5000 - 10000 > CW3: Kitchen tap or shower use:

A CW3 boiler supplies at least 6 liters of water per minute (60 degrees). You can take a hot shower at approximately 10 liters per minute (40 degrees). For comparison, a standard shower head lets through about 9 liters of water per minute; a good water-saving shower head provides approximately 7 liters of water per minute. If you do not want to tap hot water elsewhere at the same time, you will be fine with a CW3 boiler. If you have a bath, rain shower or want to tap hot water at several locations, you will soon need a higher CW class.

10000 - 15000 > CW4: kitchen tap or shower/bath use

A CW4 boiler can fill a 120 liter bath in 11 minutes with a water temperature of 40 degrees. From the kitchen tap you get water at 60 degrees at a minimum of 7.5 liters per minute. If you want some hot water comfort in your home, a CW4 boiler is sufficient in many cases. Would you like to tap hot water at multiple points at the same time? Then it is best to choose a CW5 boiler.

15000 - 18000 > CW5: kitchen and shower tap possible at the same time

A good CW5 boiler is able to tap hot water at two points simultaneously. This type of boiler supplies approximately 15 liters of water per minute (40 degrees). In practice, this means that a CW5 boiler can fill a 150 liter bath with hot water in 10 minutes. Showering in two places at the same time with a water-saving shower head is also easy to do with a CW5 boiler.

18000 or higher > CW6: kitchen and (drain) shower tap possible at the same time

A CW6 boiler is the highest CW class in the market. These boilers work best in large detached houses that require a lot of heating. If this is not the case, the boiler will quickly become less efficient, because the minimum power of CW6 boilers is higher than other boilers.