Size the home in plain language
Four answers, a defensible load. The same factor model the full suite uses, with the engineering one click away when the homeowner asks why.
2 x 20x25 filter-back return (or 400-800 sq in net free area equivalent)
Airflow rules of thumb (400 CFM per ton nominal, 350 humid / 450 dry; return free-area sizing). Confirm with a static-pressure test and Manual-D before install.
Plan for this house
Furnace home keeping fossil backup: dual fuel gives heat-pump savings with furnace security on the coldest days. Set the balance point.
Lead with Dual fuel (heat pump + existing furnace): Heat-pump savings for most of the year, furnace security on the coldest nights, nothing removed. Present the 2 brand-neutral fallback option(s) only if the homeowner declines the heat pump, and always price the lit option beside any fallback.
- Supply the electric rate, fuel price, and HP COP to compute the economic switchover. Without them the switchover is set on capacity (thermal) alone.
- Heat pump meets the load to the tested floor. No capacity switchover needed; the furnace is redundancy or pure economic backup. Set the switchover on economics if rates are supplied.
- Run is 0.4 ft past the 24.6 ft factory pre-charge: add refrigerant per the model charge rate (see refrigerantChargeEstimate) and weigh it in.
- Dual fuel requires a dual-fuel-capable control with an outdoor sensor to stage heat-pump-to-furnace on outdoor temperature. Do not run the furnace and heat pump together.
- A C (common) wire is required for modern wifi / smart controls. Verify a true common is landed, not a jumper.
- Maintain condenser clearances: ~12 in sides, 24 in service side, 60 in overhead, 6 in back. Confirm exact values against the model install manual.
- Confirm the condensate path: gravity drain if a downhill route exists, otherwise a condensate pump with a float safety switch.
- Snow region: mount the condenser on a stand/riser above the expected snow line, keep the base-pan drain clear, and protect from roof-shed ice. Wall brackets help in heavy drift.