What's new
What's new

New shop split unit ductless BTU calculation?

henrya

Titanium
Joined
Jun 25, 2008
Location
TN
Moving to new shop. Lathe, mill and handwork. 20 X 20 with 12 foot ceiling. Well insulated.

I can put a ductless unit through the wall. The various online calculators tell me about 18,000 BTUs. Does this sound right? I am ignorant in this field and would like to get it right the first try.

Any comments or advice based on your experience about this kind of installation are welcome. Brands you like or don’t like would be good information too.

Thank you in advance.
 
two large window ac units could provide (theoretically) 24,000 btu cooling and might only cost you a couple hundred bucks depending on what's on Craigslist in your area.

a minisplit of twice the eer would cost you on the order of $1000 per ton and on the order of a days' labor for an hvac tech to vac it down and hook it up. it would take several years or even an entire decade for the increased efficiency to pay for itself.

if you are committed to your space for a long time and if it is indeed well insulated with only a few machines running sometimes.. than a 1 ton mini-split can probably handle your whole space. you can buy one off ebay for $500 bucks and install it yourself by simply venting a small amount of the refrigerant to wash the air out of the indoor unit when you go to hook up the flare fittings. (no, i'm not making that up lol, you don't need a vacuum pump, its all explained in hieroglyphics in the instruction manual )

or pay a legit installer to install a high efficiency 1 or 2 ton unit for >$2,000.
 
If you do a ductless the only thing going through the wall is the copper and drain. about 1 ton per 500 sq. is a rough guesstimator. I did a 1 ton unit for my garage and it blows cold air but not having the roof sheetrocked and insulated lets he right back in fast, guess i know this winters project is. i did the mr cool wall mount, wishing i did the square style you can mount in the center of the room.
the line set were pre-made lines that were tighten down, vacuum and go. but, the sets are premade so make sure everything reaches with the included set or your going to have to have another one ordered. There are some line sets that do have a pre charge in them so it's just tighten down and go. but if you get the line set that needs to be vacuumed a a/c guy can do that in less then an hour.
 
I oversized the two split units I have in my house. This way I do not have to listen to them run at high speeds. Consider paying a little extra to get heat pump action as well. They make a ceiling cassette that mounts flush into the ceiling. But it is hard to get to to clean the filter.
Bill D.

PS: Freidrich makes the quietest indoor units. Others can be twice as loud at low speed. Most are at least 50% louder. If they do give the indoor Db number do not buy the unit, it will be too loud.
 
I bought the cheapest shit 120V mini split on Amazon for our R19 insulated 14x36 office. I installed it myself (I did use a vacuum pump) and it's been going non stop for 2 years heating in the winter and cooling in the summer. It will freeze your ass out of there on a 110 degree day if you set it to 65 and has worked fine for heat down into the coldest 15 degree or so nights we get here in the Northwest.
 
I have a 25000 btu split unit in a 18 x 30 shop. no problems since install 10 years ago. place the unit so you can reach it with a ladder, twice a year open up and clean the air filter. The coldest has been 9 below zero F, kept the shop at 74 just fine. I have high E windows, 6 in walls and a foot on insulation in the ceiling.
There is no other heat source. Cost about 5K ten years ago, unit is a Fujitsu. The shop has three outside walls.
 
If you are sizing for AC consider the amount of heat you are generating.

I used to run a 2 ton wall unit in a modestly insulated 1000 sq ft building and it did not cut it on the hottest days, but was better than nothing.
Ceiling height is big, higher ceiling lets the heat rise.

If it is just you, I think the size is ok.

For a house I advise against oversizing as most calculators oversize to start, and a larger unit will have difficulty maintaining temp properly when it is near its lower limits, which is most of the time
 
Just installed three of them in my house including a 24,000 BTU unit in my garage/shop. It's a two car garage, 20 x 20 roughly with 8 foot ceiling. No insulation in the walls or ceiling. First day last month, 100 degrees outside, inside around 73 degrees. You could almost hang meat in the garage. It replaced a so-called window duct unit that was supposed to be a 13,000 BTU unit. It could not keep the garage under 85 on a 100 degree day, and included help from the house. Had a $620 electric bill for July, this months bill with about two weeks of usage is $450. Won't know how the other two mini-splits will fare on the electric bill, I'm shooting for something under $400! I probably could have installed a 18,000 BTU unit and been just fine. We are talking about moving it to the living area of the house and installing a 18,000 BTU unit in the shop next year.

