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HVAC sweating condensate

cbut8995 | Posted in General Questions on
1 1 Ducted w/ Linear Slot Diffusers SE-KD09NAH Bedroom with base pan heater & hyper heat
1 2 Ducted w/ Linear Slot Diffusers PEAD-A12AA7 & SUZ-KA12NAHZ Living Room, Basement with base pan heater & hyper heat

0Hi All,

Was going to get the following mitsubishi duct units with the modern linear slot diffusers. My GC says the following:

  1. Line diffuser (tapeable) require constant air temperature in the unit, otherwise it will start sweating condensate if there’s any outdoor (humid) air exposure.”

Was wondering if anyone had opinions on this as I love the modern slim look of 1 single slot and its hidden unlike the wall mount units. I do not want any sweating condensate as water anywhere is bad especially within the walls. I live in NYC and we would have 3 of these units in total. 1 bedroom, 1 living room, and 1 basement area. 

If this is true are there any alternates people suggest that can still achieve that modern recessed look from a linear slot diffuser. This was going to be used for heat and cooling and had hyperheat and base pan heater. 

Thanks in advance.

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  1. Expert Member
    Akos | | #1

    Mini splits are generally modulating units which means even temperature output. Assuming those units are sized for the load and the heads are not cycling, there will be very little temperature variation (with 3 heads in a 1 bed place, this feels hugely oversized)

    The only time I've had issues with registers sweating is from construction moisture while running the unit in dry mode after drywall taping.

    You do have to do accurate sizing on the grills as these tend to be restrictive, you want to make sure that you are not choking the air handler.

    1. cbut8995 | | #4

      Is there a calculation you recommend. I am planning on using the width of the room linear slot diffusers. So for example the bedroom will have a 1 opening 10 foot long slot diffuser, the living room and bedroom will each have about a 15-20 foot one.

  2. Expert Member
    Dana Dorsett | | #2

    >"...with 3 heads in a 1 bed place, this feels hugely oversized..."

    +1 !!

    Unless this is a penthouse suite sized NYC apartment the 1% & 99% design loads for the entire apartment is likely to fall within the capacity of a SINGLE -KD09 (or maybe a single KD12).

    All but the leakiest, largest, and/or uninsulated basements would do just fine with a single FS06 (half ton) high wall coil. Even the minimum cooling & heating output of a KD09 could be higher than the design loads of a <1000 square foot basement- a modulating system so oversized that that rarely or never actually modulates.

    A pair of KA12s could heat my entire (none too efficient sub-code antique) 2400' house + 1600' of
    insulated basement at NYC design temps.

    Manual-J, anyone?

    1. cbut8995 | | #3

      Hi Dana,

      I agree but there was no other way to get the look for the linear slot diffusers and have each room have its own temperature. It is a more expensive apt with high ceilings and a lot of 8 foot tall windows that are all operable.

      The other units I am using a 9k btu that modulates down to 1700btu but I am living in the large 1 bedroom unit and wanted this more modern look with each room having its own control temp

      1. Expert Member
        Akos | | #5

        If you look at the blower curve of the PEAD-A12AA7, the flow rate through the unit doesn't change a lot from a bit of pressure change.

        This lets you do a bit of simple zoning with just a motorized damper driven by a stand alone thermostat without any fancy controls.

        The idea is to over provision a smaller zone with say 120% of the flow rate it needs and adjust the damper's closed position to provide 70% of flow. The air handler will have no problems with modulating around this bit of pressure and flow change.

        This does require a bit of design as you have to get precise flow rates and heat and cooling loads for each area. Better chance of this working than figuring out how to run a place with sub one ton of heat and cooling load with 3 tons of equipment.

        1. cbut8995 | | #6

          Most of the duct units wont really have much duct run from the indoor unit to the linear slot diffuser. Does this make any difference? most of the units will be very close to the indoor unit. Is it better to have a long linear slot over 8 feet single opening like this and some being over 15 feet . basically bigger the better and I wont have condensate? Its an apt on the first floor and the basement too.

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