The Domestic Energy Performance Certificate (EPC) explained
To understand the EPC fully you have to have a background knowledge of how the rating is made.
The baseline is for all dwellings has to have a starting point. The SAP rating, as it is know, is a measure of the annual cost of maintaining an acceptable (standard) temperature regime in a dwelling (at a standard location) and supply the dwelling with adequate hot water.
The running costs are calculated using a standard (average) heating pattern. This average heating pattern calculates 9 hours of heating a day (for morning and evening heating) during the week and 16 hours a day at the weekend, with the living area heated to 21 Deg C and the rest of the house to 18 Deg C.
This is the baseline property which works by estimating cooking, lights and appliances, and hot water use for the size of the property, the number of people and the fuel use. Using the measured area and insulation levels from the survey, or from drawings, to work out the heating needed.
The standard rating is calculated on the basis of a 'standard occupancy'.
This is essential because the way occupants use a property can increase or
decrease its energy use. A standard location is also taken into consideration
because the closer to the equator that a property is the less heating will
be required due to the ambient air temperature.
Primarily, the rating of the property depends on the efficiency of the heating system and the ability of the property to maintain that heat through insulation. This is why the heating system, fuel, glazing, wall and loft insulation are so important and has a serious effect on the final score.
