SAP 10.3, HEM & the New Calculation Methodology
The government has confirmed a phased transition from SAP to the Home Energy Model. Here's what this means for compliance, assessors, and the industry.
SAP 10.3 vs Home Energy Model
| Feature | SAP 10.3 | Home Energy Model (HEM) |
|---|---|---|
| Available from | FHS launch (March 2027) | At least 3 months after March 2026 |
| Heat pump sizing | Fixed COP of 2.5 for all dwellings | Dynamically sized to individual dwelling |
| Thermal mass | Simplified assumptions | Full thermal mass modelling |
| Occupancy patterns | Standardised patterns | Realistic occupancy patterns |
| Delivered energy reporting | Not available | Voluntary reporting via BREL |
| Minimum availability | 24 months from SI being laid | Ongoing — intended to become sole methodology |
| Status | Interim approved methodology | Government's preferred long-term methodology |
Phase 1: SAP 10.3 at Launch
The FHS launches with SAP 10.3 as the only approved calculation methodology. This updated version of SAP has been produced for both SAP and HEM formats. The SAP notional building uses a fixed COP of 2.5 for all dwellings, as SAP cannot dynamically size heat pumps.
Phase 2: Dual Running
HEM will become an approved calculation methodology no earlier than 3 months after the March 2026 consultation response. Once approved, either HEM or SAP 10.3 can be used for FHS compliance. The dual running period will last at least 24 months from when the SI is laid, giving the sector certainty about the minimum period SAP 10.3 will remain available.
Phase 3: Transition to HEM Only
The government intends to give industry 6 months' notice before setting a date beyond which SAP 10.3 can no longer be used for new building control plans. Transitional arrangements will be structured similarly to standard Building Regulation updates — SAP 10.3 will be authorised for plans filed before a certain date, meaning EPCs produced with SAP 10.3 may continue well beyond the formal closure date.