Another Mini Split Question - SoCal

[fastsvo]

I have a partially insulated attached three car garage @ 660sqft.

I say partially insulated, because the room above it and the walls facing the interior of the home are insulated, but not the sides and it has a wooden garage door with windows. I am finding decent deals on 18k MiniSplits, but have been told in the past that a 24k is the right way to go. Given the hot climate in the summer, how bad will this be with an 18k unit? Will it just take longer to cool or perhaps not be able to cool down to a certain comfortable temperature?

 

[Jackfre]

I’d go with the 18 and let it work. Then I would insulate the areas where the building is deficient. Rockwool is pretty easy to handle. Point is bring the load back to the equipment rather than buying bigger.

 

[fastsvo]

I’d go with the 18 and let it work. Then I would insulate the areas where the building is deficient. Rockwool is pretty easy to handle. Point is bring the load back to the equipment rather than buying bigger.

I do see the point of letting the unit run longer rather than short cycling it. My other thought was it might be cheaper to buy a 24k and let that run without spending additional $$ of insulation (I would have to cut holes in the drywall and blow it in). Not sure, which is the smarter path here?

 

[txvwnut]

18k and insulation is the smarter way to go. My building is two levels and roughly the same square foot as the OP's on each floor. I have a dual zone mini split with 18k heads. The upstairs is insulated but really needs more or better insulation to be correctly effective, the lower floor is not insulated at the moment. I keep both stats on 80 in the summer and 62 in the winter and use fans to circulate the air when I'm in the shop and keeps it comfortable for Texas weather.

 

[ericm]

The insulation will cost less over time than the bigger mini split and the power to run it. Power's not cheap in California. It also will make the space more comfortable.

You can run a load calc and have some actual numbers instead of picking a number out of the air. I used loadcalc.net. With some practice I got to within 10% of the load calc the HVAC company did for my house, and that was with slightly simplifying a complex house shape. I sized the mini splits for my shop based off my load calc and they have handled the cold just fine. We need more heat than cooling here so if I undersized them heating is where it would show.

If you use loadcalc.net make sure to look at every field and put a value in it if appropriate. Otherwise you get a number that is low.

You can also use this to figure out how much less of a mini split you need when insulated.

 

[WildBill]

I do see the point of letting the unit run longer rather than short cycling it. My other thought was it might be cheaper to buy a 24k and let that run without spending additional $$ of insulation (I would have to cut holes in the drywall and blow it in). Not sure, which is the smarter path here?

Mini splits ramp up and down as needed, they don't cycle. Its really hard to oversize them like you can with a traditional unit. If the 24k is just a couple hundred more I would get it, and also think about insulation at some point. Blow in is pretty easy to do and you can rent the equipment for cheap. The 24k will recover better from the doors being open and hot cars coming in.

 

[PoorUB]

Insulate! I don't care which unit you buy, you need to insulate! On a hot California day a 24K might no keep up. If you insulate reasonable well a 12K might cool it. Three insulated overhead doors will be a killer too. I would plan on replacing them at some point.

Guys here on GJ have tried to do this (cool the garage with uninsulated walls and doors) in the past and most have failed!

What is you intended use of the garage? Have you considered closing off one section and insulating that well and putting in an insulated garage door?

 

[dscheidt]

Mini splits ramp up and down as needed, they don't cycle. Its really hard to oversize them like you can with a traditional unit.

You need to pay attention to the specs of the unit you install. There are splits with turndown ratios of 6:1, but most are around 4. There are some, usually larger ones, with a turndown of just 2:1 on cooling -- meaning the minimum output is half the rated output. If you installed a 24k unit with 2:1 turndown, where 18K is the correct size, ti will be oversized, and short cycle. There are also a lot of 18K units that are really 24K units, with the output limited by software, meaning the minimum output of both is the same.

 

[fastsvo]

You need to pay attention to the specs of the unit you install. There are splits with turndown ratios of 6:1, but most are around 4. There are some, usually larger ones, with a turndown of just 2:1 on cooling -- meaning the minimum output is half the rated output. If you installed a 24k unit with 2:1 turndown, where 18K is the correct size, ti will be oversized, and short cycle. There are also a lot of 18K units that are really 24K units, with the output limited by software, meaning the minimum output of both is the same.

I am looking at this unit, which I can get for around $700.

https://www.homedepot.com/p/Hessaire-DIY-22-5-SEER2-18-000-BTU-WiFi-1-5-Ton-Ductless-Mini-Split-Air-Conditioner-Heat-Pump-Variable-Speed-Inverter-208V-230V-H18FB2/333810451

 

[fastsvo]

Insulate! I don't care which unit you buy, you need to insulate! On a hot California day a 24K might no keep up. If you insulate reasonable well a 12K might cool it. Three insulated overhead doors will be a killer too. I would plan on replacing them at some point.

Guys here on GJ have tried to do this (cool the garage with uninsulated walls and doors) in the past and most have failed!

What is you intended use of the garage? Have you considered closing off one section and insulating that well and putting in an insulated garage door?

The garage will hold three cars and when lucky, I will sometimes work on them. The wooden garage doors at some point down the line will get replaced, but for now I can tack on bubble foil type radiant barrier against the doors if needed. Resealing them will also help with air leakage. In fact, closing off the foundation vents and gable vent inside is something I am considering as well. The gable vent can be converted to a forced air vent to exhaust car fumes when necessary.

 

[fastsvo]

The 24k will recover better from the doors being open and hot cars coming in.

This has me rethinking the 18k unit.

 

[Junkman]

A friend told me over 3 decades ago that energy would remain expensive and that its price would never go down. The only hedge that you have to save energy is to improve insulation. When he built his home in 1992, he insulated the attic with 12" of open-cell foam, built the walls with 2x8 on 24" centers, and also filled them with foam. At that time, foam was relatively new and expensive. He has saved year after year on his energy bills because of his foresight with insulation. Today, there are better forms of foam insulation, and many people shy away from its cost. Looking ahead, what will energy costs be in 5, 10, or even 20 years? I don't think I will see the costs in 20 years, but I could see them in 10, and I know that my investment in foam is already paying off in just the last 3 years since I had it done. If you can't afford foam today, do the next best thing and insulate as best you can. Your pocketbook will be fuller because of the insulation.