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Community and Q&A

Ductless vs. Ducted Minisplit for Bedrooms

casadelsoul | Posted in General Questions on

My house in Nova Scotia is roughly 200 years old and currently quite drafty. An energy audit h tells us that insulation is pretty good, but air leakage is our biggest problem. We are planning to seal up as much as we can ourselves and then have the AeroBarrier process done while we are doing a kitchen and bathroom renovation.

My dilemma is this:

We are having heat pumps installed to drastically reduce the usage of a 20 year old oil fired hydronic system and to cut back on wood we burn in our Pacific Energy wood stove. We are also looking for cooling and dehumidifying in the summers. The house is roughly 1800 square feet but the layout presents some challenges.

I am leaning towards Daikin Cold Climate equipment because of the warranty but not fully decided yet. Still looking for the right installer after speaking with many.

The one istaller I like so far has suggested a condenser on either end of the house with heads shown in red on the floor plan. I think these make sense, but I am concerned they may be oversized.

The REAL issue is the upstairs bedrooms off the hallway. The largest room off to the sdie upstairs is the master and the other rooms are kids rooms, office bathroom and laundry. Laundry is off the master. I have been advised to put a ducted mini split in the unconditioned attic (or insulating the attic which i do not want to do at all) I think we could get away with one head in the upstairs hallway if we leave the room doors open most of the time which we already do.

Can anyone provide any insight or advice on this situation?

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  1. exeric | | #1

    Ductless mini splits for non-dedicated room spaces usually need a fairly open floor plan to work. For instance, a single ductless mini split works well when it is on an exterior wall in a generous sized room and which points to bedrooms/bathrooms that all have entrances on the opposing wall. In that case any air blowing will naturally tend to fill the spaces adjoining the opposite wall. When you use a formal hallway to move air and there are rooms adjoining midway in the hallway I think those rooms probably won't get conditioned adequately. That's my intuition, for whatever that's worth.

    Basically, just think of air molecules like you would think of a weightless astronaut in a spaceship pushing himself off of one wall and trying to get to another room in the ship. It helps a lot if the entrance to that other room is parallel with the wall you launched yourself from and at the end of the corridor in the ship. You'll just sail on by other room entrances on the corridor that you're passing through. So, I would say for your house your HVAC guy has a good point in his thinking.

    1. casadelsoul | | #4

      Any thoughts on a ceiling cassette with 4 way blowers pointed at the bedrooms? I know I'm probably grasping at straws, but the expense of this setup plus the cost of building an insulated space in the attic is $30,000 CAD or more.

      1. exeric | | #5

        The problem might be in getting the air to the master bedroom since it wouldn't be adjacent to the hall. That's assuming the ceiling cassette is located in the hallway. I don't have personal experience with that type of set up since I'm a DIYer type of person. Others here will have experience with that or can possibly come up with a situation where a ductless can work. Sometimes you can design a simple minimalist ductless system for an entire floor after the house already exists and sometimes it's difficult. That's where luck comes in. Often you just need to be lucky or else add an additional mini split for the master bedroom

  2. user-5946022 | | #2

    1. You may have difficulty sizing the load (sizing the unit) before you finish air sealing. You may be able to run an energy model using your current usage, with a guess at your infiltration, then revise to a set infiltration, which should lower your load. You might be able to get the aerobarrier people to agree to meet a particular ach/50 number. Otherwise wait until after to install the unit?
    2. have you considered a ducted system installed either in the ceiling of the hall and drop the ceiling, with some soffits along one side of the shared bedroom walls or installed in attic and build a small enclosure around it and the ducts in the attic?
    3. Biggest consideration is if you can find someone to service the thing when inevitably it needs service. What will you do if that one contractor is out of business?

    1. casadelsoul | | #3

      1. Yes Aerobarrier are able to control the ACH/50 in real time as the process is happening and we are aiming for between 3-5.
      2. It may be easier to just build ta small insulated space for the unit in the attic than trying to drop the ceiling and build it in that way.
      3. I am fairly confident the installer will be around for a while but there is never any guarantee I suppose.

      Any thoughts on a ceiling cassette with four direction air in the hallway with the blowers pointing at the bedrooms?

      1. user-5946022 | | #8

        I think you will be happier with a ducted system than with the ceiling cassette. And FAR better resale value in case that is any consideration. I think a cassette with a four way blower would negatively affect resale.

  3. ohioandy | | #6

    Of all the factors in a minisplit decision, I'd agree that the most important is finding a supplier/contractor that you trust and can be present if issues develop. That said, the main problem with minisplits today is contractors' lack of imagination. These machines are fantastically capable and versatile, but the typical proposal from HVAC people is to hang a bunch of oversized ductless units on the walls and be done with it. Your room layout is not atypical of old houses, and it's not suited to this strategy.

    Here's a few alternate ideas. I know you're leaning towards an attic installation, but without knowing the particulars it still seems like a dropped hallway ceiling, or even just a dropped section, is the easiest solution for a 9K ducted unit feeding the four bedrooms. A ceiling cassette works, but only as long as doors are open. Some makers allow vertical mounting of the ducted unit (Fujitsu, for one) which can be mounted in a side wall with a wide but shallow duct going up and over. Why not also put a 12 or 15K ducted unit into the ceiling of the downstairs great room, with supplies pointing down AND up to also handle the big room upstairs? All of these short little duct runs allow you to zone out your house with quite a bit of control, using manual dampered registers.

    Not sure you'll find a contractor willing to do these kinds of installs, but could you DIY that part and find one willing to just do the commissioning?

    The downstairs room is a tough one. Even a 9K would be way oversize for that space. How about just baseboard resistance heat in there?

  4. monkeyman9 | | #7

    I had a choice very similar to what you're making now. My layout has some similarities.
    Basically 4 rooms on corners plus a large barhroom. I knew I would never be happy with a head in the hallway and leaving the doors open all the time. That's exactly what I did downstairs and it works perfectly with the doors open there.

    With that closet that you have in the middle by the stairs, I would put the ducted mini split inside that room on the wall. Run the ducts you can to the rooms near. Then run the remaining ducts between attic joists or as close above as you can. Hard duct it and spray foam the ducts. Then mound insulation over them. You'll never seal the ducted mini split perfectly, you don't want to coat it with spray foam, and you don't want that in a hot/cold attic, so it's best to keep that within the building envelope. I finished my project before summer and it's operated great since. My attic is unconditioned as well. Can't say I've hit a heating season yet. In in Massachusetts. I ran all the calcs and so far it's worked out as planned. Make sure you oversize the ducts.

    For the returns you can use jumper ducts through the walls or in the Attic to the hallway. Make sure you upsize the return ducts. Go with as large oversized filter as you can to keep the static pressure down. I managed to squeeze a 20x25x5 in.

    1. user-5946022 | | #9

      This sound like good advice

    2. monkeyman9 | | #10

      If you want any pictures or have any questions, let me know.

    3. exeric | | #11

      I've thought about Monkeyman's reply, and I think his idea is a good one. At some point you just have to give up being half assed in a solution to a problem. Now the OP just has to find an HVAC guy that he can sell on this idea. Monkeyman's plan is good because it doesn't require a conditioned attic.

      The devil, or god, is in the details though. The ducting in the attic, for those places you can't make a raceway in conditioned space, have to be sealed and insulated well with CCspf. Otherwise, cool air in summer will condense on it and create a waterlogged nightmare in the cellulose on the attic floor. Also, all penetrations into the attic have to be very well sealed, probably with CCspf, for the same reason. It will be a lot of tedious detail work so make sure you can get a conscientious contractor to do it. That may not be so easy.

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