What Size of Window Unit A/C for Shop?

My shop is 32 x 48--1,536 square ft. It has 14 ft side walls and is insulated well. Just built it last year. I have been told I should just put a window unit in there and it will be much more comfortable this summer. What size of window unit do you recommend? Looks like a 12,000 btu is one of the larger models. Thanks

From my past use of them, your need is going to be double that. Too small of unit MAY sort of cool you, but in the long run it will just cost more electricity and you will later wish you had spent the 100 bucks more for the bigger unit. Here is an example of the size you should be getting. https://www.acwholesalers.com/LG/LW2412ER-24000-BTU-9-4-EER-Window-Air-Conditioner-230V/29614.ac

Steve

General rule of thumb is 400 sq ft per ton of cooling. A ton is 12,000 BTU/hr, so you'd need 4 of those units. While you can buy larger units, you'd be better off with something like 4 12's as opposed to a pair of 24's, due to the fact that a couple larger units will have trouble throwing the air far enough to give even temperatures. 12's will normally run on a 120V circuit, while the larger ones will require a 240V circuit, which can cost more to add than the unit itself costs.

I think you'd find a single 12 won't do much for you, but you could start out with a couple 12's if you didn't want to go all in at once. If I was installing 2 12's, I'd attempt to locate them at quarter points along the 48 ft wall if possible. IOW, put one unit about 12 ft in from the end wall at each end of the building.

While this wouldn't be enough to hold the shop at 72* on a 90* day, it will be enough to make a big dent in the humidity level as well as lowering the temperature to a tolerable level. Humidity is the main factor in a shop being uncomfortable, and its surprising how comfortable even 80* can be when the humidity is low.

One other factor is the type machines you're running, and whether you're evaporating a lot of coolant in the cutting process. For example, if you run a single 15hp VMC at full load, all the electricity that goes into the machine ultimately ends up as heat, either sensible in the form of raising the air temperature, or latent in the form of evaporating coolant and raising the humidity in the space. If you assumed an average continuous spindle and accessory load of 10hp, or about 7.5kW, it would take a little more than 2 tons of cooling just to offset the heat produced by the machine.

All said and done, window units won't give you the best cooling system, but they will be your cheapest option by far. And, you can add them incrementally to the point where the shop is comfortable to suit yourself.

My shop is 1400 sq. ft. I installed a 24k BTU and it works very well. I am well insulated with 16 inches of insulation blown in the ceiling. I do have to run a fan to get the other side of the shop as cool as it is by the unit though. The main problem is when I have to do some welding I loose it all to get enough ventilation.

I'd look into a mini split system, small hole through wall and way better SEER rating on most all of them compared to the window units which means less money to run.

i have a 24,000 btu 220v unit in my shop main room which is just a little bit smaller than yours(1300 sq ft), building is not insulated very well, with drafty wood floors and 20' tall ceilings. The shop stays around 80-83 during the hottest part of the day in the worst part of summer and i can usually keep it around 75-78 or so in the mornings and after the sun starts to go down at night.
there is a smaller 10,000 btu unit in the grinding room and 2 ton central for the office/living quarters.
the electric bills can be a bitch but it's better than the alternative=being miserable, unmotivated, sweaty and hot all day.
i do intend on supplementing the opposite end of the shop with a portable 12,000 btu unit this summer since our heat and humidity down here is pretty extreme.
search CL for window units, i bought mine in almost brand new condition for 300 bucks delivered.
it was a $750 unit, used only for a few months while the PO was finishing his house. He delivered it right to me, in the original box with the remote and all.

We had a insulated just under 1400 shop at first and used a 21k btu air, but I live where 90% plus of the time it cools down after the sun sets enough to open everything up. So, I've found that a big exhaust fan is a great addition to keep things cooled after turning the air off for the day. There is a lot of stored heat in a building that the air unit has been cooling also. In the morning having that exhaust fan on a timer and turning it on in the cool of the early morning, long before sunrise, goes a long way toward reducing your cooling cost during the day.

