Sizing a Minisplit

[ddickey]

I had a Daikin at my old place so I'm looking at those. They say 18kBTU for a 1000' area.
Mr. Cool's site says 24kBTU for a 1000' area. My shop is very spray foamed, 1280sqft. I'd rather undersize some than oversize. The ac or dehumid modes will be on all the time.
Anyone have experience with sizing? Is there something different about the Daikin?

EDIT: I checked Mitsubishi's site and they state 24K for 1000sqft also.

 

[tq60]

Depends on your local climate and build.

Here in central ca the "generic" formula is 1 ton (12000 BTU) per 500 square foot of normal space.

So call a local HVAC provider and ask for same or If You have hvac in your home then do some math, divide square foot of home by ton of unit.

Sent from my SAMSUNG-SM-G930A using Tapatalk

 

[rabler]

Climate and temp preferences are a big factor. Also, are you planning on 24x7 or just kicking it on when you need it? On demand needs quite a bit bigger. Online Sizing is usually based on house needs, not shop use. Are you counting on your unit for heating in winter too? In Mn that will be more problematic.

I have an 18k unit in a shop 800 sqft shop, minimal insulation, 12’ ceiling. Plenty of cooling and heating. But southern Indiana is a different climate.

If you’re leaving it on as you say, and not counting on heat, 18k is plenty.

 

[ddickey]

Yes, the ac will be left on during the summer. Heat will only be for cool fall days as I have infloor heat for the winter.
Also I will not have it 70 degrees either. more like ~ 75°F. I hardly ever ran the old unit in AC mode as the dehumidify mode kept the garage cool enough.

 

[rabler]

I guess you'll be fine then. And while it is a guess, my experience is that the manufacturers have little to loose by recommending an oversized unit. For example, based on 1000 sq ft workshop/garage, I purchased an 80,000BTU gas heater, the next size down, 50,000BTU was rated for up to 800 sq ft. I can walk in with the shop full of iron and air temp below freezing, and have it up to 60 degrees (my normal winter work temperature) in less than 10 minutes. No doubt in my mind I could have used the 50,000 BTU unit, or even the 30,000, but my shop is also well insulated.

How do you like the in-floor heat? Electric wire or water based? I'm planning out a new shop and thinking of putting in water lines in the floor to eventually heat the floor with water heated from a wood stove, as a supplement to a gas heater. I'll also be putting in a mini-split, dual system, tentatively 9000 + 18000 units on a 24K outdoor unit, to handle a 2000 sq ft shop.

 

[NC Rick]

I have a Mitsubishi in my 1000 sq/ft shop. Its bigger than my last unit which i undersized a little (i think it was a samsung or sanyo…) its gone with my memory. I like the extra power. These things are great amd do fantastic with humidity. My shop is not super well insulated but made of concrete and partly below grade. I like that when hot or cold out i can open the 8ft door for a time to grind or paint or move stuff and it catches back up quickly. Get the 24k and dont look back. Thats my recommendation. fwiw.

 

[ddickey]

@rabler I really like the infloor heat. Very glad I went ahead with it. I use a gas tankless water heater. I was really teetering on the idea of an electric boiler but when I realized it would need two dedicated 40 amp circuits I decided to go with the gas

 

[NC Rick]

Ummm, maybe mine is an 18000? I have another 1000 sq/ft unheated but insulated garage above the shop with steel and 4” of concrete above the shop. I think i had 16000 on the old unit. This thing rocks. The old one was good while it lasted. just not as good as this one. I like keeping humidity below 50%.

 

[rabler]

@rabler I really like the infloor heat. Very glad I went ahead with it. I use a gas tankless water heater. I was really teetering on the idea of an electric boiler but when I realized it would need two dedicated 40 amp circuits I decided to go with the gas

Yeah, we have NG on the street, so no reason not to use gas. Maybe I'll get creative and mix gas and wood to heat water for the floor.

 

[pdentrem]

Here we use 1 ton per 500 sq ft. Seems to be the convention.
Pierre