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Will a Fujitsu RLS3H Ductless Mini Split Heat Pump be enough?

darejobachjo | Posted in GBA Pro Help on

I have been struggling about what type of heating system to put in our home. Ever since I read about the Fujitsu and its 33 Seer efficient system, I have wanted to install 2 in our home, one up and one down. Our home was built originally as a mountain summer cabin with baseboard heating and no duct work. It is in Western North Carolina, elevation 3600 feet.

The first floor is a finished basement made of 8 inch concrete block built on a poured concrete slab foundation that is semi earth-beamed on 2 sides with natural stone veneer on the above ground walls that was quarried locally.

The main room in the center of the downstairs is the Den with a fireplace insert which we use when the power is out. The Den is 376 sq ft which includes a small bath at one end of the room. A 144 sq ft bedroom room is adjacent to the den off the left side as well as a 96 sq ft laundry room adjacent to the den off the left side.
A 225 sq ft bedroom is adjacent to the den off the right side. If I put a Fujitsu RLS3H Ductless Mini Split Heat Pump in the Den, will that be enough if we keep the bedroom doors open (standard size bedroom doors)? If so what size?

The upstairs is stick built, 4 inch walls on half the house and 6 inch walls on the rest with added blown in insulation in the attic and a new metal roof. (built in 2 phases) The main room is the living/dining/kitchen at 668 sq ft. All together that space, including a 168 sq ft foyer is 836 sq ft. (the foyer is open to the living room with 6 foot french doors. It can be closed off from the main living area when an away room is needed) A 156 sq ft bedroom is adjacent to the living room. It has a private 5 x 7 bath. Another 5×5 half bath is off the living room. Can I put a Fujitsu RLS3H Ductless Mini Split Heat Pump in the living/kitchen and if so what size?

The entire house has a total square feet of 2144 including closets, stairs and all.

Any and all help would be greatly appreciated. Thank you so much.

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  1. GBA Editor
    Martin Holladay | | #1

    You haven't provided us enough information to answer your question.

    We don't know if your basement walls are insulated. We don't know if your house is leaky or tight. We don't know the size of your windows. We don't know if you have old double-glazed windows or high-quality triple-glazed windows. We don't even know the thickness of your roof or attic insulation.

    You can't design a heating system or a cooling system until you perform a heating load calculation and a cooling load calculation. Load calculations are Step One.

    Here are links to four articles to give you more information on the topic:

    Saving Energy With Manual J and Manual D

    How to Perform a Heat-Loss Calculation — Part 1

    How to Perform a Heat-Loss Calculation — Part 2

    Calculating Cooling Loads

    -- Martin Holladay

  2. darejobachjo | | #2

    The basement is 8 inch block, not poured. The above grade walls are insulated with 1 inch blue foam core board with 3/4 inch pine tongue and groove. The walls are earth-bermed up to 4 feet on 2 sides. Below grade walls are not insulated. There are three 3 x 3 double pane replacement windows in the Den, one in the bath, one in the laundry room, and two in the smaller bedroom. There are two insulated Jeld-Wen 4 x 6 double hung windows in the larger bedroom. Attic is Rafters with 12 inch deep blown Cellulose insulation R 38. All windows on the main floor are premium vinyl clad, wood interior low e, argon, double glazed, Jeld-Wen double hung. Upstairs walls are R19.
    The home has two fireplaces with wood insert both in living room upstairs and in den downstairs. The windows are well-fitted, doors are weatherstripped. The outdoor design temperature for our area is 15 degrees. So the DeltaT is 55. I am not concerned with the units ability to cool, only its ability to heat. we have very nice summers here in the mountains and with all the windows open are rarely hot. The main advantage of a cooling system is to keep it dry in the basement in the summer, so as not to have too much moisture, to keep the mildew growth down, especially in the basement closets, even though they are lined with cedar.
    I hope this is enough information.

  3. GBA Editor
    Martin Holladay | | #3

    Q. "I hope this is enough information."

    A. Almost. Now that you have read my articles, put a pencil in the pencil sharpener, and get to work.

    If you don't want to do the work yourself, you should hire a HERS rater, mechanical engineer, or energy consultant to perform your Manual J calculations.

    -- Martin Holladay

  4. Expert Member
    Dana Dorsett | | #4

    The RLS3 comes in three different sizes but two of ANY of them will probably deliver way more than your 99% design heat load, but there's no telling how well it will heat the doored-off rooms (with doors open) without the room-by-room load calculations.

    If the other rooms heat reasonably with the wood burners, they should do just fine with appropriately sized mini-splits. The convective heat transfer between floors will be somewhat different, but mini-split blowers can be set up to throw far more heat down hallways and through doorways than a wood-burner will via convection alone.

    A reasonably tight ~2200 square foot house where half of it is insulated basement would usually come in under 25,000 BTU/hr @ +15F, but that's different from a earth-bermed house. If there's no insulation on the bermed earth sides it could be difficult to calculate accurately, but the loss rates would be pretty low on those walls, and wouldn't change much with the daily outdoor temperature swings, though it would change seasonally. Your load can easily be under 20,000 BTU/hr, or even under 15,000 BTU/hr, but without running the numbers you won't really know for sure. A single 9RLS3 (smallest of the line) can deliver 12,000 BTU/hr @ +17F, into a 70F room (HSPF test conditions) and would have about the same capacity @+15F into a 68F room. A pair of them could deliver 24,000 BTU/hr.

    Describe the wall stackups from the exterior paint to the interior paint, leaving out no layers. The descriptions above aren't clear- one description is 1" blue foam, another says R19. Is that 1" foam + R19, or just 1" foam? Or it 1" foam on 8" CMU (or other thickness)? There's no way to take a WAG at the U-factors of the walls without accurate descriptions.

    Elsewhere it's claimed that there is no insulation below grade. Are the CMU cores filled with concrete, or are they empty?

  5. darejobachjo | | #5

    exterior basement walls above 42 inches of earth on SE, SW sides: Dry Lock, 8 inch block (to my knowledge EMPTY), Dry Lock Blue foam board 1", 3/4 inch tongue and groove pine.

    exterior basement walls on NE, NW sides, No earth berm, same as above.

    bedrooms are on SW and NE sides of Den

    Upstairs SW, SE NW of half the house (older home): T1-11 siding, 2x4 studs with R19 insulation, wood paneling
    SE, NW, NE half of house (addition) T1-11 siding, 2x6 studs with R19 insulation, wood paneling

    the basement Den is so toasty warm with the wood heater it isn't even funny. The larger adjacent bedroom on the NE side, not so much. I was told by the fujitsu guy who came out to place a fan in the den and have it face the bedroom door.

    My other thought is because that is the one questionable room, imo, just put a gas vented fireplace on NE wall. end of stress.

    That leaves me with the question of size for the downstairs den unit. I am not worried about the smaller bedroom and utility room. They are partially earth-bermed and on the SW side of the house.

    Then there is the question of the upstairs unit and what size it should be to accommodate the 1000sqft of living space including the foyer and bedroom.

    thank you

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