Which CW class do I need? CW3, CW4, CW5 or CW6 per household, shower and bath, with the boilers per class

Short answer: the CW class (Comfort Warm Water) does not say how hot the water gets, but how many litres of 60 °C water the boiler can deliver continuously per minute. CW3 (7.5 litres per minute) suits one to two people with one shower; CW4 (just over 7.5 litres, with a 10-minute shower and a 100-litre bath) two to three people; CW5 (12.5 litres, 120-litre bath, two outlets) a family with a bath or rain shower; CW6 (15 litres, 150-litre bath in 10 minutes) two bathrooms or a large rain shower. One class higher costs € 50 to € 100 more to buy and nothing extra in gas: the boiler only uses the output when you run hot water. If in doubt, choose the higher class; you will notice a class that is too low every morning.

The CW classes

Class	Hot water (Gaskeur)	Household	Bathroom	Examples in the shop
CW3	7.5 l/min at 60 °C; shower 6 l/min	1 to 2 people, flat	One standard shower, no bath	Intergas Kombi Kompakt HR 22 (on request)
CW4	7.5 l/min; 10-minute shower; 100-litre bath in 12 minutes	2 to 3 people, terraced house	One bathroom, standard shower, small bath	Remeha Avanta Ace 28c € 900, Intergas HRE 28/24 € 999, Nefit ProLine NxT HRC 24 €1,090, Intergas Xtreme 30 €1,365
CW5	12.5 l/min; shower of 12.5 l/min; 120-litre bath in 10 minutes; two outlets at the same time	4 or more people	Bath or rain shower, or shower and kitchen at the same time	Remeha Avanta Ace 35c € 999, Intergas HRE 36/30 € 1.099, Nefit ProLine NxT HRC 30 €1,190, Intergas Xtreme 36 €1,465
CW5+ / CW6	15 l/min; 150-litre bath in 10 minutes	Large families	Two bathrooms, large rain shower, jacuzzi	Remeha Calenta Ace-Matic 40c € 1,479 (CW5+); Intergas Prestige CW6 on request

The class is shown on the rating plate of your current boiler as a Gaskeur CW label (how to find it). For boilers from before 2005 you can derive it from the hot water output: 24 kW corresponds to CW4, 28 to 30 kW to CW5, 35 kW and above to CW6.

Calculate with your shower head

The class system assumes a shower of 6 to 8 litres per minute. Modern shower heads achieve that; a 30 cm rain shower uses 12 to 20 litres per minute, and that changes everything. A CW4 delivers 7.5 litres at 60 °C; mixed with cold water to 40 °C, that is about 11 litres of shower water per minute. With a 15-litre rain shower the boiler cannot keep up and the shower turns lukewarm as soon as someone else opens a tap. Check the packaging or the specification of your shower head: up to 9 l/min CW4, 9 to 13 l/min CW5, above that CW6. A water-saving rain shower (9 l/min) makes CW4 feasible again.

Peak moment	Minimum class
One person showering, standard head	CW3
Shower and kitchen tap at the same time, or bath up to 100 litres	CW4
Rain shower 12 to 15 l/min, or 120-litre bath	CW5
Two showers at the same time, or rain shower plus kitchen	CW5 minimum, CW6 comfortable
Two bathrooms in use, bath of 150 litres or more	CW6

CW class and output are two different things

The CW class is about hot water; the central heating output (kW) is about heating. An Intergas HRE 36/30 has 30 kW for hot water (CW5) but modulates down to a few kW for heating; an HRE 36/48 has the same hot water output but 48 kW for central heating, for large homes. Choose the heating output based on the heat loss of your home (how to calculate it) and the CW class based on your hot water needs. For an average home, 5 to 10 kW of heating output is enough; the high number in the product name is almost always the hot water output.

Is higher always better?

The class makes little difference to gas consumption: the boiler only uses the higher output while running hot water, and a larger unit modulates down just as low for heating as a smaller one. In price, one class makes a difference of € 50 to € 100 for the boiler alone and roughly the same installed (all prices). The downsides of going too high: a CW6 in a flat with one shower is unnecessarily large and heavy, and with some brands a larger unit has a higher minimum modulation, so it cycles on and off more often in a small, well-insulated home. So do not go two classes higher than needed, but do go one higher if you are in doubt or if a rain shower or second bathroom is planned.

Alternative: add a cylinder or heat pump

If you want to combine a lower class with plenty of comfort, a storage cylinder next to the boiler (indirectly heated, 80 to 150 litres) can absorb the peak; see Buying a hot water cylinder 2026. With an all-electric heat pump the CW class no longer applies at all: the hot water then comes from a cylinder of 150 to 300 litres and its size determines the comfort, see Hybrid or all-electric.

All boilers by class are in the · ; the complete selection guide is in Which boiler suits my home?. Not sure? Send a photo of your current rating plate and tell us how many people there are and what kind of shower you have; we will advise on the class.

Frequently asked questions

What exactly does CW mean?

Comfort Warm Water, a Gaskeur label (a Dutch quality mark) that indicates how much hot tap water the boiler delivers per minute and how quickly a bath fills. The classes run from CW1 to CW6; in practice, combi boilers are sold from CW3 to CW6.

My current boiler is CW4 and the shower turns lukewarm when the dishwasher starts. What now?

A dishwasher uses cold water and heats it itself, so it is usually not the cause; a kitchen tap or second shower is. When replacing, go one class up to CW5.

Does a CW5 use more gas than a CW4?

Not for heating; it only delivers more output while running hot water, and that is water you would heat anyway. The difference in annual consumption is negligible.

Which class do I need for a 180-litre bath?

CW6, or CW5 if you are happy with 15 minutes of filling. For a bath that is used often, a storage cylinder next to the boiler is also worth considering.