Size the house at the real outdoor temperature
Four answers. A heating and cooling load using the ASHRAE outdoor temperature for that state. Show the math when they ask how you got it.
Hydronic home with no ducts: forced-air conversion needs new ducts; ductless multi-zone is usually faster and cheaper. Compare both.
Coverage band: undersized. Deal basis: estimated.
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
Hydronic home with no ducts: forced-air conversion needs new ducts; ductless multi-zone is usually faster and cheaper. Compare both.
Lead with Boiler / hydronic to heat pump: Move off the boiler to a heat pump that heats AND cools, something the boiler never did. 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.
- Hydronic boiler home: an air-to-air heat pump cannot share a control with the boiler the way a furnace coil does. Keep the boiler as an independent backup, or convert to forced-air. This is not an integrated furnace dual-fuel job.
- A new air-zoned heat pump is overlaying an existing hydronic-zoned boiler. These are two independent zoning systems: the air dampers/heads and the boiler zone valves must not share a controller. Plan separate controls.
- 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.
- Confirm the O/B reversing-valve orientation against the equipment (most energize O on cool).
- 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.