Power input is the energy used - Often measured in Watts or Kilowatts (kW) and sometimes British Thermal Units (BTU).
1 kW = 3412 BTUs
Heating appliances Gas, Oil or Electric are more usually rated in kW.
The difference between power input and power output is used to determine the overally efficiency.
Modern heating boilers have an efficiency rating in excess of 90% - older ones as low as 65%.
A comprehensive list of UK boilers with their power rqatings may be found here...
http://www.homeheatingguide.co.uk/efficiency-tables.php
Electric fires; in fact all electrical appliances, should have a Rating Plate (sometimes just a sticky label) fixed to them - often at the back - showing the Power Consumption.
Peccavi, October 2009
