Mini split sizing help.

[6togo]

I'm looking to size the mini split system for my garage which is 35x50' with 13' ceilings. It is 2x6 walls with R21 and R30+on the ceilings. It has 4 3x5' windows and two 10x10' roll up's. It also has a attic storage which will get it's own mini head not worried about that one it's easier more the lower level. I live In Delaware near the water so I'm more concerned about heating. I'm just looking to make it comfortable not living space hot/cold anyone have something similar? I have one Hvac guy that says he did a 24K unit in a 30x40x16' and said it works perfect and recommended it for mine but I'm thinking it might not be enough.

 

[pcmeiners]

I have (2) 12000 hi efficiency, (29 seer, hspf 13.8) , extra low temp Fujitsu units in my (35 x30, 10 ft ceiling r13 wall, r19 ceiling, 2 large garage roll ups, 2 windows,1 door) garage, only 1 turned on at this time. Was quite adequate when it was 7 ° F , was not even running at full at that temperature, ran intermittently . At 7° it was pushing out hot air.
Try not to over size, you are super insulated , 24k should be adequate if you get a decent unit. I installed 2 units as smaller units are more efficient and if one should fail, I have spare to keep my tools warm and cosy, as I hate tools rusting from condensation.

 

[jack stand]

No matter the heat/cooling source it's all based on your load or to put it simply, the building size-volume and the insulation & window/door performance specs.
(Called manual J)

 

[Patrick Eubanks]

Mitsubishi recommends 400 sf / ton if heating is important. 12,000 BTU/To

 

[6togo]

I forgot to add it will be drywalled as well. I'm doing a 12K unit in the attic space which is 600sqft with 7' ceilings. If You go by Mitsubishi's guidelines I need 4.25 tons on the lower level and 1.5 upstairs. 6 tons seems like a whole lot!

 

[6togo]

I had a 18K head in my last garage which was 25x30' with a flat 9' ceiling on one side and a 12' valued on the other side. That unit did amazing in there you could raise the temp 30 degrees in 30 min. That was a Daikin unit like 20 seer and 12 on the heat side.

 

[pcmeiners]

Mitsubishi seems way over the top, best to use a calculator.

 

[Patrick Eubanks]

It’s always good to run a load on the space but Mitsubishi sizes it capacity based on its inverter technology it now uses. It’s sized off 400 per ton because the unit only provides proportional heating when it gets really cold outside. In cooling the system is able to operate at optimal speed by staging itself. It’s best to listen to the manufacturer’s recommendation.

 

[Notgrownup]

You can use the calculator on Alpine home air. This is where I bought my Blueridge 18000btu unit for my shop.

 

[PoorUB]

I'm looking to size the mini split system for my garage which is 35x50' with 13' ceilings. It is 2x6 walls with R21 and R30+on the ceilings. It has 4 3x5' windows and two 10x10' roll up's. It also has a attic storage which will get it's own mini head not worried about that one it's easier more the lower level. I live In Delaware near the water so I'm more concerned about heating. I'm just looking to make it comfortable not living space hot/cold anyone have something similar? I have one Hvac guy that says he did a 24K unit in a 30x40x16' and said it works perfect and recommended it for mine but I'm thinking it might not be enough.

Personally, I feel 24,000 is a bit small. It might work 3/4ths the time, but in extreme cold you will need more. I might be tempted to go with two 18,000. One unit might keep up half the time and the other to pick up the slack.

Make sure you buy units that will heat in extreme cold so you get decent output in colder temps.

 

[6togo]

So I think I'm going to run 2-18k heads off one 3 ton unit and get a second single zone unit to run the 12K upstairs. It's cheaper that way instead of getting a 4 ton unit and run them all. Also it doesn't get real cold down the shore area maybe once a year might see single digits but mostly in the 30-40's in the winter. So if I mount the heads on the back wall blowing forward you think the heads will blow 50' forward?

 

[PoorUB]

You might want to add a ceiling fan to help move air.

It would be better to have the heads at the opposite ends of the building, but I don't think it is a deal breaker. Pus I understand the hassle of having one head at the other end. You might notice a bit of temperature difference from one end of the space to the other.

 

[Jackfre]

I would suggest that you go with single units rather than the 3 ton multi. I just looked at Fujitsugeneral’s on-line catalog and you are looking at a substantial reduction in efficiency with the multi vs singles. Also, the multi’s usually do not operate down to the temp you may require. Singles do. The redundancy factor should a single unit go down still gives you some coverage. Be very careful in analyzing the catalog specs. Fujitsu gives enough information that your eyes will be rolling in different directions when you are done, but it is all there if you take the time.