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one mini split for entire floor....

We have central AC that's twenty years old and I was wondering if instead we could get away with a one-ton minisplit on each floor. Assuming that the one-ton matches the overall load is it possible for one unit to reach, let's say three small to average size bedrooms from the ceiling of the hall that connects all three? Obviously not as well as having a supply register in each room but is it remotely doable? (current AC handler and ducts are stuck in very hot summer attic.) our AC t-stat is set for no lower than 76 degrees.


  • Eugene Silberstein_2
    Eugene Silberstein_2 Member Posts: 349
    My vote would be no.

    In order for the cooler, conditioned air to "reach" the rooms, there needs to be a difference in pressure. If the indoor unit will be located in the hallway, the lowest (air) pressure will be at the unit's return (in the hallway), while the highest pressure will be at the supply (also in the hallway). With bedroom doors closed, the desired airflow path will be from the supply, right back to the return.

    Even with the doors open, the airflow will likely be insufficient to actually cool the rooms without overcooling the hallway.

    If it were my house, I would steer clear.

    Please let us know what you decide..
  • don_9
    don_9 Member Posts: 395
    edited April 2012
    Duct work in attic

    The duct work being in the attic although not the best place for it you still could seal all joints with mastic and wrap it in r8 foil insulation and reduce the conduction.

    We have test the temp at the airhandler in then to end of the duct and found when using insulation with a r valve at or better then r8 that the heat gain from the attic to the duct is not too bad at all.Sure it would be better to be in the condition area and even a condition attic for that matter but you have to work with the house you have.

    The bad thing about using ductless split on old homes is the exterior can look like a storage shed for down spouts.Unless you are willing to open up some inside walls.

    Good luck with the upgrade on the hvac and if high seer is what you are looking for nordyne has a 23 seer iq drive split system.

  • D107
    D107 Member Posts: 1,814

    Thanks for the informative replies. I had a feeling what the answer would be, but with Mr. Silberstein's air pressure explanation and Don's thoughts it's pretty clear it won't work. I agree with the mini-split 'downspout' festival idea. We were in Istanbul a few years ago and so many apartment buildings had cables and compressors on the outside walls.

    We had hoped to bury the ducts in the attic floor, but creating a conditioned space has other ramifications with building code in terms of occupiable/habitable space, so until we resolve that we'll have to stay with what we have.

    I have looked into the Daikin Altherma Air Source Heat pump system, can't find installers near me, but that's a very intriguing system. As we are in the middle of some other big house projects and both our AC and heating systems are working pretty well, we'll kick that can down the road a bit. The idea of removing heating combustion from the home is very attractive to us.
  • EddieG
    EddieG Member Posts: 150

    Look at Fujitsu's HFI system. They offer different types of indoor units, up to 9. Such as ducted type, which could take care of multiple rooms with one unit. You could also use wall units as well. You could also get away with one lineset between the outdoor unit and house, which means 1 downspout possibly. Don't get me wrong the Altherma is a great product, but if you don't have a local installer?
  • Jack
    Jack Member Posts: 1,046
    Yes, you can...

    I've had a lot of experience doing this in the heat side. The key is to "allow" the air to circulate. You will end up with a 2-3* differential in the spaces. Cut a register over the door or in the corner of the bedroom high up in the corner and short cut the door to allow some convective air movement. These units are variable speed and with the longer run times will project the air into adjoining spaces much better than the old single stage equipment.

    The post on the HFI system is correct as well. There was discussion of Fujitsu allowing the Concealed Ceiling Evaporators to be able to connect to a single condenser. I don't know if they did this this year. Static pressure capabilities are very low so duct work must be spot on. With proper location of the evap you could cover all three bedrooms with one evap.

    Your other option for getting air into a room is to check out the Tjernlund Airshare. It is specifically designed for this purpose and does an excellent job.
  • Techman
    Techman Member Posts: 2,144
    One mini

    Don't do it. Putting in air openings in walls inbetween rooms lets more than air go from room to room.I think its called "privacy".
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