Tools · Plumbing & heating
What size boiler do I need? A rough kW check
Type room sizes for a first look at heating load in older UK houses. This is not a heat-loss survey and not MCS sizing. Gas work still needs Gas Safe.
Watts per cubic metre used here
Each room is length × width × height, then multiplied by the band in the table. Poor is closer to uninsulated older stock. Good is closer to a later insulated house. The table is a rule of thumb, not CIBSE Guide A and not a radiator schedule.
| Room | Poor | Average | Good |
|---|---|---|---|
| Living room | 60 W/m³ | 50 W/m³ | 40 W/m³ |
| Bedroom | 50 W/m³ | 40 W/m³ | 30 W/m³ |
| Bathroom | 70 W/m³ | 55 W/m³ | 45 W/m³ |
| Kitchen | 55 W/m³ | 45 W/m³ | 35 W/m³ |
| Hall or landing | 45 W/m³ | 35 W/m³ | 28 W/m³ |
| Other | 50 W/m³ | 40 W/m³ | 32 W/m³ |
The result shows a ±15% band around that total.
Questions about this kW figure
Is this a heat-loss survey?
No. It multiplies room volume by a watts-per-cubic-metre band. It does not read U-values, windows or air tightness.
Can I use this figure for a heat-pump grant?
No. The Boiler Upgrade Scheme needs an MCS-certified installer. None of the listings here show MCS. This kW band is not that design. Read the grant notes and, if you have a bill, the heat-pump savings calculator.
Who should I call for gas or a boiler?
Open a plumbing list and look for Gas Safe on the profile. Ten businesses here show that mark. The directory does not certify the work.