About this calculator

Rule of thumb: 50 W per m³ for older insulation, 35 W/m³ for modern, 20 W/m³ for passive houses. Multiply by 1.1 for hot-water priority.

Frequently asked questions

What does the Heat Loss / Boiler Size Calculator do?

Quick whole-house heat loss for boiler or heat pump sizing. Rule of thumb: 50 W per m³ for older insulation, 35 W/m³ for modern, 20 W/m³ for passive houses. Multiply by 1.1 for hot-water priority.

Is the Heat Loss / Boiler Size Calculator free to use?

Yes. Every calculator on Calcurly.com is free, works in your browser without sign-up, and can be embedded on your own website.

How accurate is the Heat Loss / Boiler Size Calculator?

Results are calculated in real time using industry-standard formulas. Treat the output as a well-informed estimate — always cross-check with local regulations, product datasheets, or a qualified hvac & climate professional before committing to a purchase or a job.

What inputs does the Heat Loss / Boiler Size Calculator need?

Enter values for: Heated volume (m³), Building standard. Sensible defaults are pre-filled where possible so you can start with a single change.

Can I embed the Heat Loss / Boiler Size Calculator on my own website?

Yes — copy the iframe snippet at the bottom of this page, or use the Embed Generator to customise the size. The embedded version stays in sync with the live calculator on Calcurly.com.