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Q&A Spotlight

Putting the Duct Back in Ductless

A would-be HVAC designer wonders if a ductless minisplit head can be hidden in a closet and connected to conventional ductwork

A ductless minisplit head isn't everyone's cup of tea, at least not aesthetically. One reader wonders if he can still get the benefits of a ductless system if he hides the head and makes his own ducts.
Image Credit: Fujitsu

Ductless minisplits have a lot going for them. These high-performance air-source heat pumps operate efficiently at much lower outdoor temperatures than standard heat pumps, and they don’t suffer the same energy losses due to leaky ducts. A tight, well-insulated house may need only one or two wall-mounted heads to maintain comfort indoor conditions, in summer and winter.

It’s the “wall-mounted” part, however, that not everyone warms up to.

That is the case with Jerry Liebler’s wife — or “boss,” as Jerry introduces her in a recent Q&A post at Green Building Advisor.

Liebler is convinced a Mitsubishi Hyper Heating system would meet his heating and cooling needs. But the “boss dislikes the looks of minisplit indoor units.”

Liebler’s proposed solution is to place the head in a closet along with a small air handler and an outlet duct through the floor.

“A ‘shelf’ would run horizontally around the minisplit and the outlet duct of the air handler,” he writes. “With the closet door closed there would, in effect, be a ‘plenum’ above the shelf, pressurized by the air handler.”

Liebler thinks the air handler’s motor would overcome the friction losses of the duct work. Ducts through the closet floor would be connected to conventional ducts to distribute heated or cooled air.

“Has anyone done something similar?” he asks. “See any problems?”

That’s the topic for this Q&A Spotlight.

Have you thought of a ducted minisplit?

As GBA senior editor Martin Holladay points out, many manufacturers (including LG, Fujitsu, and Mitsubishi) make ducted minisplit systems.

“You don’t have to invent (and cobble together) your own ducted minisplit unit,” Holladay writes.

Yes, Liebler says, but none of them is capable of heating and cooling more than a couple of rooms, and…

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3 Comments

  1. Hobbit _ | | #1

    options
    Back when I was heat-pump shopping there was a *rumor* that
    Mitsubishi was going to have a central ducted vertical air-handler
    to mate up with their minisplit-oriented outdoor units. They
    don't seem to have gotten this quite together yet for the
    purely residential market but there *are* some ducted indoor
    units in the "city multi" line of stuff, in the PVFY series
    from about 1 ton and up, but your typical residential HVAC installer
    would probably look at you like you had two heads if you brought
    up the subject.

    Daikin, on the other hand, had the existing "inverter ducted"
    offering and despite being a rebranded Goodman indoor fancoil,
    appears to be a much more well-developed and integrated system
    aimed at the residential furnace-replacement market. That's
    exactly why I wound up with the system I have now.

    Mitsu and the others *really* need to get off their butts and
    compete for real in this market, because the easier it becomes to
    change out a forced-air furnace the more people will want to do it.

    _H*

  2. Aj Builder, Upstate NY Zone 6a | | #2

    more Daikin/Goodman info please
    Hobbit, do tell more about your exact install including some model numbers....

    Very interested....

  3. Dale Comeau | | #3

    Hire a Fujitsu Professional
    We are able, with the Fujitsu product, to address this concern in two ways that allow you to have an ultra high efficiency heat pump rated at 11.3 to 12.2 HSPF, depending on size you choose. You have the best of both worlds; hidden equipment and ductless efficiency.

    Solution one would be to mount Fujitsu's ARU air handler in the closet and use their Auto Louvre Grill http://portal.fujitsugeneral.com/doc_repository/454/Auto_Louver_Grille_Kit_Halcyon.pdf to make a clean, controlled entry into the room. Return air would be handled through a filter grill in the closet door. I would apply this setup only if the Auto Louvre is able to direct air into the main living area of the home. Being able to have an open and long throw area is very important.

    Alternately we would design a ducted system. http://portal.fujitsugeneral.com/doc_repository/454/RLFCD-RLFCC%20Brochure.pdf We have done many such design installs and have had absolute success. You of course don't have the fan power to manage a fully ducted plenum system so duct design is very critical. Done right, you'd think you had true central And the cost, efficiency and comfort is superior. In the case of a larger dwelling we simply utilize two or more air handlers. Now we have a fully zoned system!

    As far as output, efficiency at low temperatures and performance, you may have to make a disclaimer at times. Sometimes when given the option, a customer will opt to use their baseboard electric for two weeks in February to supplement rather than install that second system. Give them the info and let them decide.

    Oh yes: beware of Mitsubishi's claims of operation at super low temperatures. Yes they will work and yes the output is reduced. Get your professional installer to show you the engineering data to see what happens at -10 or -20 degC You may be surprised. If you are looking for a true heat pump heating system for all seasons, Mitsubishi can do it but Fujitsu does it better. In the frozen north it is very critical to understand where you will encounter your specific balance point.

    Be reasonable though. The days of designing a system for the just in case scenario are past. In you already have electric or wood then you are covered. If you have oil and want it gone you have more to think about.

    Dale

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