Pumps work by pushing the water rather than pulling it, therefore it is best to site it as near as possible to the hot water tank, and as low as possible so it remains full of water. This is called a positive head situation.

Single-impeller pumps can be sited above a shower, which is itself above the level of the hot water tank - for example a loft shower. In this instance the pump will increase the flow of the pre-mixed water from the shower mixer, rather than either the hot or the cold supply. By being located above the hot water tank, the pump is in a negative head situation.

If the entire water supply to the house is at a low pressure then centrifugal pumps are ideal for increasing the flow of all the water in the house, from the shower to the WC cistern. The best feature of these pumps is the built in pressure vessel, which allows the pump to be used in a positive or negative head situation, ie in a basement or a loft conversion.