What size radiators should be used on heat pump installations?

For a heat pump to perform to its highest energy-efficiency, the ‘emitter’ (e.g. radiators or underfloor heating) system should be designed so that the mean water temperature within is as low as possible.

This means that radiator requirements may differ for different heat pump installations.

When radiators are being used either in new properties or existing situations, a flow temperature of 45-50oC is our design figure, but again these will fluctuate due to the weather compensated controls.

Therefore, radiators outputs must be increased to provide the same level of required comfort that would have been obtained from a traditional gas/oil boiler system supplying 80oC flow temperature to the system.

Low flow temperatures have the following benefits:
* Comfort – steady, consistent temperatures provide optimal comfort
* Economy – higher CoP of heat pump and lower system losses
* Health – lower air velocity means less dust disturbance

A well-designed under floor heating system operates very effectively in the temperature range of 30-45oC and as a result is the most effective means of supplying heat to a dwelling.

The sizing of heat emitters (radiators) should be carried out in accordance with the Domestic Heating Design Guide and BS 5449:1990.

Radiator outputs should be checked against any variation in the manufacturers’ catalogue data.