Help Sizing Mini Split

[Crowley]

Hello everyone,

Hoping to get help with a few general HVAC questions.

Background:
I'm building a 36x64 garage/shop. There will be a division wall that separates the garage and shop area which will create a 1300sq ft shop which is what I am heating and cooling. I'll be doing mostly woodworking in the shop. The walls will be R19, ceiling R38, and 2" rigid under slab. I used CoolCalc to do a ManualJ calc and came up with 14k cooling BTUs and 30k Heating BTUs. I'm in central Indiana. I've been reading up and understand that I don't want to over or undersize the system. That is making it a bit hard to land on a proper size. Its pretty humid here in the summers, so I'm wanting the AC to run for dehumidification.

Questions:

• I think I want to go the mini split route, but would not rule out ducted if it made better sense. Any reason I should consider ducted instead?
• There is a pretty big difference between my heating and cooling requirements. Do I use the bigger BTU requirement (heating) to size the system? Afraid that a 36k system would be too much cooling based on my calcs and I wouldn't get dehumidification or the system would short cycle.
• Should I go with two 18k units instead of 1 36k unit? That way only one would cover my needs for cooling, but both for heating

Sorry if these are basic questions, I just couldn't find what I was looking for.

Thanks!

 

[Jackfre]

A multi or two singles will allow you to do as you suggest. Have heat capacity and flexibility in cooling and dehumidifier. Check the power requirements for a 36 multi. I believe it will be 30 amps. A 15 could work on a 15 amp circuit. 18’s take, I think a 20, but possibly a 15. Push those numbers around a bit compared to the Seer/hspf ratings. I think you will be better off with the mini than central, but I am biased.

 

[Crowley]

Thanks, Jackfre. Appreciate the insights. I was looking at some DIY kits from Mr Cool, Senville, and others. I'll do as you suggest and look at multi or multiple single units.

 

[mike93lx]

Will this be your only heat source as well? What do you have available for fuel? Just electric?

If so, I would probably get a 24k btu (they can throttle down and will also usually have a dehumidification mode) and then add an additional electric resistive heater to supplement.

 

[Crowley]

Thanks, Mike! Yes, electric is my only option. I had not considered the 24k option with supplemental resistive heat. That makes a lot of sense. I'll have to look into that some more.

 

[mike93lx]

Thanks, Mike! Yes, electric is my only option. I had not considered the 24k option with supplemental resistive heat. That makes a lot of sense. I'll have to look into that some more.

Baseboard heaters are pretty cheap to buy and install. Especially compared to upsizing a mini split

 

[Jackfre]

Baseboard heaters are pretty cheap to buy and install. Especially compared to upsizing a mini split

True, but this puts you in the cheap heat or cheap heater bind. Also, our op says he will look into a unit with back-up heat. You will not find a mini-split with elec heat back up. You cannot put elec Ht in a plastic cabinet.

 

[fwillison]

I'm in Tulsa OK and my LG Minisplit has been very impressive in terms of its heat output in the winter. I have a ventless gas fireplace that I inteded to use to supplement but have never really needed it. The minisplit's heat pump works great. So does the ac, but Ive had problems with extreme mold growning in the evaporator/wall unit such that I had to install a dehumidifier during the summer to prevent it. I also installed a UV light system on the wall unit, but I believe the dehumidifier is what has been most effective for the mold growth during summer ac use.

 

[Crowley]

Thanks for the additional info. I've not heard of mold issues in mini splits before, but something I will look into.

Thinking more about things, I'd rather take the hit up front on the equipment than pay for the additional electricity use that resistive heat would require.

Thanks, all.

 

[mike93lx]

Thanks for the additional info. I've not heard of mold issues in mini splits before, but something I will look into.

Thinking more about things, I'd rather take the hit up front on the equipment than pay for the additional electricity use that resistive heat would require.

Thanks, all.

Upsizing the mini won't necessarily solve that. Heat pumps are only effective down to certain exterior Temps. That level varies between brands

I also had some mold in my mini, but it never came back after I cleaned it up once.