Detached Garage - Ductless MiniSplit

[Pettrix]

For my insulated detached garage (1,200 sqft). I was thinking of getting a 1 ton ductless minisplit unit to help cool it in the summer and provide a little heat in the winter, if needed. Would the 1 ton be undersized for an insulated garage? (R-30 walls/R-40 roof/R-8 car entry doors) I'm in Zone 4B (High Desert)

Which option should I go with:

A – 1-Ton - SEER2=24.00, HSPF2=9.00, Able to heat down to -22F = $1,200 for the unit

B – 2-Ton - SEER2=17.00, HSPF2 = 6.7, Able to heat down to 5F = $1,200 for the unit

The 2-ton unit is not as efficient as the 1-ton unit, hence the pricing difference. Which would be the best unit for the garage?

 

[Code54]

Look up load calculations for HVAC and run the Calc. You need a lot more info, like number of windows, directions of the windows, and most importantly the height of the garage as the volume of air matters. You need a large unit for a 16’ high 1200sq ft garage than an 8’ high garage.

 

[Code54]

HVAC Load Calculator - Manual J Calculation | ServiceTitan

Our free, easy-to-use HVAC load calculator will help you determine the necessary thermal output capacity (in BTUs) of any residential building.

www.servicetitan.com

Here is an example

 

[WM75Guy]

I don't think you will have enough capacity if 12,000 BTU = 1 ton, as I have been told. We have a 30'X40' insulated metal shop with a 14'X20' wood framed insulated room inside for stained glass work. The HVAC company put in a 12,000 BTU Daikin mini split for that room. Added on to the west side is our our 12'X20' shop office. It is insulated with metal walls outside and inside. The HVAC company used an 18,000 BTU Daikin mini-split because of the higher heat load. The main shop has a 50,000 BTU electric heater just to keep the plumbing from freezing in the winter.

 

[Pettrix]

Appreciate the info.

Last winter the garage never got below 58F.

There are NO windows and the height of the garage peak is 16' as a gable so it starts at 10' and peaks at 16'. There are TWO insulated (R-8) car entry doors (18x8) and an insulated side entry door (R-7).

The garage walls are high-mass (concrete) so the R-Value is R-30 but studies show the Effective R-Value can be as high as R-50.

I think I will go with the 2-Ton unit...

 

[mrmikey]

Nice garage. Looks like a long span for those beams, what size are they?

 

[FPGT72]

I think the real question is how bad is it in the summer. Mine hit -20 last winter, and the heat just could not keep up. I drained everything when I learned that cold snap was coming.

Mine has a loft now, and I store as well as work up there, I have a "large" 240 "window unit" in the shop and that keeps the down stairs nice enough to not sweat like a pig, my area is really getting the humidity out. But up stairs it is a different picture. You can have 75 down stairs, and well over 100 up. I am thinking of a small minisplit to help out when I am working up there.

 

[2manyrocks]

Maybe worth mentioning that some mini splits are rated to provide heat in temperatures as low as -13F where some others won't do that. If heating in very low temps is a concern, you'll want to check the specs before buying. There may also be a loss of efficiency in providing heat in very low temps. Last issue is the BTU capacity for heating is usually higher than the BTUs required for cooling. The BTU required to heat 0 degrees up to 72 is more than the cooling BTU required to bring 100F down to 72.

For a loft, heat rises upward so adding cooling at loft level should make it more comfortable.

 

[bdhsfz6]

I installed a 12,000 BTU Daikin mini split in my 900 sq ft insulated garage / shop with 10' ceiling and two insulated 8' x 9' overhead doors. It works fine here in the northeast US with temps from -10 to 95F.

I chose a WiFi model that I can control from the house. I turn it on a few minutes before I go out and it's at the perfect working temp.

If you plan to leave the unit on 24/7, a 12,000 BTU (1 ton) unit would work to maintain a constant temp. If you plan to use it intermittently, you might consider an 18,000 BTU model, or even the 24,000 BTU (2 ton) unit which will bring the building up (or down) to temp much quicker.

I'm no expert though, so this is just my 2 cents.

 

[3Ts]

You really need to do the load calculations. I have an 864 sqft cabin every well insulated that my wife does her crafts in and it is heated and cooled year round. The HVAC guys said a 2 ton unit would be required based solely on the sqft. The load calculations said about 13,000 btu so just over 1 ton. I ended up putting in a 1-1/2 ton unit and it is more than is needed.

Also, the air sealing of your doors is going to be very important. I found the air infiltration factor to be a major factor in the load calculations.

 

[Pettrix]

Nice garage. Looks like a long span for those beams, what size are they?

Span is 48 feet.

Beam is 21" tall x 6.50" wide with a thickness of 0.45 at the top and bottom plates and a web thickness of 0.35. Yield strength of 36,000 psi. The beams weighed 2,110 pounds per beam. Price was about the same at $2,200 per beam.

Steel plates were embedded into the wet concrete during the wall pour. The beams rest on these steel plates and were welded down to the steel plates.

 

[mrmikey]

Thanks for the reply Pettrix. The original pics didn't do their size justice, they're definitely big enough LOL.

 

[Pettrix]

Thanks for the reply Pettrix. The original pics didn't do their size justice, they're definitely big enough LOL.

