Shop electric heat & AC - seer rating considerations?

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Forum topic by WoodNSawdust posted 06-09-2015 12:51 AM 945 views 0 times favorited 4 replies Add to Favorites Watch
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1417 posts in 1682 days

06-09-2015 12:51 AM

Topic tags/keywords: workshop heating cooling ductless mitsubishi seer

Currently my shop is not air conditioned and I use a unvented propane heater for the winter. As I age I am getting more sensitive to heat & humidity which cuts back on time in the shop. With current temperatures it may be September before I can comfortable be back in the shop.

I talked with my Brian my HVAC person and he recommended that I purchase a Mitsubishi ductless system running on electricity. I suggested a SEER rating of 21. Internet research shows that I can purchase a SEER 19 unit sized for my shop for around $2000 and SEER 21 unit close to $4000. I used several Internet calculators that tell me how much different SEER values cost to run and one told me it would take 14 years to recover the difference in costs between the two units.

Several years ago I looked at the cost of running Natural Gas to the detached shop and bids were coming in for around $600 simply to run the gas line. I don’t have the room in the shop for a full size furnace & AC and would have to locate it in one of those plastic sheds (4’ wide x 2’ deep x 6’ high) outside and then run duct work into the shop.

If I go with the Mitsubishi ductless system I would have to locate at one end of the shop (16’ x 36’) and expect the unit to blow air all the way down the 36’ length of the shop.

Before committing to spend this amount of money I wanted to query the collective wisdom of this forum.

Has anyone used one of these ductless systems? If so what are your experiences?

Would you trust the values that the Internet calculators for SEER costs?

I am leaning towards the lower SEER (19) unit figuring that I can use the money I save to do other things and who knows what I will be doing in 14 years. Your view?

Thanks in Advance,

P.S. When the shop was smaller (16’ x 20’) I tried a 120V window ac unit and it could not keep up. I think that it was a 5000 BTU unit.

P.S.S. I looked into a 18000 BTU window unit with heater but it is too wide to fit into a window requiring that I change the structure and install a larger window.

-- "I love it when a plan comes together" John "Hannibal" Smith

4 replies so far

View alittleoff's profile


541 posts in 1782 days

#1 posted 06-09-2015 03:30 AM

I have a shop that’s 24×24 with a 2 ton system that works fine. I closed in a porch on the shop and instead of running more duct I decided to buy a ductless system for the room only. I’ve had it for three years now and it does not do the job. It blows air maybe 10 ft and that’s it. I have a small 110 volt window unit that I put in a window that cools the whole room fine by its self. The 1 ton ductless unit I bought is a Daikin. It’s turned off right now and won’t be turned back on till winter get here. It’s funny that it will heat the room but won’t come close to cooling it. I’ve had it checked 2 or 3 times and no one has yet to come up with what’s wrong with it. The window unit works fine and is not even in a good location. I’m thinking about just going back and add ducts to my existing unit and be done with it. If you get one i hope it works better for you than mine does.

View crank49's profile


4032 posts in 3477 days

#2 posted 06-09-2015 04:36 AM

My shop is 16 ft by 24 ft, so about 2/3 of yours? My ceilings are 9 ft and I have a storage attic and upstairs office also, but just don’t try to cool the upstairs.
I bought a new Frigidair 11,000 BTU window unit last year and cut and framed up a hole in the wall to mount it.
It does a good job here in southern Tennessee, and only cost $300. Two units like mine would probably do a great job in your shop.

BUT, cheap window air conditioners are typically 10.3 SEER, so it won’t compete with a mini split system for economy of operating cost. It does have an Econ setting that I really like. It starts the fan and runs it for about 15 seconds every 15 minutes or so. If the temperature is not above the thermostat setting it then shuts the fan off and waits another 15 minutes before checking again.

As far as paying double to get from 19 SEER to 21 SEER, NO WAY.
I’d add solar panels and an inverter with that extra $2000 and have free air conditioning for most of the hottest part of the day.

But, then that’s how I make my living so I could be a little biased.

View soob's profile


271 posts in 1714 days

#3 posted 06-09-2015 01:43 PM

Internet calculators for SEER vs cost are based on HOUSES that are cooled all the time. Your shop is 500 square feet and it sounds like you don’t use it very much. You also didn’t mention insulation; if your shop is not insulated you’ll be throwing money away cooling it all day when it’s not in use regardless of how efficient the air conditioner is.

My recommendation would be, instead of getting an expensive, high efficiency unit that’s sized to cool the space continuously like a house—buy several small ones that can bring the temperature in that large space down quickly. 12k BTU window units are available in compact sizes that should fit in a smaller window that can house a 5k BTU (which is undersized, I agree).

View KCtennessee's profile


1 post in 1641 days

#4 posted 06-09-2015 01:48 PM

I agree with Crank. No way is going from 19 to 21 SEER worth double. Stick with the 19 SEER.

I have a friend that has ductless systems in his shop and the only complaint is the dust that always clogs up the filter. They need to be washed once a week if you’re using the shop even sporadically, and yes he has a very good dust management system.

-- It's not how many notes you play, it's how you play the notes you play.

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