Shop AC

I have an un-insulated 640 SF garage/shop. It has open stud walls and rafters. The walls are currently clad with Peg Board.

I am considering installing a window or through wall AC with supplemental heat to provide temporary cooling and heat while I am in the shop and working. I don't expect it to feel like my living room out there. It gets up in the high 90's for about 3 months and even with doors and windows open and fans running, its not a real pleasant place be. I am just looking for some cool air blowing on me, maybe supplemented with some fans to move the temperature 10 to maybe 20 degrees to create a more comfortable working environment. The heat would only be used intermittently during a few cold winter days to keep the temp in the shop above freezing, and to knock the cold edge off when working after a cold front. 6 months of the year I won't need anything but open doors. This wouldn't be for 24/7 climate control, just mostly used during the time I am out there in the evenings or on weekends, during the few months when it is needed.

I know that it would be better to insulate, but I have future plans to renovate and will address that at that time. I am just looking for an interim solution for cool air. It is too humid here to use the evaporative type of coolers and I don't like the thought of all that additional moisture in the air.

I am looking at the window units sold at HD and LOWES. They both have a similar selection. I am limited in power for this effort to either 20 amp 115V circuit or a 20 amp 230V circuit. There looks like Lowes/HD have a 230V 18 ton unit that draws 7.3 amps cooling and 16 amps heating. This unit is rated for a 1050 sf area.

18 tons is more than what is needed for this footprint, but given the lack of insulation and open rafters, I am thinking the larger unit may be a better choice. Otherwise, I think it may size to a 12 to 14 ton unit.

I am wondering if anyone has done anything similar and if this worth pursuing. I can accept an increase in the electric bill and don't mind the +/- $500 investment in the unit.

Thanks for your help.

Edited: Please insert BTU's where tons is mentioned above!

Brad
I put a Kenmore 24,000 BTU in my shop
My shop is 9720 cubic feet
It is well insulated and I put a wall right through the middle of it for the machine shop 16'x 26' , the other half is the bigger half is 2o' x 26'
You can hang meat in that machine shop
If I was you I would get the biggest one I had power to run .
 
I have a mini-split in my shop and love it. It has heating, cooling and drying modes so it works as a dehumidifier too. I use heat in winter but don't keep it all that warm, and can warm it up in an hour or so when I plan to work out there (extra capacity and its "powerful heating mode" is nice for that). In summer I use drying mode to keep the shop at 45% humidity for making guitars and the tools love the dry air too. Drying mode also keeps it cool but it's regulated by humidity not temperature. It runs on a 20A 240V circuit.
 
I am not too far from you in Friendswood. My shop is @900 sqft. Only the attic is insulated. Several years ago I put in an 18000 btu unit. It does a pretty good job. When it comes time to replace this unit, I will probably go with a 24000 unit. On days like today, it has a hard time keeping up. But it sure does make life in the shop more tolerable in the summer

Randy
 
Counter-intuitively, I think larger capacity can be much more economical. It costs a little more up front but if you have enough capacity to bring the shop to a comfortable temp in an hour or so, then you're more likely to set the thermostat cooler in winter and warmer in summer, and just give it a boost when you'll be out there. If the unit can barely keep up then you have to leave it set at desired temp all the time. I just took the manufacturer's recommendation and then went up a size.
 
I had a mini split system installed in my 900 sq ft shop (garage) that had no insulation in the walls or the ceiling. While it did work, a few weeks later I decided to see if I could get insulation blown into the sheetrock covered walls without removing the sheetrock, and it not only turned out to be possible but was easier and less expensive than I had expected. While they were here I also had insulation blown into the ceiling, and the results have been great. On a 95 degree day I can start the A/C and within 30 min the shop is much drier and quickly becomes comfortable to work in -- Mine is on a 230 volt 20 amp circuit Good luck with yours -- Jack
 
Brad, If you can swing it, insulation will make it much more comfortable and economically easier.
I have a 30x40 metal shop--t was almost unbearable to work in in the summer(and winter). I hung the vinyl faced insulation in the ceiling and walls and it made such a difference!! I then got used to having comfort and wanted more so I built a room inside 11x40 with 8" ceiling (insulated) and installed a 24,000 btu AC in one of the windows. It's really nice to work in 75* when it's 95* outside with 70-80% humidity or 30-40* in the winter.

Getting old does have some perks! And I can't take it with me so might as well enjoy it now.
 
Jay, there is a drawback to oversizing your AC. If it cools the air too quickly and shuts down, less humidity is drawn from the air, so yes you have colder, but wetter air than usually desired. The ideal sizing runs long enough (but not too long) to cool the air and dehumidify it to a comfortable level.
 
Good insulation is always required before heating or air conditioning a space, unless you are the type who likes to light paper money on fire... Insulation pays for itself quickly with both comfort and cost savings.
 
Jay, there is a drawback to oversizing your AC. If it cools the air too quickly and shuts down, less humidity is drawn from the air, so yes you have colder, but wetter air than usually desired. The ideal sizing runs long enough (but not too long) to cool the air and dehumidify it to a comfortable level.
That's true for a constant-speed system, as many are, but my mini-split has a variable-speed compressor so it adjusts it own power level and I presume its software tries to optimize energy efficiency. I've never heard it run at full speed except when I use its temporary "powerful" mode to warm things up quickly in the winter. In summer I use only drying mode, which also cools enough to stay comfortable in my Michigan climate, but presumably is optimized for efficient moisture removal.
 
Counter-intuitively, I think larger capacity can be much more economical. It costs a little more up front but if you have enough capacity to bring the shop to a comfortable temp in an hour or so, then you're more likely to set the thermostat cooler in winter and warmer in summer, and just give it a boost when you'll be out there. If the unit can barely keep up then you have to leave it set at desired temp all the time. I just took the manufacturer's recommendation and then went up a size.
When I bought my AC unit I sent my son and his
Friend to Sears with my credit card . They was setting up a pool table in the split side of my shop.
Which is now my Machine shop Toolroom .
He said it is to hot in the game room for them to
Enjoy hanging out . I told him to go get a Kenmore
AC At Sears . About 45 mins. Later he called me
And said they have a 18,000 BTU 240 volts ,
I said what else do they have - he said a 20,000 BTU
And they have a 24,000 BTU all run on 240 Volts
The 24,000 was the largest one that they have
I told him to get that one get the biggest one .
And I never have regretted it ether .
 
Back
Top