No problem. I didn't want any mid-span supports as that would get in the way of having an open space and require footings inside the garage. So the engineer called out for these beams to span that distance without mid-span supports. These style of beams are used in NYC skyscrapers.

I can't get a 53' semi truck onto my rural lot so I had to unload the beams at the street and then use a telehandler to drive each beam, one at a time, over 1 mile to get to my site. It was a little unnerving having that beam in the air while going down the road.

 

[ponytug]

@Pettrix Wow. I'm sorry that you didn't shoot video of moving the beams! That is a lot of mass and inertia, and the photos make it clear that it has to be up in the air some of the time to clear the shrubs and trees.

It is a gorgeous garage, and some thing to be proud of.

All the best,

Peter

 

[Pettrix]

@Pettrix Wow. I'm sorry that you didn't shoot video of moving the beams! That is a lot of mass and inertia, and the photos make it clear that it has to be up in the air some of the time to clear the shrubs and trees.

It is a gorgeous garage, and some thing to be proud of.

All the best,

Peter

Thanks! The garage has taken a lot of work and money to get to this point. I work full time and then work on the garage after work and on weekends. So it has taken a while to get to this point.

The beam had to be lifted up over 20' at times to clear the juniper trees. That got scary as being so high up in the air, the wind gets it and it starts to move around. I was fearful the beam would fall. We had it strapped but it got sketchy at times. The telehandler has a wide base so it's pretty stable but everything has it's limits.

I also used polyurethane SIPS for the roof. We had the garage beams and roof installed in just 1 day. Once the beams are in place, the SIPS panels are labeled and go on pretty quickly with a crew of around 8 people. They get screwed down into the wall top plates (4x6 wood) and the steel beams had wood top plates installed on them for an anchoring point. The SIP screws are 9" in length.

Just to punish myself even more. I am also building a house now

 

[mrmikey]

Now that's what I call a balancing act .
I was watching a series where a couple built a house using those SIPS, I think their roof was 12" thick if I'm not mistaken. Their roof turned out fairly good but there were voids in between some of the panels where the foam was supposed to be sprayed in the joints. I wasn't visible until the winter and it showed up by the snow melting where there were voids. It's the way to go especially for speed.

Just to punish myself even more. I am also building a house now

Does the expression, "sucker for punishment' mean anything LOL

 

[Pettrix]

Now that's what I call a balancing act .
I was watching a series where a couple built a house using those SIPS, I think their roof was 12" thick if I'm not mistaken. Their roof turned out fairly good but there were voids in between some of the panels where the foam was supposed to be sprayed in the joints. I wasn't visible until the winter and it showed up by the snow melting where there were voids. It's the way to go especially for speed.

Does the expression, "sucker for punishment' mean anything LOL

I did an ICF (6" concrete core with 5.50" of EPS) wall and polyurethane roof SIPS. There are basically 2 types of SIPS (polyurethane core vs polystyrene core). The polyurethane is stronger, has a Class A fire rating, and has higher R-Values but it does cost more. I used SIPS of America out of Missouri. Panels are 6.50" thick and get a R-40 value.

All panel connections are T&G, double gaskets, foam/taped and sealed on both sides with SIGA tape. It makes them air tight at the connections.

Another nice thing about the SIPS is that they give you an overhang without having to frame out and build out soffits & fascia. Once the panel is installed you have a 24" roof overhang that is ready to go. I then had it covered with metal fascia and soffit pieces. There is also no need to run soffit vents, which is important in wildfire areas like mine. Embers are enemy #1 and any soffit/gable/ridge vents are an access for embers.

Building design should be specific to geographic locations. Concrete and steel are your friend in wildfire areas. Overhangs work great in desert climates to keep the sun off the walls but work against you in high wind/tornado areas as overhangs become a lift point to peel off roofs. Hip roofs work best in tornado areas. Gable roofs do not. There is no one size fits all when it comes to building. There are pros/cons to each type of material and design.

 

[2manyrocks]

Great pictures and a great story, too.

 

[ponytug]

Thanks! The garage has taken a lot of work and money to get to this point. I work full time and then work on the garage after work and on weekends. So it has taken a while to get to this point.

The beam had to be lifted up over 20' at times to clear the juniper trees. That got scary as being so high up in the air, the wind gets it and it starts to move around. I was fearful the beam would fall. We had it strapped but it got sketchy at times. The telehandler has a wide base so it's pretty stable but everything has it's limits.

I also used polyurethane SIPS for the roof. We had the garage beams and roof installed in just 1 day. Once the beams are in place, the SIPS panels are labeled and go on pretty quickly with a crew of around 8 people. They get screwed down into the wall top plates (4x6 wood) and the steel beams had wood top plates installed on them for an anchoring point. The SIP screws are 9" in length.

Just to punish myself even more. I am also building a house now

View attachment 873977View attachment 873978View attachment 873979

Oh, I get it, the garage was just a warm up run. You've set the bar (or should I say beam?) pretty high.

I look forward to a thread on the house build!

All the best,

Peter

 

[LDR812]

Really good thread! I’m planning to build a home soon and am going to investigate SIP - I had been planning on spray foam for cathedral sealings but like this much more