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Community and Q&A

Minisplit shared between a bedroom and bathroom

Chris D | Posted in Mechanicals on

My house has a small second story, sized about 1/3 of the total house. It contains the master bedroom, master bath, and a wedge of unconditioned sub-height attic storage (knee wall!).  440 sqft total, with maybe 75 sqft of that for the approx 8’x9′ bathroom.  Flat 8′ bath ceiling, with a 10 foot semi-cathedral in the bedroom under the rafter ties.

Currently the second floor return and supply ducting travels from the crawlspace to the unconditioned attic through a chase, then to the unconditioned space within the rafter ties.  All of that mess is getting ripped out, and the plan is to do a minisplit upstairs to provide a standalone zone, and likely a split system for the 1400 sqft first floor.

I’ve been brainstorming choices for minisplit configs for a while, and as far as I can figure, there are 3 options:

1) Wall-mount minisplit in the bedroom, and let the bathroom sort itself out through the open bathroom door.  I have no idea how practical that is, with showers and occasional door closing.  Could add a large grill on the wall or above the door, if needed for air exchange.  Also considering a Mitsubishi MLZ, which has some of the same easy-install advantages.

2) Make a soffit for a low-static ducted unit, and figure out a way to divert a little air from the outlet through the bathroom wall.  Intake vertically into the soffit bottom, exit horizontally close to the ceiling.  Fairly simple, except for air diversion into the bathroom.

2) Ceiling cassette with a branch duct. I would need to insulate above the cassette, and would not have any service access from above once installed (between rafter ties).  Could likely snake a branch duct between the two attic spaces to feed the bathroom, then would need to bury the duct in insulation.

Are any or all of these concepts completely harebrained?  Option 1 is obviously the simplest, but also the one I am most skeptical of, if it leaves an orphaned room without enough flow.

Edited: I’m Climate Zone 3A, Charlotte NC area.

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Replies

  1. Expert Member
    Malcolm Taylor | | #1

    Chris,

    Where are you? Here in mild Southern BC I don't have to add any heat to my bathrooms, but I bet that's rare for most climates. If it's a marginal case, why not go with Option 1, and add a small resistance heater than can be used for the few days it is needed, and removed for the rest of the year?
    https://www.convectair.ca/en/products/120v-plugin/apero

    1. Chris D | | #3

      I always have to leave off a few important details, just to make it interesting (or confusing?).

      We're Climate Zone 3A, in southern North Carolina, so are cooling dominant. It was 96degF here today, for example.

  2. Charlie Sullivan | | #2

    I think you'll be fine with option 1, especially if you mount it near the bathroom door.

    1. Chris D | | #4

      That's what I'm wondering; it would make things rather easy compared to the ceiling cassette or low static options. There's already not a lot of thermal input from the sad little wallstack duct in that room, which would bolster that case.

      When you say "near", would that involve direct airflow toward that bathroom doorway, or just the proximity of the unit? I have a few options for mounting locations if it's going to be a simple wall mount head, so there's a bit of flexibility there.

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