GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Ducted vs. wall-mounted minisplit system

Rahm | Posted in Mechanicals on


I’m planning to add a mini-split system to my house in New York’s Hudson Valley. I want to heat and cool three upstairs bedrooms with the system. Two of the bedrooms are relatively small and on the north side of the house while the other bedroom is larger with southern exposure. All three rooms have cathedral ceilings. There is a hallway and bathroom between the three rooms with attic above. I’m considering 3 different configurations, all three configurations would use a single outdoor unit.

Option 1: One wall mounted unit in each bedroom.

Option 2: One ducted unit in the attic space with supply ducts to each bedroom and a single return in the hallway.

Option 3: One wall mounted unit in the larger bedroom and one ducted unit in the attic for the two smaller bedrooms.

Using a separate unit in each bedroom would give me the most control but it would also be the most expensive. The wall mounted units aren’t terrible looking but an advantage of the ducted unit is not having to see the wall units.

In the winter we run our woodstove often and the hall at the top of the stairs gets quite warm. I like the idea of using the ducted unit in fan only operation to distribute that heat to the three bedrooms.

I would love to use the ducted unit for all three bedrooms but I’m afraid that it could be hard to keep the temperature comfortable in all three rooms. Any thoughts or advice would be great.


GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Yupster | | #1

    You have to have your Manual J heat loss/gain before any equipment selection can begin. Then, you will discover that your loads are too small to be served by multiple minisplits, installing more than one for a few small rooms will greatly reduce the efficiencies of the units and reduce the comfort level supplied by them. If you have your ductwork for a ducted minisplit designed by a competent hvac designer (usually not your contractor) then it will supply the right amount of heat/cool to maintain comfortable temperatures in all three rooms without any trouble.

    It seems questions like yours regarding how many minisplits get posted every other day on here. I blame manufacturers for bad marketing that shows these units as single room solutions. You will find the answer to your questions very much the same as the others, so if you search the archives for questions and articles regarding minisplits you will find further and more detailed answers to your questions.

  2. Rahm | | #2

    Thanks Yupster,

    Do you think I'll have trouble regulating the temperature in the different rooms as the needs change due to different amounts of southern exposure and heat from the woodstove effecting some rooms more than others?

  3. Yupster | | #3

    I think the ducted mini-split running in fan-only mode would help distribute the heat from the woodstove. But woodstoves are not well suited to distributed heat. Temperature differences are inherent with heating with a woodstove and there aren't many ways to eliminate that without getting expensive and fancy. As far as temperature goes regulation goes, the ducts will be sized and balanced to introduce enough cooled air to maintain the temperature on the hottest day of the year. If you have a LOT of glazing in the one room facing south and not very much in the others, there is a possibility the other rooms will get colder while the minisplit tries to maintain the setpoint in the room with lots of glazing, assuming that's where the thermostat is. How bad the it would be can't be known over the internet but a Manual J calculation would give you an idea how different the loads are. I think you will find the differences in temperature acceptable and if they are not, source control is better than trying to microzone. So maybe put up some blinds, plant a strategically placed tree, when replacing windows get a low solar heat gain window, or build an eyebrow over the glazing that is letting in too much sun.

  4. Expert Member
    Dana Dorsett | | #4

    In most insulated homes with double pane windows bedrooms tend to have heat loads in the 1500-2500 range @ 0F outdoors, 68F indoors, with many exceptions to prove the rule. Hudson valley 99% outside design temps are mostly in positive digits territory, but Albany's is -2F. (see: )

    If the 99% design heat load of a room is less than 3000 BTU/hr a half ton head on a multi-split system would be oversized to the point that it would lose efficiency. So the odds are the head-per-room approach is going to be more expensive and less efficient than a ducted solution.

    A 3/4 ton mini-duct on a multi-split compressor serving three or four sub-3K load rooms would be more efficient, as long as the ducts and cassette are inside of conditioned space, not in an attic above the insulation. More efficient still would be a modulating mini-duct cassette on a dedicated compressor, not a multi-zone compressor.

    So start by doing some room-by-room heat load analysis, see what it all adds up to. Then think about where you might be able to sneak in a mini-duct cassette just below the ceiling level ( say the top of a closet or something) and where you might be able to build in soffits to accommodate ducts fully inside the pressure & insulation boundary of the house. Fujitsu's mini-duct units have the flexibility of begin able to mount them vertically (in the side of a closet or something), and also have more capacity & higher efficiency at 0F than most of the competition.

    Without load numbers and a sketch of the floor plan it's too early to say for sure, but that's probably the direction that makes the most sense. A 3/4 ton 9RLFCD mini-duct cassette on a dedicated compressor can deliver as much as 15,000 BTU/hr @ +5F, an as much as 13,500 BTU/hr @ -5F, but will still throttle back to as little as 3100 BTU/hr @ 47F, which is a better than average modulation range, and WAY better low-temp capacity. (They have 1 ton and 1.5 ton versions too if that's not enough.)

    Using air handlers to distribute heat is very inefficient when the temperature differences are small. Moving 75F air into a 68F room uses many times the cfm to deliver the same heat rate using 115F air.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |