I’m at the point of choosing an HVAC system for my house, and the process is easily the most frustrating experience of the building process thus far. The house is new construction in climate zone 4A, I have taken care to air seal well (OSB seams taped), I will have a closed crawlspace with R10 insulation, R21 dense pack fiberglass in the walls, and R40 loose cellulose on raised heel trusses. I have double pane, low e windows, with minimal exposed glass on the west and east sides; I do have some glass on the south, but I included a brow roof that should shade the south glass through the hottest part of the summer. The house is a true two stories with a relatively open floor plan, and there are minimal penetrations into the attic space. The actual floor space (i.e., not counting the room taken up by the exterior walls) is 1,782 square feet (891 square feet/floor).
My problem deals with sizing the units. I ran load calcs through Manual J software, and the numbers I’m getting just don’t jive with what I’m being quoted. My calculations suggest a bit under 2 tons capacity, but all my installers are recommending 3 to 4 tons. I’ve talked to three different folks now, and they’re all coming in with substantially higher recommendations than my calculations.
I have two related questions:
1) Does my load calc sound reasonable, or am I way off? I’m obviously not an HVAC professional, but I do know how to plug numbers into computer software. I realize you can’t provide me with an actual answer, I’m just hoping to be told whether my numbers sound completely off base given the experience of the community here at GBA.
2) I have been primarily considering minisplits, but I’m wondering if the community may have a better suggestion for my situation. I’m in a part of the world with relatively warm summers (plenty of days in the low-mid 90s with high humidity) and somewhat cool winters (normal temps in the low-mid 20s, with occasional drops below zero). I plan on using a wood stove for the bulk of my heating needs, but I am sometimes gone for up to 2 weeks during the winter (and thus need to provide a stable heat source when no one is at home to feed the fire). I’m installing efficient ceiling fans and casement windows, and plan on using these for cooling as much as possible, though our area’s humidity can sometimes hamper these efforts. Does anyone have any ideas as to a different system (i.e. not a heat pump) that will provide good efficiency under these conditions?
Thanks for any ideas,
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