized unit in the desert, but not in a humid climate like South Florida.

If it’s not running, it’s not dehumidifying. You want it to be running just short of constantly, in my opinion. At least for me, I can deal better with a higher temperature better than higher humidity.

 

[Ohmthis]

You need to do a heat load calculation in order to have any idea of what size unit you need...if you don't have that done by a professional check around online, there are a number of online calculators out there. I would recommend running the numbers through more than one calculator, to make sure you get reasonably consistent results.

While I agree a load calculation is important, a garage isn’t really where manual J calculations are used. A garage is very similar to a commercial building where a manual N is used. Although it isn’t really that either. For a one man shop, use a manual J and see where it falls, use a size smaller in the range (Ex. The calculation shows 13,500 btu heat gain, use a 12k over a 15k unit. It will run for longer times and help dehumidify the area better.) It may not fit ALL the criteria, but it will be better than a bunch of people guessing. You can look in your area and see if there are groups that do load calculations and pay the fee. Though since this is going to be a DIY project, I doubt you have figured money for that. Hope this helps.

 

[yeldogt]

The ceiling insulation is really going to matter ... it's very hard to give any advise when the insulation is not known.

As above -- do a simple cooling load calculation. You need to figure out where to start ....

Also with any amount of humidity you will want to run it longer ....

 

[Jackfre]

Do you intend other building modifications? If so, take that into consideration in the choice of equipment. Don't buy to large and make it larger by insulating. Better if you plan the final building set-up and buy for that building. You can reduce load with insulation, etc. If this will be an on/off type set-up and you want rapid cool down I'd go with a 24.

 

[B-Well]

Call the team at Ingram's Water and Air Equipment. IWAE.com They were extremely helpful. We discussed sizing requirements and ensured I did not Oversize and short cycle my unit shortening the life of the unit and increasing energy consumption. I was also able to get a NEW, scratch and dent compressor for half off with only cosmetic damage and covered by the same full warranty. I have 722sqft with 13' ceiling and an 18k Mr Cool Oasis system. It is 84 outside and 64 inside. Our energy bill did not change much. maybe 5%

 

[SALIV8]

Im curious, since the indoor units have fan speed controls as slow as low, that will keep it running to maintain temp setpoint if it is slightly oversized and humidity is higher than one would like.

Not to mention most units have a specific dehumidication setting. Slightly oversizing minis help to keep the system in the vfd range and thus produce more savings based on ramping down of compressors.

If it is slightly undersized, the compressor will run at full tilt and thus you will see no energy savings.

 

[Wileel]

I have a similar sized shop in the North FL Panhandle, but mine is stick built. When I remodeled I took down the OSB walls and insulated with batts, put up drywall and installed a Mr. Cool 24k DIY. The ceiling currently has no insulation and the two garage doors are not insulated either however, that will change once I fix or replace the ceiling sheetrock (thanks hurricane Michael). This unit has had no problem dropping the humidity and temps into the mid 70's inside during the peak on summer and also has been sweet to warm it up to the same in the winters. I struggled with the same question if I should oversize the unit and I'm glad I did. It runs hard at first but after maybe 30 min it throttles down and maintains temp nicely.

 

[sharpie_101]

The ceiling insulation is really going to matter ... it's very hard to give any advise when the insulation is not known.

As above -- do a simple cooling load calculation. You need to figure out where to start ....

Also with any amount of humidity you will want to run it longer ....

The side with the double garage door has 16" of blown insulation on top, plus most of it has the second story up there. The right side, or 1/3 has zero insulation on the roof.

I have a similar sized shop in the North FL Panhandle, but mine is stick built. When I remodeled I took down the OSB walls and insulated with batts, put up drywall and installed a Mr. Cool 24k DIY. The ceiling currently has no insulation and the two garage doors are not insulated either however, that will change once I fix or replace the ceiling sheetrock (thanks hurricane Michael). This unit has had no problem dropping the humidity and temps into the mid 70's inside during the peak on summer and also has been sweet to warm it up to the same in the winters. I struggled with the same question if I should oversize the unit and I'm glad I did. It runs hard at first but after maybe 30 min it throttles down and maintains temp nicely.

I think I made up my mind and will order the 24k BTU. I know most of you will disagree with my choice, but I am not planning on running this 24/7, I just want AC for when I work in there. I am not trying to control how humid it is, just be able to get it down to 75 or so during the summer while I am in there.

 

[sharpie_101]

If this will be an on/off type set-up and you want rapid cool down I'd go with a 24.

This is exactly what I want. I want to get home from work at 5:30 and be able to turn it on and get to work on my car in an hour or so. If it can be controlled remotely, like the Mr Cool says it is, I can even turn it on from work and have it ready by the time I get home.

Once I am done working in the garage, I can shut it off.

I really appreciate all the responses, I came in here thinking I would order the 18k BTU and be done, but the more I thought about it this past week I will order the 24k just in case.

Thanks again!

 

[Erocktampa]

This is exactly what I want. I want to get home from work at 5:30 and be able to turn it on and get to work on my car in an hour or so. If it can be controlled remotely, like the Mr Cool says it is, I can even turn it on from work and have it ready by the time I get home.

Once I am done working in the garage, I can shut it off.

I really appreciate all the responses, I came in here thinking I would order the 18k BTU and be done, but the more I thought about it this past week I will order the 24k just in case.

Thanks again!

How did this workout? Working on getting one in Tampa and was thinking of Getting double split for my 880 sq ft garage.

 

[FL Guy]

How did this workout? Working on getting one in Tampa and was thinking of Getting double split for my 880 sq ft garage.

I’m just north of you, 2 hours. Garage is 900sf and I have a 36k Btu unit. I love how fast the temperature recoups when a garage door gets opened.

 

[Erocktampa]

I’m just north of you, 2 hours. Garage is 900sf and I have a 36k Btu unit. I love how fast the temperature recoups when a garage door gets opened.

Thanks for update! I'll have to go at least 24k unless the price isn't much different. Did you do a double mini split? It going well during these summer months?

 

[FL Guy]

Thanks for update! I'll have to go at least 24k unless the price isn't much different. Did you do a double mini split? It going well during these summer months?

Just a single head unit. It’s doing great !