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Community and Q&A

Minisplit choices

Richard Jackman | Posted in Mechanicals on

I am looking to replace window ACs with split units but am running up against a common problem – multiple small rooms that each need their own cooling, but using individual heads will result in excessive cooling capacity and the problems it brings with it.. 3 small (2x 10×12, 1x 10×20) bedrooms, living room , and EI K all need cooling. Metro NYC area.

House is a 1200sq/f semi-splanch (1932 bungalow with 1966 addition). New windows, decent insulation and will be adding 1″ rigid foam board when new siding goes on in the fall. Extensive air sealing has been done but have no measured tests except cutting heating bill over 60% (gas HW / baseboard). Last two summers have been able to cool the entire house reasonably on the hottest days with a single 10.5 K window shaker and box fans to move air around. There is a 9 K minisplit in the MBR, oversized to the point of poor humidity control at temp setpoint.

Considering a single ducted 18 K minisplit that can scale back to 8 K but it would have to go in unconditiioned attic space. Part of that choice is the poor esthetics of wall-mounted units in every room.

My concern on attic install is no shade and even with good ventilation the attic can easily get to 100°F ambient.

Is a ducted minisplit the right way to go or is there a better option?

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  1. GBA Editor
    Martin Holladay | | #1

    The standard solution to your dilemma is to install a ducted minisplit unit. If the ducted unit has to go in an unconditioned attic, you should at a minimum make sure that your ducts are well sealed and well insulated, and you should consider the option of creating an unvented conditioned attic -- especially if your existing attic insulation is sub-standard.

    If you don't want to incur the expense of creating an unvented conditioned attic, at least beef up the insulation on the attic floor to R-49 or more.

  2. D Dorsett | | #2

    BTW: The -18RLFCD ducted mini-split can modulate down to 3100 BTU/hr in both heating & cooling mode (which is quite a bit lower than 8K):

  3. Richard Jackman | | #3

    Thanks for confirming my suspicion. Ceiling joists are are a mix of 2x6 (1932 section) and 2x8 (1966 section). Both are joist areas are filled with fiberglass batts but there is limited headroom - center is ~3.5' - not sure how I'd ever get to an R-49 up there.

    Much as I don't like wall units going ducted we loose the ability to control by zone - we often only cool one or two BR's and only at night. Is there a version of the 18RLFCD that can run 4 heads? Modulation down to 3k would let us run a single head if needed.

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