Ductless Mini-split AC/heat pump, determining size

[Arky217]

I'm considering putting one of these mini-split ductless heat pump/ac units in the house I'm building.
I need to know about what size I should be looking into.

The location is western, central Arkansas.
It can get above 100 for several weeks in the summer
and down near 0 for several weeks in the winter.

The house is 24' x48' (just under 1200sq.ft.).
It will have R28 in the floor, R23 in the walls and R40+ in the ceiling. It has 11 double pane, lo E windows.

The layout is basically an open LR,Kit,DR, 1 bath, 2 bedrooms, utility room and pantry.

I'm thinking of just a 1 zone unit installed in the LR or DR.

What would be the approximate size in BTU's that I would need for cooling and also for heating ?
And should I consider a model that has an auxiliary built in resistance heating strip ?

I've heard that the Mitsubishi Mr. Slim units are very good.
Anyone have any experience with them ?
Best place to buy, etc. ?

Thanks,
Arky

[Rob_O]

A 2 ton unit should be about right. You will have enough cooling on the hottest days and the mini-split can scale back its capacity on the cooler days. You will need some auxiliary electric heat, baseboard heaters are cheap enough

If your place has interior walls, your big problem will be getting the hot/cool air where you need it.

[n74tg]

Arky,
I will be using 4 ductless mini splits in my 1700 sf house.  I used the HVAC Calc program to size the loads and
discussed the results with our local mini split hvac guy (who also uses HVAC Calc for his load calculations).

For my house total need was two ton cooling, slightly less heating.  HVAC guy suggested I bump it up
1/2 ton for a total of 2.5 tons. 

If memory serves a one month license for software usage was $25; probably the best bucks I've spent on
the whole project; consider it.  Google it if you're interested.

Good luck

[Dave Sparks]

I use one Sanyo 3/4 ton for a 1800 sq ft home on solar. We have been running it from dawn to dusk for 3 years when there is sun. Our climate is different but I would think 4 units is a little crazy. They are easy to install so why not plan for more but install just one or two and add later if you need them. The Mitsibishy is good but also look at the Panasonic.

[CjAl]

Bigger is not always better with ac. If the system is too big it wont run long enough to remove the humidity. Learned this the hard way wyen i lived in ga and got a "deal" on a 4 ton commercial unit from a buddy.

[Rob_O]

Bigger is not always better with ac. If the system is too big it wont run long enough to remove the humidity. Learned this the hard way wyen i lived in ga and got a "deal" on a 4 ton commercial unit from a buddy.

Mini-splits have the ability to run at way less than full capacity, like 30% of full capacity. They make it really hard to mess up

Obviously they will run most efficiently when they are at/near full load design specs. The calculators I used for the proposed design all came up with around 1.6 tons and 2 tons is the next standard size - Having a little excess capacity is not bad when the weather gets extreme

I would think 4 units is a little crazy.

The variable capacity capability allows you to use the system only where you need it. More units = more control over the areas you heat or cool. Good stuff if it's in the budget

[Dave Sparks]

If money is not an issue well sure install 4 split systems in a 1200 square foot home. A great source for spare parts!  I probably would install one and get a new truck like Glens

[Rob_O]

If money is not an issue well sure install 4 split systems in a 1200 square foot home. A great source for spare parts!  I probably would install one and get a new truck like Glens

Mitsubishi makes a 4 ton, 8 zone system. I'm sure you could buy a nice used truck for what that system costs