The mini-splits are very high efficient and will put window units to shame. I highly recommend them. I'm glad I got them. My son and I determine we will have our money back in about 14-18 months, We intend to insulate the ceiling of the garage and other parts of the attic that needs more insulation. Right now is not a good time to do it. Ken
 
I have a 24x27 shop with 12+ ceilings, insulated on all six faces, and it stays 68F all year round with a Mitsubishi Mr.Slim outside unit (either 12K or 18K BTU, don't recall and not at shop to look right now) and one ceiling cassette.
 
I put a single 1.5 HP LG Split in my rental houses over here and you could almost hang meat.
15' X 30' with 8' ceilings. hollow block houses, no insulation, single pain windows, no weather stripping and outside temp rarely gets under 90 degrees year round. Price per Kwh is $.22 cents and even with the air running 18 hours a day the power bill has never topped $80 even with all the other usages.

I chose the LG because of the dual inverters efficiency factor was much higher than most of the other brands and dual inverter handles dirty power and spikes really well.
 
Greetings, it is I, Steelballs…..

It'll be the best investment you could possibly make. I have a Samsung Smart Inverter ductless in my house and it is truly awesome, heats very well in the fall also.

Next year I'll be putting one in my 25' X 35' shop with 12' ceilings, and that'll be a 24k btu unit, most likely a Fujitsu.

Seems like quite a few guys install the MRCOOL minisplits because their supposedly truly DIY. The line sets are precharged which makes it DIY I guess. Not a brand I would consider but I've read positive reviews on them.
 
BTUs are BTUs, weather it is a split unit or a window one. I am in south Texas, near the Gulf, and have a similar sized shop, aroung 22' x 22' with an 8' ceiling and a storage room, about 8' x 20' off one corner. My water heater is in the storage room so that adds some heat. It is partially insulated on the northern exterior wall. The west wall is almost all garage doors so not much room for insulation there, but if I replace them I will get insulated ones. The other two sides are common to the house. The ceiling is not insulated.

The thing about those on-line calculators is that they are for the average, living space in an average house. They do not take in all the factors. In my case, I tried 10,000 BTU and then 18,000 BTU units but both were somewhat lacking in the heat of a south Texas summer and for the extra heat load of the water heater and the machines being run in the shop. You must remember that any electric usage in the shop WILL become heat: 100% of it ultimately becomes heat unless it manages to escape out of a window or door. But here, in summer far more heat will come in those openings than what can manage to escape so 100% of that electric usage is a realistic and practical figure. And this adds to the amount of AC BTUs that you will need. Of course, in the winter it subtracts from the heat needed.

I presently have my second 22,000 or 24,000 BTU window unit. Both of them cooled the shop well, even in the summer. Both had heater coils that were sufficient for the winters here; I don't know about Tennessee. You may find that 18,000 BTUs are not enough on the hottest summer days. Or it may be.

My prior unit was a Frederich and the present one is a GE. Both of them are relatively quiet. In case you are curious, the Frederich failed due to clumsy maintenance on my part. I hope not to repeat that mistake.
 
Moving to new shop. Lathe, mill and handwork. 20 X 20 with 12 foot ceiling. Well insulated.

I can put a ductless unit through the wall. The various online calculators tell me about 18,000 BTUs. Does this sound right? I am ignorant in this field and would like to get it right the first try.

Any comments or advice based on your experience about this kind of installation are welcome. Brands you like or don’t like would be good information too.

Thank you in advance.

This is strictly anecdotal, I don’t have any background in AC. I just built a 30x40 shop, 12 ft eve height, 4:1 slope roof, open cell spray foam insulation on ceiling and walls, insulated roll up door, steel building.

I put in two Mr. Cool 24K units. I think it was probably too much. But I’d rather overdo it. That being said I know you don’t typically want to oversize an AC unit. That’s why I put in two separate units. On the hottest days here in the Houston summers one unit can keep up if I set the temp to 78. When I’m out here working however I set the temp to 71. I need both units running to keep up with that temp. But when I’m not in the shop I set it to 78 and leave one unit running. The theory is that over sizing keeps the units from cycling on enough to control the humidity. I have 4 humidity sensors around the shop and manage to keep the humidity at 46%.

As one of the other posters mentioned the Mr. Cool units are made for DIY. I had an AC company come out to quote me a mini split system. They were the ones that did the calculations and recommended 2 x 24K units. They were going to put in Mitsubishi units and quoted me about $8K. I put in the Mr. Cool units myself for $3K.

My suggestion, get an AC company to come out and quote you and let them do the calculations. Even if it costs you $100 for a service call to do so it’s probably worth it to be confident of the requirements.


Sent from my iPad using Tapatalk
 
As I said I oversized my home units. But in my climate I do not worry about removing humidity in summer. If folks in your area use swamp coolers humidity is not a concern. Lots of swamp coolers here. In summe rany humidity over 35-40% is feeling swampy to us.
Bil lD
 








 
Back
Top