Mini Split Sizing 30 x 30' 14' ceilings, Check Manual J

[bmwpowere36m3]

I've ran a number of calcs using Slant-Fin for heating and sized the mod-con and panel radiators in the house very accurately.

So for the detached garage:

• Location, southern CT
• 30 x 30' 14' ceiling, gambrel roof (scissor type truss)
• Walls are 10', including 2' stem wall
• R20 in the walls, but accounting for the uninsulated stem wall ~R16 (wall assembly).
• R30 in the ceiling
• Slab in uninsulated
• (2x) 10' x 9' overhead doors, insulated R16 on west side of building
• Entry door on south side
• (3x) 2' x 4' windows on south side, high up under overhang (6.5' to window bottom)

Using loadcalc for the cooling of the barn, I get this:

Am I missing anything? Sounds right, 12k minisplit should do?

 

[ndfastang]

Sounds low to me but I'm no expert. Then again, I keep trying to consider keeping the shop low like the house and the same with the heat. Interested to hear what the pro's have to say. I'm 30x48 with 11ft walls so not TOO far off.

 

[ROBZ71LM7]

I'm no pro, but your outside temp is 84 and inside 75 degrees. Just ensure this is accurate for your area and that 75 is the temp you want inside. Also consider how much reserve if any do you need if you pull a hot car in on a 90 degree day. I used the same calculate for my 1000 sqft garage and I feel the numbers are low. I'm purchasing my mini-split next spring.

 

[Mesozoic]

That Manual J calculation must be making some assumptions about the insulation values since I don't see any fields for entering that data. Also, the window R-values are missing. Perhaps use a different Manual J calc? My contractor used WrightSoft Right-J software, if that helps.

 

[Jim greengo]

Fits right in with the 500 sq ft per ton of cooling rule.

 

[yeldogt]

I have a very well insulated building 1600+ SF in PA -- it can be heated and cooled with 15kBTU. Remember that is maintaining temp.

My property is currently under construction so the propane has been disconnected ... it was heated with electric last years so I known what it can be heated ... same with temp AC.

Your mini should go about 9' max .... don't stick it way up high.

Have you done the relative cost calculations for different fuels .... what do you have available

 

[tomfrazier]

Please, where did you find this load calculator? Thanks

 

[justinjoyal]

That Manual J calculation must be making some assumptions about the insulation values since I don't see any fields for entering that data. Also, the window R-values are missing. Perhaps use a different Manual J calc? My contractor used WrightSoft Right-J software, if that helps.

The R values are entered in the previous step.

www.loadcalc.net

 

[ericm]

It looks like you need ~38k btus for heating (unless you'll be heating with something else) and ~12k for cooling.

 

[Bigblockyeti]

Seems low to me too but CT isn't going to get as hot as where I'm at. If/when I power insulate and chill my shed, I'm not sure 12K BTU will cut it with temps in the 90's and humidity to match. It's 16' x 22' x 12' and I will be insulating between the ceiling joists w/R30 at minimum so I won't have direct roof exposure to the insulation which may or may not matter. If I've got to open the doors, it will allow a lot of heat and humidity in very quick in the middle of summer and I need it gone ASAP. The plus side of most of the newer mini splits is a dehumidification setting which in some cases will be better for what's in the shed than cooling.

 

[Jackfre]

Try to get to the load calculator on Fujitsu's site. It drops assumptions made in some programs on duct loss etc. Ct needs dehu mostly as I recall. You do have a lot of cubes there with the ceiling height. I'd shade a bit higher to a 15 and with the Fujitsu you still get 25.3 seer and 13.4 hspf.

 

[bmwpowere36m3]

I'm no pro, but your outside temp is 84 and inside 75 degrees. Just ensure this is accurate for your area and that 75 is the temp you want inside. Also consider how much reserve if any do you need if you pull a hot car in on a 90 degree day. I used the same calculate for my 1000 sqft garage and I feel the numbers are low. I'm purchasing my mini-split next spring.

That Manual J calculation must be making some assumptions about the insulation values since I don't see any fields for entering that data. Also, the window R-values are missing. Perhaps use a different Manual J calc? My contractor used WrightSoft Right-J software, if that helps.

Yes, the calculator makes certain assumptions based on inputs on prior screens. Temps are based on location and R values on selections. In case, closest to me Bridgeport, CT, siding R15 insulation, ceiling under roof joists R30, concrete slab no edge insulation, low-e windows and wood hollow core doors.

WrightSoft is $500, so not great ROI.

 

[bmwpowere36m3]

I have a very well insulated building 1600+ SF in PA -- it can be heated and cooled with 15kBTU. Remember that is maintaining temp.

