Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Mitsubishi air handlers on same branch box unwanted heat.

I have 3 air handlers on the same branch box. With only 1 room thermostat calling for heat, the other 2 which are NOT calling for heat, because the their room set points are way below room temp, are warming up. This in turn warms up their rooms. I'm told the valves in the branch box when in the heat mode never close all the way. Is this normal?

Comments

  • GW
    GW Member Posts: 4,538
    Three air handlers on one box, curious. What size units? Small units I suspect 

    It’s expected to bypass some hot gas into idle zones. Are you saying the blower is pushing air? The blower should not be on. 

    How big are these rooms?

    curious, what controls are you using? MHK2? 
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
  • ahallasjr
    ahallasjr Member Posts: 4
    Gary, Here is a list of my equipment.

    MXZ-4C36NAHZ-U1 Heat Pump
    39,554 BTUs Cooling
    42,633 BTUs Heating
    19.1 SEER, 14 EER, 11.3 HSPF

    Branch Box 1 PAC-MKA32BC

    Living Room
    Wall-Mounted
    MSZ-GL12NA-U1 S/N
    11,718 BTUs Cooling
    14,273 BTUs Heating

    2nd Floor Suite
    Floor-Mounted
    MFZ-KJ09NA-U1 W/MHK2
    CONTROLLER INCLUDED.
    8,788 BTUs Cooling
    10,903 BTUs Heating

    3rd Floor Bedroom
    Floor-Mounted
    MFZ-KJ09NA-U1 W/MHK2.
    CONTROLLER INCLUDED
    8,788 BTUs Cooling
    10,903 BTUs Heating

    The 2nd and 3rd floor use MHK2's and provide heat even though the set points are far below the room temps. The fans are NOT running. The vanes are open and they are acting like radiators, causing unwanted heat.


  • ahallasjr
    ahallasjr Member Posts: 4
    Gary,

    Living Room. 550
    2nd 550
    3rd 300

    Approx.

  • GW
    GW Member Posts: 4,538
    Makes sense, when you said air handler I thought of something else.

    That’s a very routine installation.

    Multi zones will always shoot some hot gas/energy, especially when it’s not super cold outside.

    The smaller the room, the more noticeable this overshooting effect will be.

    The lowest capacity on that unit is roughly 30%, so, this time of year, it’s extremely hard for that outdoor unit two run a good healthy cycle and not create some excess energy.

    you have a 12 and two nines. your outdoor unit is a little bit on the big side.

    I always try to promote single zone systems. A lot of people don’t wanna have a number of units sitting outside their house. we have one house with 10 units sitting outside, and a month ago we did a house with eight units sitting outside. It’s a little busy, but similar zone systems are the best performance

    Gary 
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
  • ahallasjr
    ahallasjr Member Posts: 4
    Gary, I’m a novice, so thank you for sharing your expertise….