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Home and heat-pump inputs
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Quick mode estimates the building heat loss from floor area, temperature difference, ceiling height and insulation profile. Heating distribution is shown as equipment-selection guidance and does not change the building heat loss.
Building geometry and design conditions
Envelope and ventilation
The detailed model estimates wall, window, roof, floor and ventilation heat loss. It remains a whole-building approximation and does not replace room-by-room design.
Proposed heat pump and annual use
Heat-pump result
Capacity comparison
| Heat-loss component | Design loss | Share |
|---|
What the results mean
- Design heat loss is the estimated heat required at the selected winter outdoor temperature.
- Cold-weather coverage compares building demand with the unit's entered output at that temperature.
- Backup heat is the remaining peak capacity gap. It does not predict annual backup-energy use.
- Annual electricity uses the entered annual useful heat divided by SCOP. Backup-heater energy is not estimated because it depends on the local temperature distribution and controls.
Heat-pump selection checks
- Check the manufacturer's capacity table at the actual outdoor temperature and required supply-water or discharge-air temperature.
- Check minimum modulation, not only maximum output.
- Confirm electrical service capacity, backup-heater power, noise, defrost drainage and emitter compatibility.
- For hydronic systems, lower supply temperatures generally support better efficiency.
Calculation basis
Transmission: Q = U × A × ΔT
Air loss: Q ≈ 0.33 × Volume × ΔT × [infiltration ACH + ventilation ACH × (1 − heat recovery)]
Annual electricity ≈ annual useful heat ÷ SCOP
Quick mode uses a calibrated heat-loss intensity and is suitable only for early screening. Heating-emitter type is not used to alter the building heat loss. Detailed mode is more transparent but still simplified: thermal bridges, solar gains, internal gains, ground-temperature variation and intermittent heating are not fully modelled.
Further checking: compare the result with a recognized load calculation and manufacturer performance data at the selected outdoor temperature. See ENERGY STAR air-source heat-pump guidance and the Building Science Education cold-climate sizing material.
Common sizing mistakes
- Using only floor area or the old boiler rating.
- Using nominal heat-pump capacity measured at mild weather.
- Ignoring radiator or supply-water temperature.
- Assuming SCOP is the same as COP at the coldest hour.
- Adding a large arbitrary oversizing margin without checking minimum output.
Frequently asked questions
There is no reliable universal value. Outdoor design temperature, insulation, airtightness, glazing, ventilation and indoor temperature all affect the result. Floor-area estimates are suitable only for early screening.
Use the design heat loss and compare it with certified heat-pump output at the local design outdoor temperature. A professional calculation should confirm final selection.
COP is performance at one condition. SCOP or seasonal performance factor represents average seasonal performance and is more appropriate for annual-use estimates.
The home's load rises in colder weather while some heat pumps lose capacity. Backup heat covers the difference.
No. Excessive oversizing can cause cycling and poor mild-weather operation. Capacity range and controls matter.
No. It is intended for comparison and early planning.