My property is currently under construction so the propane has been disconnected ... it was heated with electric last years so I known what it can be heated ... same with temp AC.

Your mini should go about 9' max .... don't stick it way up high.

Have you done the relative cost calculations for different fuels .... what do you have available

The minisplit will be cooling primarily... plan is a unit heater as I have NG at the house. This first winter will likely only have the minisplit for heat.

 

[bmwpowere36m3]

Try to get to the load calculator on Fujitsu's site. It drops assumptions made in some programs on duct loss etc. Ct needs dehu mostly as I recall. You do have a lot of cubes there with the ceiling height. I'd shade a bit higher to a 15 and with the Fujitsu you still get 25.3 seer and 13.4 hspf.

Have link? I see a document that discusses it on the "Fujitsu Portal"

 

[polizei1]

I run a 24k Mr. Cool DIY in my 24x32x18, well insulated. It's amazing.

 

[Mesozoic]

Yes, the calculator makes certain assumptions based on inputs on prior screens. Temps are based on location and R values on selections. In case, closest to me Bridgeport, CT, siding R15 insulation, ceiling under roof joists R30, concrete slab no edge insulation, low-e windows and wood hollow core doors.

WrightSoft is $500, so not great ROI.

No, not good ROI for an individual designing their own garage!

I'm just curious, for residential construction (or if your garage was attached to your residence), would it be sufficient to have those R-values mentioned for the siding and ceiling in CT? Also, hollow core doors for the garage? I was under the impression that those type of doors were typically for interior use only. For comparison (keeping in mind that my garage is attached and I have attempted to match the existing construction as much as possible) and in southern AZ (hot summers), my vertical walls are R19 with R38 ceiling insulation. Exterior man door is steel with something dense stuffed into it, not hollow. Garage doors are only R9.

Either way, you're on the right track. Just get the calculations right to size the unit correctly and you essentially cannot go wrong with any of the typical ductless brands, including Mitsubishi, Daikin, Fujitsu, and I can't imagine that Toshiba/Carrier would be a bad option either.

 

[bmwpowere36m3]

No, not good ROI for an individual designing their own garage!

I'm just curious, for residential construction (or if your garage was attached to your residence), would it be sufficient to have those R-values mentioned for the siding and ceiling in CT? Also, hollow core doors for the garage? I was under the impression that those type of doors were typically for interior use only. For comparison (keeping in mind that my garage is attached and I have attempted to match the existing construction as much as possible) and in southern AZ (hot summers), my vertical walls are R19 with R38 ceiling insulation. Exterior man door is steel with something dense stuffed into it, not hollow. Garage doors are only R9.

Either way, you're on the right track. Just get the calculations right to size the unit correctly and you essentially cannot go wrong with any of the typical ductless brands, including Mitsubishi, Daikin, Fujitsu, and I can't imagine that Toshiba/Carrier would be a bad option either.

You have use the calculator to understand. Certain inputs, such as: windows, glass doors, doors and skylights... don't allow specific R value inputs. For example, there is no such input as insulated door, R value **. The choices for doors are: wood hollow core, wood hollow with storm, wood solid core, wood solid with storm, metal and metal with storm.

So go figure... You could, thru a variety of cases, determine what each selection is wrt to R value. Figuring the delta BTU and the associated SF of each component.

As far as sufficient or required insulation, nothing is required being a detached garage. If it were a home, typically 2x4 construction is R15 and 2x6 is R20. In the ceilings, I believe R49 is recommended. However with cathedral ceilings, all you'll get is R38.

The detached garage is 2x6 wall construction with R20 fiberglass insulation, however part of the wall is uninsulated concrete stem wall. Thus the overall wall R value is down to R16 (average).

For the ceilings, in my case there will be no attic access. Either it was batts or stapling up poly or partially sheetrocking and blowing insulation in. Using batts, R38 and R49 get real spendy quick... I compromised with R30, which seems to be the norm for detached garages around here.

 

[Cryptic1911]

I would definitely go bigger than a 12k. I have a mitsubishi 18k in an open 30x30 upstairs area above my garage. The walls are normal height, but vaulted ceilings and the 18k works good up there. I think it would be fine in a garage as long as you don't have the door open all day. I have a buddy who is supposed to hook me up with a free 18k for my garage, so I'll be in that exact scenario w/ 13ft ceilings.

 

[Evilcactuar]

No expert, but I would bump the cooling to a ton and a half for a little peace of mind, its a lot of cubic feet and the slab is a big, uninsulated thermal mass.