40x48x16 Shop - Help with mini split sizing.

[Cncman08]

Look for opinions on mini split sizing. I have had a couple hvac companies quote to install a mini split for cooling of a 40x48x16 shop in south central MN. Three of them quoted a 2 ton mini split and the forth is recommending a 3 ton central air type set up. The building has 3 inches of closed cell on the walls and 18" of fiberglass blown in the attic. There is 2 inches of xps foam under floor and 3.5 inches of xps perimeter foam buried 24 inches vertical from top of concrete down. It has one 20x14 overhead door that is R19 and 6 double pane LoE 4x3 slider windows and one 36 inch service door. Will 2 ton be able to maintain 70°? I understand that recovery from opening the over head door may take some time and would be ok with that. The door will not open that often. The building will be used for personal auto repairs and just generally hobby activities. Does any one have a comparable size that is using a 2 ton system?

Sorry I did not say this, it will be for cooling only I have in floor heat for all my heating. I am also planning to leave it on all the time, not only when I'm in there.

 

[PoorUB]

IMO, 2 ton is a bit small for that square feet and wall height.

I have 1-1/2 ton in a 24x38x9 and it keeps up fine, but if I wait to fire it up when the shop is warm it takes 2-3 hours to satisfy. You have twice the square feet and close to four times the cubic feet. I am not convinced a 3 ton will do it!

Another option to consider is put in the 2 ton and see with the understanding you might be installing a second 2 ton down the road.

 

[Cncman08]

IMO, 2 ton is a bit small for that square feet and wall height.

I have 1-1/2 ton in a 24x38x9 and it keeps up fine, but if I wait to fire it up when the shop is warm it takes 2-3 hours to satisfy. You have twice the square feet and close to four times the cubic feet. I am not convinced a 3 ton will do it!

Another option to consider is put in the 2 ton and see with the understanding you might be installing a second 2 ton down the road.

Installing a second 2 ton if one 2 ton doesn't keep has been one option that has crossed my mind. I do intend to basically keep it a constant temp. I will not be turning it on and off depending if I'm out there or not, I will set it and forget it.

 

[PoorUB]

Installing a second 2 ton if one 2 ton doesn't keep has been one option that has crossed my mind. I do intend to basically keep it a constant temp. I will not be turning it on and off depending if I'm out there or not, I will set it and forget it.

With two units you could set them one degree apart and let one do most of the work, and the second will come on as needed.

 

[Jetsurgeon]

IMO, 2 ton is a bit small for that square feet and wall height.

I have 1-1/2 ton in a 24x38x9 and it keeps up fine, but if I wait to fire it up when the shop is warm it takes 2-3 hours to satisfy. You have twice the square feet and close to four times the cubic feet. I am not convinced a 3 ton will do it!

Another option to consider is put in the 2 ton and see with the understanding you might be installing a second 2 ton down the road.

I am looking at a 36000 BTU (3 Ton) unit for my 24x50x10, but I am in Central FL...I will have 2" on the wall and 3" on the roof of closed cell foam...

 

[dcg9381]

Will 2 ton be able to maintain 70°? I understand that recovery from opening the over head door may take some time and would be ok with that. The door will not open that often. The building will be used for personal auto repairs and just generally hobby activities. Does any one have a comparable size that is using a 2 ton system?

I assume heating, not cooling?
I have a 40x60x14, but in TX, takes 4 tons (2 x 24BTU) to cool it - similar insulation.
Heating - I assume your guys are watching the "efficiency" of these units at low temps.

As "partial use" - I'd encourage you to "over HVAC" with mini(s). Residential calcs are for full time heat/cool. I'm assuming moisture isn't an issue (which it may be).

 

[Steve W.]

My shop area is 24 x 30 x 8. Subtracting the stairway to the upstairs and the bathroom, it's more like 24 x 25 x 8. R-13 insulation all around the walls. R-13 in the ceiling between the two levels and more R-13 at the roof, between the attic trusses. One 10 x 7 overhead door, one 36" entry door, four 24 x 40 awning windows (double pane). Not sure what' below the floor, but there is something there.

One 2 ton (24k BTU) mini hung from the ceiling. Over this past winter, I let the shop cool down overnight, it got down to about 50°. Turned the mini ON. About an hour later, it was 70°. That was with outside temps around 30°.

My 24 x 25 x 8 is 4,800 cubic feet. Your 40 x 48 x 16 is 30,720 cubic feet, which is 6.4 times as much. Not saying you will need 6.4 x 24k BTU, but I feel that 24k BTU will not be enough.

Not knowing your layout, would it be possible to put one unit in an offset location (near where you might do most of your work), leaving the option to put a second unit to cover the remainder of the shop? Not quite "zone heating", but might reduce the load a bit by only running one unit if that's all that's necessary, and also providing some redundancy in the event that one of them fails.

.

 

[giddygoat]

Using it just for cooling and leaving it on you likely would get by with a 2 ton. I am in southern Mn, shop is two areas 24 by 40 each, one is 14 ft high the other is 10, two overhead doors, no floor insulation walls are 6 inch fiberglass with 1.5 inch foam on lower cement walls. Ceilings are two ft plus fiberglass. 2 ton will drop it 25 degrees in 2 to 3 hours, has no problem keeping up, runs so cheap I just leave in on all summer. Nice that cool air stays low so no need to run ceiling fans unless you have an upstairs area. I use it for heat in the fall and spring but it is a 15 year old unit so it does not do well for heating. I would compare the 2 and 3 ton mini splits cost may not be that much higher for the 3 ton, but I think it would not make much difference in running costs due to the way these units ramp up and down as needed.

 

[DentalDart]

I have a heat pump in my 30x40 with 10.5ft tall ceilings. Batts on the walls, blown insulation ceiling. (Don’t know how much of either, probably not as much as you have). Inside walls are finished with metal panels.

I bought a used 2.5 ton heat pump on Facebook marketplace for 500 bucks 2 years ago. Keeps it 65-70 during the summer then can have it 70 degrees during the winter with ease. Takes about 30 minutes to heat or cool it. I leave it on all year long.

My big shop, 40x40 and is insulated like yours minus the foam under the concrete. I’ll probably do a 36k btu mini split because I believe these run on 30amp breakers instead of 60 like the heat pump.