Hot Water Cylinder Sizing - Dimensioning

Hot water cylinder sizing is not and should not be complicated, particularly for a domestic installation. There are however a few things that the installer should take into account when selecting a cylinder size


The most important rule of thumb is that a cylinder should be sized to a property, not to who lives there. A single person living in a 5 bedroom,3 bathroom property will not use much hot water, but the property should have at least a 250 litre cylinder to allow for a large family to move in at a later date. The exception to this rule , obviously, is that if a 6 person household lives in a 3 bedroom property, the cylinder should be selected larger than the house would normally require.

Domestic cylinders are typically available in 6 sizes from 120 to 300 litres. If we take the most “standard” installation, a 4 bedroom house with gas central heating and a bathroom and ensuite shower, a 180 litre would typically be suitable. A very rough rule of thumb is when you add a bedroom or a bathroom/ensuite, increase it by one size.

Modern hot water cylinders heat up quickly and cool down very slowly. Mid-sized cylinders will heat up in about half an hour, and take days to lose heat. If you heat a cylinder up on Monday morning and don’t use the hot water, it will still be useably hot on Wednesday or Thursday.




For Commercial sizing advice please contact OSO hotwater

Hot water cylinder sizing