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Minisplit recommendations for small California casita?

Dan Burgoyne | Posted in Mechanicals on

I’m building a new 500 sq. ft. casita in Northern California (Sacramento). Very well insulated (R31 walls, R-56 roof). Summer cooling is needed, and some winter heat, but I’m also installing sealed, vented gas fireplace (more for aesthetics). I am considering a small 3/4 ton (9,000 Btu/h) ductless minisplit, and was wondering if there were any recommendations for a unit or system for such a space. I was looking at a Mitsubishi unit.

Evenings usually cool down in the Summer, and I have a lot of thermal mass, but feel cooling would still be needed for hot days. Also considering a small, natural gas, exterior tankless water heater, and would appreciate recommendations for that as well. 1-2 max occupants.

Thanks!

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Replies

  1. Expert Member
    Dana Dorsett | | #1

    The Fujitsu AOU-9RLS2 is a well evolved high efficiency design, as is the Mitsubishi MSZ-FH09NA (the follow-on to the also extremely solid FE09NA), and the Daikin FTXS09LVJU. It's hard to go wrong with any of those three.

    The Daikin is "only" rated for outdoor temps down to +5F (the others go sub-zero), but that doesn't mean it falls over and croaks at 0F- it's still putting out a lot of heat, but doesn't have a specified capacity below that temp. In your climate (and with your building envelope efficiency) that's not a show-stopper.

    When shopping for mini-splits the quality and ubiquity of local support is important- you don't want to have to call the LA satellite office only to be put on hold, or have to wait 30 days for repair parts to arrive from the factory in Kuala Lumpur. Tech support for the three above is pretty good in the US in general, but not at the same level in every location. If there are 25 certified installers and the distributor's training center within an hour's drive of your place is very different from an installer who is only in it as a sideline, with the nearest distribution center 500 miles away.

    At your insolation levels consider installing a heat pump hot water heater in a garage or attached shed rather than a gas-fired outdoor tankless, and orienting the roof lines for solar PV. At some point within the lifecycle of at mini-split or better-class heat pump water heater PV power is likely to become the cheapest form of energy out there on a lifecycle cost basis. Many analysts say that will be the case by 2030, some are saying before 2025, and leveraging it with heat pumps shrinks that time scale.

    The BTU output of even the smallest vented gas fireplaces are likely to roast you out of there pretty quickly despite the thermal mass of the building. Shop carefully- go for the lowest possible BTU/hr rating. At your R-values you may find yourself opening up windows even during the winter to dump excess solar gain. Think carefully about window size, type & orientation a well as overhangs & natural shading. Unshaded west facing windows can be a problem (even low-gain windows), unless you have exterior shades to kill that gain.

  2. Dan Burgoyne | | #2

    Thanks, Dana, I've read a lot about the Mitsubishi unit, but will check out the others as well. I am not familiar with heat pump water heaters, especially for such a small use, but will read up on them. I already have natural gas to the building, and I had understood that gas tankless were pretty efficient, and easily located right where its needed.

    Most of my openings are on the North and South ends, and I have very generous overhangs, and large trees on N,S,E sides. The gas fireplace is not necessary, and the ductless heat pump can easily provide what little heat may be needed, but it is for aesthetics, and can be dialed down pretty low.

    Thanks again for your advice.

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