Heat loss calculations estimate how much heat a property needs to maintain comfortable indoor temperatures in winter conditions. They are central to system sizing for both retrofit and new-build projects.
What data is used
- Room dimensions and layout
- Wall, roof, floor and glazing construction
- Ventilation and infiltration assumptions
- Design temperatures and property exposure
Why room-by-room matters
Whole-house shortcuts can hide weak rooms. Room-level outputs improve emitter sizing and reduce cold spots, noise from overworked systems, and performance complaints.
Common misconceptions
- "EPC is enough": EPCs are useful context, but not a substitute for a full design heat loss calculation.
- "All similar homes are the same": extensions, insulation history and glazing mix change results significantly.
- "One number is all you need": practical design and commissioning decisions often depend on room-level detail.
What good outputs look like
- Clear room-by-room table
- Transparent assumptions
- Evidence supporting key construction inputs
- Layout that is easy for design and install teams to use
Related reading: heat loss surveys, heat loss calculator guide, deliverables.