Short answer: a commonly used rule of thumb is 60 tot 100 watt per vierkante meter of floor area at a normal ceiling height (2.5 m). Well-insulated house: about 60 W/m². Averagely insulated: about 80 W/m². Old and poorly insulated: 100 W/m² or more. A 25 m² living room in an average house therefore needs about 2,000 watts. This is an estimate; for a heat pump or a room with a lot of glazing, a heat loss calculation is better.
Worked examples
| Room | Area | Well insulated (60 W/m²) | Average (80 W/m²) | Poorly insulated (100 W/m²) |
|---|---|---|---|---|
| Bedroom | 12 m² | 720 W | 960 W | 1.200 W |
| Kitchen | 15 m² | 900 W | 1.200 W | 1.500 W |
| Living room | 25 m² | 1.500 W | 2.000 W | 2.500 W |
| Large living room | 35 m² | 2.100 W | 2.800 W | 3.500 W |
If the ceiling is higher than 2.5 metres, allow proportionally more. A room with a lot of glazing, external walls on two sides or above a crawl space also needs more.
From watts to radiator
The output of a radiator depends on type, height and length, and on the water temperature. Manufacturers usually state the output at 75/65/20 °C (flow, return, room). As a guide, a type 22 of 600 × 1000 mm gives about 1,600 to 1,750 watts at that temperature, depending on the brand. Not enough output in one radiator? Choose a longer radiator, a higher type, or spread it over two radiators.
With a heat pump
At a flow temperature of 45 to 50 °C, a radiator gives about half of its output at 75 °C. So allow for about twice as much radiator surface, or have a heat loss calculation done. See also does a heat pump work with ordinary radiators?
Know the output you need? Take a look at the Radson Compact radiators or send us the dimensions of the room via WhatsApp and we will help you work it out.
Frequently asked questions
Hoeveel watt radiator heb ik nodig per m²?
As a rule of thumb, 60 watts per m² in a well-insulated house, 80 watts in an average house and 100 watts or more in an old, poorly insulated house, at a ceiling height of 2.5 metres.
How many watts for a 30 m² living room?
In an averagely insulated house, about 2,400 watts (30 x 80). That can be one large type 22 or type 33 radiator, or two smaller ones.
Is an oversized radiator a problem?
No, a slightly oversized radiator is not a problem: the thermostatic radiator valve regulates the heat. A radiator that is too small will not heat the room enough on cold days.