We are seeking to switch from an inefficient oil-fired furnace in our long, cape style home in CZ4 (looks more like a ranch: 2700ft first floor, 900ft 2nd floor). Room-by-room load calculations suggest total heat loss (including basement) of just over 70,000 btu/hr. (R4 stone walls cannot easily be insulated – we have made significant envelop upgrades elsewhere.) The load calcs were performed by a RESNET rater and seem reasonable – do not account for sun orientation but based on volume, glazing, leakage, and insulation. In one area of the home we have an electric baseboard heater and also a propane fireplace.
Our thought is that a single ASHP unit will cost about 10k installed, and we can use another 5k to finish our envelope upgrades. We’d prefer multiple units or minisplits, of course, but the up-front cost would double. We live in an area where nat gas is not available, but many folks have “geothermal” GSHPs.
Thus, our tentative plan is to heat the home (using the existing 1955 high-quality galvanized ductwork) with one 5-ton heat pump (i.e., perhaps Carrier 18vs or Bosch – cooling is less of a concern, because there is an old AC unit in the attic). These ASHPs can generate heat of about 60k of BTU/hr down to 17 degrees, which is our 99% design temp per EnergyStar. Then, after installing the ASHP, if airflow or heat is insufficient, we could add more ducts, mechanical zoning, or a separate zone via a ducted minisplit. We’ve just begun to seek bids.
Does this plan seem reasonable? Is there a rule of thumb for payback on zoning (how much would zones reduce our monthly costs)?
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