Installing a Ductless Minisplit Head in a Bedroom
My home is a 1950s Cape style house in central Massachusetts. The 2nd floor includes two bedrooms with mostly sloped ceilings. Air sealing and insulation have been done in the ceiling, exterior and knee walls. These two bedrooms each have one tiny supply duct from the central furnace. In the freezing weather, room temps can be 10F colder than the 1st floor. In the summer these rooms get incredibly hot. Window ACs work, but occupy the only window in each room and we need something quieter.
Neighbors with similar houses have added central cooling along with new supply ducts to these rooms. This delivers enough heat, but does not provide adequate cooling. I’ve discussed adding supply + return duct runs plus creating a separate zone for the 2nd floor with HVAC installers. Because the second zone is so small (design cooling load of 6000 BTUs) a modulating furnace and modulating AC/HP with or without a bypass damper were suggested. I didn’t feel confident that this would be ideal for comfort or the equipment. Could this work well?
Most installers suggest (the simple route) of adding a Mitsubishi mini split head to each of these two bedrooms. This is appealing for the high confidence in achieving comfort without losing closet space to new ducts. I would prefer two single-zone systems for better efficiency and comfort. The 6000BTU high wall units would only fit in locations that would be over beds. The floor mounted units (KJ) look to suit the rooms, but are available no smaller than a rated 9000BTUs, with a minimum rated cooling capacity of 2300 BTUs. This is below design load, so I imagine they would work well enough. We also plan to leave the bedroom doors open to encourage cold air to fall down to the first floor.
Ducted mini splits haven’t been proposed, and I don’t see how a ducted system would work. There is a low hallway ceiling and no usable attic space overhead, or behind the knee walls.
Is there another option I am missing, or are single zone ductless mini splits a good option here? Would it be an especially terrible idea to set both heads to the 20,000 BTU multi zone outdoor unit (MXZ-2C20NAHZ2) considering its lowest cooling output is more than double the design cooling load?
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