SAP Rating Estimator — Simplified Energy Performance
Estimate SAP rating from fabric heat loss, heating system efficiency, and renewables. Gives approximate EPC band for UK dwellings.
Gross internal area
0.30 typical existing, 0.16 Part L
0.16 Part L limiting, 0.11–0.13 notional
0.18 Part L limiting (new-build), 0.13 notional
1.4 double, 0.8 triple
Part L target: 8
Reduces net energy consumption
How We Calculate This
This estimator approximates a SAP rating by calculating fabric and ventilation heat losses, applying heating system efficiency, and accounting for any renewable energy contribution.
The formula
Fabric loss (W/K) = Σ(Element area × U-value) + Thermal bridging
Ventilation loss (W/K) = 0.33 × Ventilation rate × Volume
Annual energy = Total loss × Degree hours ÷ 1000
Delivered energy = Annual energy ÷ Heating efficiency
ECF = (Annual fuel cost × 0.85 deflator) ÷ (TFA + 45)
SAP = 117 − 121 × log₁₀(ECF) (when ECF ≥ 3.5, else 100 − 13.95 × ECF)
Based on BRE SAP 10.2 methodology with notional fuel tariffs (gas 3.87p, electricity 15.41p, oil 4.64p per kWh). Includes space heating, DHW, pumps/fans, lighting; solar PV deducted.
Frequently Asked Questions
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Last updated: March 2026
All calculations are estimates. Verify with your supplier.