Ducted VS. Ductless Minisplits
We are in the selection process to replace a 25-year-old 80% gas furnace (supplemented with an electric heater in the second floor) as part of a basement remodel. This forum has been immenseley helpful as I’ve researched HVAC upgrades. I’m hoping I can get some input on my particular situation.
We are in Tacoma, WA (Zone 4 per the GBA climate zone map). The house is a 1-and-half-story Craftsman bungalow built in 1910. Construction is typical for the area and period—full basement with half the foundation wall extending above ground level, 2 x 4 construction, cedar siding, plaster-and-lath walls. Previous owners have replaced most of the single-pane double hung windows with vinyl double-paned, but the front façade still features the original single-pane glass (no storms). Another older remodel lightly finished the upstairs ½ floor, adding R11 to the central roof span and knee walls and closing off one end of the space. We have no insulation in the first floor walls.
We are replacing a 3.5 ton gas furnace and are looking at multi-zone mini-splits with ducted (first floor and new basement room for ~1110 sq ft) and ductless (upstairs ~650 sq ft.) zones. Heating is our primary concern, though we do currently use a window AC to cool the main floor for a few weeks a year. We’ve eliminated gas-furnace/AC combo and ductless-only solutions.
· Solution 1: Mitsubishi MXZ-4C36NAHZ outdoor unit (rated 36k BTUs cooling and 45k heating) with an SVZK24NA air handler (25K cooling / 25.7k heating) and two MFZ-KJ09NA (9k cooling / 11k heating) floor units for the second floor. The bid also includes replacing all duct work.
· Solution 2: Daikin RXTQ60TAVJU outdoor unit (57K cooling / 57k heating) FXTQ36TAVJUA air handler (36k cooling, 40k heating) and one FXAQ12PVJU wall unit (12k cooling 13/5k heating) for the upstairs. Bid did not recommend replacing all ducts.
I was a bit surprised at the sizing of the Mitsubishi outdoor unit and air handler since they are replacing a 3.5 ton furnace and condition an additional 750 sq ft of space. The bids for ductless and furnace solutions ran from 4.5 to 5 tons. My attempts at load calcs came in at 55.4 k heating (via loadcalc.net) and 42k-54k heating via highseer.com, though I’m the first to admit I could be way off.
My questions, for those of you who’ve made it this far: does the sizing of the Mitsubishi solution seem reasonable? Any experience with either Mitsubishi or Daikin ducted/ductless combinations you can share?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part