Another big heat source for us in the summer was the roll up door. Mid and late afternoon sun would hit it and it was like turning on a heater. We had a couple of roll up door companies look at it and they all said what we had already knew. This roll up was of the type you cannot put insulation on.

We came up with a solution, but my point here is to look at the inside and outside of your building. What simple things can you do to improve it's reflectively and along with the insulative (is that a word?) properties?


One of our past commercial neighbors painted his metal auto shop a dark brown, black, also dark green to match his logo and trucks... I have not been over there since he did it... now that its warming up (90 today). I think I would have gone with maybe a off white and kept the logo small.

Steve

Have used a 24kbtu window unit in 3 shops, 900 to 2700 sq feet. Keeps it sane but it is never really turned off. Hit the energy saver switch at night Usually keeps it dry and below 82 or so. Better than nothing

Look at minisplits

Mini-splits are preferrable over window units as long as they're not used in a space where the evaporator coil is subject to airborne contamination. In a machine shop that's generating any significant amount of coolant mist, I'd stay away from the mini-splits.

Condensing moisture out of the air will result in coil contamination by coolant goo and dirt over time. Its relatively simple to pull a window unit out, take out half a dozen screws to remove the sheetmetal housing, and wash the unit out with a water hose. This isn't an option with a mini since you'd have to start by disconnecting the refrigerant lines to remove the indoor section for cleaning.

Minis are 30-40 percent more efficient than window units if you look at products that have reliable EER numbers. But coil contamination can quickly overcome that efficiency advantage and leave you with a unit whose actual operating power consumption makes it less efficient than the window unit, assuming you give the window unit a yearly bath. IMO, this is a case where its not worthwhile to spend twice the money on a mini, as any actual savings over time would be dubious at best.

Anyone who's installing a central system in a machine shop should make provisions for future cleaning of the evaporator coil as well. The coil is going to get fouled over time, and its a lot simpler to remove an access door for cleaning than to take a pair of snips to the ductwork down the road when the thing is plugged up to the point where it will barely pass any air.

I you go with window units be sure you understand that they will cool the air below and not above the points of intake. Just as with heating, fans and circulation will be helpful to keep temps even throughout the shop, but ceiling fans will de-stratify the air but you end up cooling to full room height. An exhaust fan placed high up is a big help for whenever it's hotter inside than out and the AC unit(s) have trouble keeping up. (IIRC you can go to 16k BTU with a 110v 'window-shaker', if that matters.)

In our assembly plants (GM) fans were provided for each workstation by local agreement. It was specified by plant policy that all must direct flow in a particular direction thru each building vs swirling hot air back & forth. Plan for some flexibility if you might have to rearrange fans/ACs later to cool the shop evenly, and for cleaning coils if you use coolants often. Having AC doesn't mean your 'iron' wouldn't benefit from a dehumidifier as well. YMMV, but all units/devices become part of a system and have to work together.

I had small 20x35 block shop in Maryland for 20 years
Mounted the window unit almost at the (10 foot) ceiling height thru the block wall.
Put a circulating fan on the opposite wall at the far end of the shop pointing back for a circular air flow.
Installed clear Sq. glass block for the window for natural light and kept the thiefs out.
Humidly was almost none existent.
Something to think about..
Robbie

On our old shop we had very good insulation and 1600 Sq feet with 9 foot ceiling. We used a central system with all the ducts attached to the ceiling to keep them away from the attic heat. A 2 speed, 3 ton unit was sufficient. As far as I know it always ran on the low speed. This was in south Texas were the summer heat is extreme, but I think you will need some duct work to spead your cool air otherwise you are going to have some hot spots. I think a central unit would save you a lot on your electric bills as it would have higher effeciency. Two or more split units would be a second choice on efficiency. With either a central or split units your building will be more secure.

24x32 with 10 foot walls, well insulated here. I have a 5000 BTU window unit and a ceiling fan. It won't keep up on temp, but it removes an unbelievable amount of humidity. When its 95 outside with 90% humidity, its 80 degrees with 25-30% humidity inside. I love it, its feels like 65 degrees. My wife comes out in the shop and thinks it is more comfortable than in the house at 70. Keep in mind that if the unit runs more it pulls out more humidity.
Tony