Rules of thumb

All the estimates given on this page are very rough generic figures and may not apply in specific circumstances. They should not be used as the basis of investment decisions.

Space heating

Dropping  average space temperature by 1°C  will save about 8% on heating fuel requirement


A 1% fuel saving will result from a 20°C reduction in flue temperature or a 15 percentage-point reduction in excess air

Air compressors

Reducing inlet air temperature by 6°C will improve efficiency by 1%

Reducing discharge pressure by 1 bar will save 6% energy

Tip: turn off the air supply out of working hours and time how long it takes the pressure to drop by 1 bar. Dividing the volume of your air receivers by the measured time gives a direct estimate of the air loss rate.


A 3% improvement in chiller compressor efficiency will result from a 1°C reduction in condenser temperature or 1°C increase in evaporator temperature.

Steam leaks

Tip: observe the plume from an electric kettle of known power (e.g. 2kW). When you see a steam leak, compare the size of its plume to estimate the corresponding energy loss.