The hot water flow rate, expressed as litres per minute (LPM), indicates the speed at which the boiler can heat water supplied to the hot water outlets (taps, showers etc). Hot water flow rates on combi boilers can vary from 9.8LPM to 25LPM. Our tables below show hot water flow rates in the right hand column. Boilers are grouped together according to hot water performance. To calculate your hot water requirements you need to consider how many bathrooms you have and how often they are in use at the same time.
A single bathroom property will only require a small combi with a flow rate of around 10LPM. In properties with two or more bathrooms it is important to opt for a higher hot water flow rate as it will be halved if, for example, two showers are in use at the same time. However a system boiler with hot water cylinder is really much more suitable and will give better flow rates using a smaller boiler.
You will notice that the flow rates can vary quite a lot and boilers that appear quite large can have a comparatively low hot water flow rate. Even the cost of the boiler is no indication as to its hot water performance. For example, the Worcester Greenstar Compact 36CDi has a hot water flow rate of 12.9 LMP and costs £1,358 compared with the Viessmann Vitodens 50 35 with a hot water flow rate of 14.5LMP costing just £906.