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Community and Q&A

Mini split head placement

DavidAtAshby | Posted in Mechanicals on

I want to put a 24,000 BTU mini split into a single story structure that measures about 36 X 24. It is divided into one long space and three bedrooms across the back. I know I won’t get anything into the BRs without open doors but the simplest location is on one of the narrow end walls in the main area. My question is whether the unit will adequately condition the whole space or if the localized feedback from the one end will control temps and the far end won’t get cool. Or is it small enough that with the air movement I don’t need to worry? The alternative is an inside wall which is more central but more trouble for routing connector pipes. 8′ ceilings, moderately insulated, some large southern exposure windows but shaded by trees and overhanging eave.

It’s actually a summer home but the mini heat will be a real bonus in the spring and fall as a back up to the wood stove.

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  1. STEPHEN SHEEHY | | #1

    I think it largely depends on the building envelope. In a tight, well insulated house , you'll get pretty even distribution of heat. The great room in my house is more or less the size of your space and a single nominal 12000 btu minisplit (Fujitsu 12RLS3h) heats it pretty evenly. The unit is in a corner and not only heats and cools the space in front of it, but also the kitchen area which is open but behind the minisplit. It also heats/ cools the office/ guest room as long as we leave the door open.
    We're in Maine, house is very well insulated and met passivehauz air tightness.

  2. Expert Member
    Dana Dorsett | | #2

    The closer you can place it to the bedrooms the better it will be at actually getting some air flow into those open doors in the bedrooms. I have a relative heating & cooling a similar sized house with a 1.5 ton Mitsubishi. It's a bit narrower and a bit longer, but comparable square feet. The master bedroom & master bath are at one end, the ductless head maybe 12-15' from the other end, but blowing across the short dimension, not directly at the bedroom door. She's fine in the bedroom with the door open down to about 30F or so outdoors, but at 20F & cooler the bedroom needs a bit of space heater to stay comfortable during the heating season.

    But in cooling mode it's completely fine, in part due to the fairly low cooling load of the bedroom & bath. The only bedroom windows face north, the small bathroom window faces east, so there isn't a lot of solar gain to counter.

    A 2 ton mini-split for less than 900 square feet of conditioned space would usually be extreme overkill, with more than a 2x oversizing factor. Most houses that size (even without much insulation) would do fine with a 1-ton for cooling. Have you run any kind of load calculations on this place? (Try, if you don't have access to better tools. It'll oversize the load numbers too, but not by 2x. Be aggressive on the assumptions regarding shading factors.)

    If oversized to the point that the mini-split doesn't modulate, only cycles, it's humidity handling capacity falls off a cliff.
    That's still true even if you run it in "DRY" or "DEHUMIDIFY" mode. That may not matter if you are in a location where the summertime dew points never break out of the 50s F, but it matters quite a bit in locations where outdoor dew points hang in the 70s for a week or more at a time.

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