Mr. Slim sizing question

[Keith Avery]

I am just about finished insulating my pole barn. It is 30 by 48. I plan on walling off about half so that the back end of the barn will be my workshop with 30 by 26 dimensions. The ceiling is 12 ft at the bottom and slopes up to 15' in the center(trusses are about 11ft high). I have/am insulating with R-18 in the ceiling and the walls. The whole barn is also wrapped in a radiant barrier. The barrier supposedly adds a few in R-value. I have decided on a Mr. Slim ductless system but am not sure what size to get. I haven't been able to find a free manual J calculator online. I have read many of the AC posts but most don't mention tonnage of their unit and size of the shop just that it works well and most people seem to be in garages. I think I would prefer to undersize it a little. I don't need to get the shop to 70 degrees in the summer but 80 with low humidity would be nice. The 15k btu units seem to have the highest seer rating and it goes down considerably if I go up to 24k. I was also considering add a drop ceiling. I think I can put one of these in for less than 800 bucks and it would significantly reduce air volume, but it would be a lot of work and would limit ceiling height to around 10ft. The 15k unit is eligible for a small tax credit also but anything larger than that isn't efficient enough to get the credit. Also I am in middle Tennessee and it was humid and 96 today. Typical highs during the summer are high 90s and humid.
Anyone out there have one of these in a pole barn with relatively high ceiling? If so what is your insulation like? What size area are you heating/cooling? and whats the btu output of your unit? I greatly appreciate any input.

[Bob Cooper]

Keith...i cannot answer any of your questions but i'm curious how these compare, pricewise, to a standard hvac unit?

[Ray Knight]

I converted a 20x30 half of a frame/brick 40x30 garage to my workshop, 2x4 framed, insulated, live in southern Indiana, near Louisville, Kentucky, so size, insulation, climate similar to Tennessee. I have a 18,000 Ambience minisplit, keep it at 76 in summer, and 64 in winter, and works pretty well. runs most of the time when it is this hot. If you are going to run it part time, need more capacity to get cooled down, if you are going to use it full time, need less capacity to keep it there. Your other big decision will be do you do you get heat pump as well (Iwould recommend it), and if so do you get heating strips for the real cold days. I made the decision to give my budget and the economy a break, and did not get heat strips, when it get cold enough the heat pump doesn't work well (about <29F) I just shut it down and stay inside. That is just a few weeks a year up here, a bit less down there. Ray Knight

[Keith Avery]

Thanks for the replys. It looks like I am leaning toward the 1.5 ton unit. It is capable of a little over 2 tons(25.2k) of cooling output for up to 15 minutes and can heat at 100 percent of rated capacity at 5 degrees F. I have decided to go for the drop ceiling as I have come by some cheap troffer lights. This unit is 20 seer so it should be reasonable to run. Just the unit is going to be a little over 2k, but I think I can do most of the install myself and pay an HVAC guy 200 bucks to do the vacuum pump and final freon release to keep it under warranty. I can supplement the heat with a propane heater when its really cold if I need too. It also looks like the 18k btu unit is also eligible for the 10 percent tax credit but the 24k is not. The unit is am looking at is Mitsubishi MSZ-FE18(indoor) and MUZ-FE18(outdoor). Hopefully by middle of 2012 I will be getting somewhere, I make slow progress with 2 children under 4.

[Daniel Berlin]

Thanks for the replys. It looks like I am leaning toward the 1.5 ton unit. It is capable of a little over 2 tons(25.2k) of cooling output for up to 15 minutes and can heat at 100 percent of rated capacity at 5 degrees F. I have decided to go for the drop ceiling as I have come by some cheap troffer lights. This unit is 20 seer so it should be reasonable to run. Just the unit is going to be a little over 2k, but I think I can do most of the install myself and pay an HVAC guy 200 bucks to do the vacuum pump and final freon release to keep it under warranty. I can supplement the heat with a propane heater when its really cold if I need too. It also looks like the 18k btu unit is also eligible for the 10 percent tax credit but the 24k is not. The unit is am looking at is Mitsubishi MSZ-FE18(indoor) and MUZ-FE18(outdoor). Hopefully by middle of 2012 I will be getting somewhere, I make slow progress with 2 children under 4.


I have this unit in my smaller shop, and I love it.

You will be surprised how far it can push air

[Eduard Nemirovsky]

I got same units about 2 years ago for my 20 by 24 shed. Insulated with spray foam, climat practically same as in TN - humid and hot at summer and cold enough in winter. Unit work perfect, I am keeping 74 F summertime and 64F winter. I would strongly recommend Mr.Slim for anybody.
Ed.

[Tom Grant]

It sounds like you're on the right track Keith. In the HVAC world bigger is definitely not better.
Here is a great article on HVAC misconceptions: http://www.bestofbuildingscience.com/pdf/Smart%20and%20cool%20the%20art%20of%20air%20condit ioning%20HEM_SP05_p46-52.pdf