Heat loss calculations: the basics behind correct sizing
A heat loss calculation works out how much heat a room or whole property loses to the outside under design conditions, and that figure underpins correct boiler and radiator sizing rather than relying on rules of thumb. Getting it right avoids both undersized comfort problems and oversized inefficiency.
Heat loss calculations: the short technical version
The calculation factors in wall, floor, roof and window construction and their insulation values, room dimensions and ceiling height, orientation and exposure, and an assumed external design temperature for the local area. Each room is calculated individually because construction, glazing and exposure vary across a property, and the totals inform both radiator sizing and overall boiler output requirements.
Practical notes on heat loss calculations
- Wall, floor, roof and window insulation values all feed into the calculation
- Room dimensions and ceiling height directly affect the result per room
- Orientation and exposure to wind and weather are factored in
- An external design temperature specific to the local area is used
- Each room is calculated individually rather than averaged across the property
Published business details
- Based at 24 Bristol Road, Radstock, BA3 3EE
- Telephone enquiries: 07516 118198
- Opening hours: Monday to Friday, 8:30am to 5:00pm
Questions we get asked
- Is a heat loss calculation always necessary?
- It's the proper basis for accurate sizing, and is standard practice for both new installations and significant upgrades.
- Can I estimate heat loss myself?
- Rules of thumb exist but a proper room-by-room calculation gives a far more accurate and reliable result.
Where we deal with this
Related help pages
- Oil running costsCutting oil heating running costs without cutting comfort
- Cost driversWhen scaffolding or extra access equipment is needed
- ProcessWhat happens when you call about an urgent heating fault
- Running costsOil vs gas running costs compared for 2026
- Baxi fault codeBaxi E133: gas supply or ignition failure on a Baxi combi
- Worcester fault codeWorcester A7: sealed system pressure fault on a Greenstar
Services that cover this
Get heat loss calculations looked at properly
Put simply: Heat loss calculations, done room by room, are the foundation for correct boiler and radiator sizing — not a rule-of-thumb estimate.
Published opening hours are Monday to Friday, 8:30am to 5:00pm.
New Worcester boiler with a 10 year guarantee*
Free no-obligation quotes for installation, servicing & repairs across BA & BS postcodes.