Heat Pump Sizing for 420 m² (4,521 sq ft) — UK & Temperate Maritime (-5°C Design, UK/IE/NZ)
Thermal heat loss calculation, recommended heat pump capacity (kW, BTU/h & HVAC Tons), SCOP efficiency, and annual electricity consumption.
Recommended Heat Pump34.5 kW117,719 BTU/h (9.81 Tons)
Annual Electricity Usage14,900 kWh/yrDelivers 61,092 kWh Heat (SCOP 4.1)
Savings vs Direct Electric46,192 kWh/yrSpecific Load: 80.8 W/m²
Electrical Circuit (230V)60 A BreakerPeak Compressor Input: 10.45 kW
Thermal & Electrical Specification Table (420 m² / 4,521 sq ft)
| Heated Floor Area | 420 m² (4,521 sq ft) |
| Climate Zone & Design Outdoor Temp | UK & Temperate Maritime (-5°C Design, UK/IE/NZ) |
| Building Insulation Envelope | Older Uninsulated Building (85 W/m² Base) (80.8 W/m² Peak) |
| Peak Space Heating Load | 33.94 kW Thermal |
| Recommended Heat Pump Output (Incl. DHW) | 34.5 kW (117,719 BTU/h · 9.81 Tons) |
| Seasonal Coefficient of Performance (SCOP) | 4.1 (340%–450% Seasonal Efficiency) |
| Annual Heat Demand vs Electricity Consumed | 61,092 kWh Heat → 14,900 kWh Electricity |
Frequently Asked Questions
What kW size heat pump do I need for a 420 m² (4521 sq ft) house?
For a 420 m² (4521 sq ft) building with Older Uninsulated Building (85 W/m² Base) in UK & Temperate Maritime (-5°C Design, UK/IE/NZ), the peak space heating load is 33.94 kW (80.8 W/m²). Including domestic hot water allowance, a 34.5 kW (117,719 BTU/h / 9.81 Ton) heat pump is recommended.
How many kWh of electricity does a 34.5 kW heat pump use per year?
With a Seasonal Coefficient of Performance (SCOP) of 4.1 over 1800 full-load equivalent heating hours, the heat pump consumes approximately 14,900 kWh of electricity per year to deliver 61,092 kWh of heat — saving 46,192 kWh/year compared to direct electric radiators.
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