Adding minisplits to second floor of Cape Cod Style
I recently had a HVAC contractor come out and give me some options on my cape cod style house in suburban Philadelphia (Zone 4A). Currently there are no return ducts from the second floor and minimal supply ducts as well, leading to a noticeable temperature difference on the second floor. The house layout does not allow new duct work to be run to the second floor easily, so it would be expensive and probably still undersized.
The house layout is as follows: The second floor consists of 2 bedrooms on either side (roughly 12’x16’ each) and a bathroom in the middle all connected by a hallway and the stairs. Total second floor area is 500sf. The walls are R-15 and the ceiling is R-50 in the middle and R-17 in the slopes. The first floor total area is 1000sf (2 bedrooms, living room, and kitchen). The basement has R-25 on the walls and R-5 above the slab and is 800sf. The house is about equal to current code minimum tightness based on a blower door test.
The house currently has 17 year old H/AC units: a natural gas furnace that is 80,000 BTU (80% AFUE) and a 2.5 ton AC. The HVAC contractor proposed adding mini-splits to the second floor and updating our furnace and AC for the first floor and basement as follows:
Basement and First Floor:
60,000 BTU furnace and 2.0 ton AC
2-(1 in each bedroom) 9,000 BTU minisplit indoor units (Mitsubishi MSZ-GL09NA-U1)
Outdoor unit (Mitsubishi MXZ-2C20NAHZ)
The minisplits seem oversized to me but they did run Manual J calculations. They were afraid that putting just 1 unit on the second floor wouldn’t keep the other room comfortable as cool air would go down the stairs and hot air would get caught in the hallway. How does the community feel about this solution?
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