Help me select right btu mini split

[Jay Brain]

I’m here in NJ and looking to heat and my garage with a mini split set up

Here’s the specs

24 x 20 x 9 - 2x4 walls, I’m Going to fully insulate , drywall , has 4 windows , one big garage door

 

[LS6 Tommy]

I know it's not a critical space, but a Manual J load calculation is the most accurate way to figure it. The details listed are kind of vague.

Tommy

 

[OldSkool]

Manual J for sure otherwise you would just be guessing. Size your ductless for heat load as opposed to cooling load. It's a heat pump with no supplemental to back it up in heating mode. Look for a system that will give full heating capacity at 0 to 5 degrees. Mitsubishi has a "Hyperheat" line that is capable of doing just that. There are other brands that have similar capabilities. I'm partial to Mitsubishi. Been using them for 25ish years now and couldn't be happier. Nary a problem. There are a lot of other brands that are "disposable". I have replaced them with the Mistsu. Yes they are not the lowest cost. Tech support is outstanding. Phone is always answered. Never really needed them myself though. A good clean install will lend itself well to a "long hiccup free life". Good clean flare connections. Make your flares and if you don't like the way they look, do it again. Don't trust factory flares on premanufactuered line sets. Give them a good visual first. If they're clean keep'em. Electrical connections should be snug to tight at all connections especially the ground connections. A good long deep vacuum and you should be good to go.
I would suggest if you can carpet padding and carpet. Your floor is going to be a giant heat sink. Probably the highest part of your heatload next to your garage door. I would do everything I could to seal up your door tighter than a whale's **** at 40 fathoms. Watch the seams where the panels meet. DRAFTS will kill you. And a good insulated door at that.
Hope that helps.

 

[Jackfre]

I would go with a 12 or 15k unit. No larger.