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Community and Q&A

Minisplit sizing and location ideas

gozags | Posted in Energy Efficiency and Durability on

I will soon break ground on a garage/adu project. For simplicity sake, the construction will be moderately simple. 2×6 framing, ply sheathing (taped seams), Rockwool insulation. Extra attention will be paid to air sealing, drywall details, etc. Raised heal scissor trusses, vented roof, cellulose insulation. No can lights, minimal ceiling penetrations.

Garage is 710sqft, ADU is the same but the interior stairs are not going to be counted towards the ADU’s max size of 600sqft (city allowance).

The garage itself just needs to remain temperate. 60’s in the winter, 75 in the summer. Zone 5 (Spokane, WA – it was 112 at times this year…).

The ADU will be all electric (solar is an option, exploring that). Bathroom will have heated floors and accessory wall heater. Bedroom will most likely have accessory wall heater but my goal is to heat and cool the whole space with one minisplit in the garage and one in the ADU.

Primary concern is the bedroom cooling and heating. It will be a rental and who knows how the occupant(s) will manage the bedroom door situation, open or closed, etc.

I will have help from a semi-retired HVAC guy that has experience with minisplits and can assist me with the line set brazing, flaring and refrigerant needs. I am thinking Midea hyper heat models for the ADU and whatever 9 or 12k unit is priced right for the garage since the needs there are way less.

Single head location in the ADU: above the couch in the living area or perhaps on the short wall just outside the bedroom door?

I am not opposed to a ducted split system, thinking that perhaps I can maintain access to the mechanicals of such a system from the garage below.

Any suggestions?

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  1. Expert Member
    AKOS TOTH | | #1

    You generally want the wall mount on an exterior wall. I would put it beside the juliet on the kitchen side.

    If you put in heated floor for the bathroom, you won't need panel heater. Make sure to install the temperature sensor of the thermostat in a length of pipe (5/16" pex is perfect for this) so it can be esaly replaced down the road.

    A panel heater will be needed for the bedroom.

    A ducted unit is definitely possible since you have tall ceilings. Might be worth it as they are less maintaince and than you can skip the electric heat in the bath+bed. Won't pay for the install cost difference but will help.

    For the garage, get an oversized budget mini split with a pan heater. You want something that can heat/cool the place quickly when needed. Something like this, although for a couple of extra bucks you can get a Midea hyper heat.!/product/30906

    1. gozags | | #2

      Thanks for the suggestions Akos.

      The more I look at it, the more sense it makes to put a ducted unit in the hall closet, on the floor with the return pointing out into the living area by the bedroom door. We''ll be using 12" i-joists, 16oc for the flooring system and I can bring the plenum down into the joists and go north/south and come up in the two walls to feed everything. I have some play in the wall positions and the closets - so we can probably build up something that allows for the ducted unit to be accessible.

      The kitchen/bath side is facing south and the west gable end is where any outdoor units will reside. The north side is on an alley, so I have just enough room for a walkway to the man door for the ADU. Makes putting a head unit on the east gable end a bit more complicated.

      1. Expert Member
        AKOS TOTH | | #3

        With a garage bellow, it might be better to keep the ducting inside the ADU, although if you seal the ceiling bellow well, it should be less of an issue.

        You could also go up from the closet there and run the plenum across the ceiling in a small bulkhead just bellow the peak. This would let you get more flow to the perimeter of the room which is generally better for comfort.

        Some of the slim ducted units (Fujitsu and Midea/Carrier) can mounted vertically so they won't take up all that much space in the closet. Some of the units have a front duct adapter as an accessory which makes plumbing these up much easier.

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