Tools
Heating load calculator from room sizes.
Heated floor area, in square metres, times a watts-per-square-metre band chosen on this page. The result is in kilowatts. It is a planning figure for a conversation, not a heat-loss survey.
Published 13 October 2026. The four bands are assumptions of this page.
Calculate the load
Load
The load appears here. Nothing you type is uploaded.
Assumptions, units and limits
Enter the floor of each heated room, length by width, in metres. You can enter a whole floor as one room. The page multiplies the total floor area by the band you choose, then divides by 1,000 to show kilowatts. It also shows a band 20% either side, because one figure cannot see the glazing, the outside walls or the draughts.
A 5 metre by 4 metre floor is 20 square metres. On the 60 W/m² band that is 1.20 kW. The 20% spread on this page runs from 0.96 kW to 1.44 kW.
- Up to 12 rooms. Each side of a room is limited to 40 metres.
- Ceiling height, window area and air leakage are not inputs.
- The result is space heating only. It does not estimate hot water.
- An MCS heat-pump installation uses a room-by-room heat loss. This page does not do that calculation. Whether the Boiler Upgrade Scheme is still open is on that grant page, with the date it was checked.
- Work on a gas appliance is for a Gas Safe registered engineer. Who is allowed to work on gas in a home sets out that rule. It does not apply to the Malta directory. A qualification appears on a listing only when the record already has it.
| Band | Figure | What it stands for here |
|---|---|---|
| Solid walls, little insulation | 120 W/m² | Solid brick or stone, single glazing, loft insulation under 100 mm. |
| Older cavity, partial insulation | 90 W/m² | An older cavity wall, some loft insulation, and a mix of glazing. |
| Insulated loft and walls | 60 W/m² | A filled cavity or internal wall insulation, about 270 mm of loft insulation, and double glazing. |
| Recent build or a deep retrofit | 40 W/m² | A home built or refurbished to a recent fabric standard. |
Take the figure to a heating business
Open a plumbing and heating list for London, Manchester, Birmingham, Leeds or Bristol and phone the business yourself. There is no account. This site does not pass the job on, and it does not promise a reply. The kilowatts are not a price, and they are not a boiler badge.
The kilowatt figure printed on a combi is often the hot-water output. This page answers a different question: space heating. A boiler that keeps losing pressure is a separate decision about whether to phone someone.
Questions about this load
Is this an MCS heat-loss calculation?
No. An MCS heat-pump installation uses a room-by-room heat loss. This page multiplies floor area by one of four planning bands.
Does the result size a combi boiler?
It is a space-heating load. Hot-water demand is a separate question, and the figure on a combi badge is often the hot-water output.
Do I need an account?
No. The calculator, the lists and the guides open without a sign-in. There is no profile to create.