Stelrad has updated all versions of its heat loss calculator and radiator sizing software, the Chartered Institute of Plumbing and Heating Engineering (CIPHE) reported on 21 January 2026. The package is used by installers and specifiers across the UK heating sector, and the revised versions are available from the Stelrad professional website1.
The changes cover both the Basic Heat Loss Calculator and the Advanced version. Both now incorporate the latest recommended room temperatures and air changes from NHBC Standards 2024 Chapter 8.3, together with associated terms and conditions that include the latest CIBSE u-values1. A new step asks the user to choose between electric and conventional heating, with a revised calculation algorithm to accommodate the choice, and the software displays products according to whether hot water or electrical heating is selected1. Stelrad has also restyled the interface and improved compatibility with modern browsers1.
Sarah Baker, Marketing Communications Manager at Stelrad, said the update responds to the growth in low temperature renewable heating systems:
"With the increasing number of low temperature renewable heating systems out there, sizing radiators and calculating heat loss calculations has never been more important. For this reason, we have decided to upgrade our heat loss calculators, all versions, so that installers, specifiers and homeowners alike can get to grips with this important part of the specification of heating systems."
Baker added that lower temperature heating systems need larger radiators even where insulation levels are better, and that the guides for selecting radiators room by room need to stay current so that sizing calculations come out right1. Stelrad is an Industrial Associate of CIPHE1.
| Item | Detail |
|---|---|
| Basic Heat Loss Calculator | Updated with NHBC Standards 2024 Ch.8.3 room temperatures and air changes; latest CIBSE u-values1 |
| Advanced Heat Loss Calculator | Same updates as Basic1 |
| New step | Choice between electric and conventional heating, with revised calculation algorithm1 |
| Product display | Products shown according to hot water or electrical heating selection1 |
| Interface | Restyled; improved compatibility with modern browsers1 |
Why it matters for households
Radiator sizing determines whether a home reaches its target temperatures on the coldest days. A heat pump or other low temperature system runs at lower flow temperatures than a gas boiler, so the same room generally needs a larger emitter to deliver the same heat output. If the heat loss calculation is wrong, the result is usually a home that never quite warms up, or one where the system runs harder and longer than it should.
The update matters because the inputs behind the calculation have moved. Room temperatures and air change rates from NHBC Standards 2024 and CIBSE u-values feed directly into the numbers an installer or specifier works from, and a calculator using superseded figures can understate or overstate what a room needs. The new electric or conventional heating step also reflects that not every home is on the same fuel, which affects both the radiators and heat emitters chosen and how the system is expected to perform.
For a household, correct sizing is part of what makes a heating system predictable: a home that holds its temperature on its own schedule, on the fuel it has chosen, with less reliance on top-up heating. The software is a tool for the trade rather than a household product, and CIPHE does not report any change to how homeowners access advice or quotes.
What happens next
The updated versions are available now from the Stelrad professional website1. No further release dates, training sessions or revisions have been reported.
Sources1 cited
- Heat Loss Calculator and Radiator Sizing Software, ciphe.org.uk