Energy saving house - saving assumptions

It is not always possible to provide accurate savings for each measure. This is due to a variety of factors.

Certain actions cannot be selected together. For example, you cannot install both solid wall insulation and cavity wall insulation, as your walls will either be of cavity or solid construction.

In other cases, the saving for certain actions will change when you carry out other actions. For example if you were to insulate your loft then you would reduce the amount of energy needed to heat your home, so your boiler would not have to work as hard. Therefore replacing your boiler after you have insulated your loft would not save you quite as much money and CO₂ as it would do if you replaced your boiler before insulating your loft. Doing both will save you more money and CO₂ than either action on its own, but the combined savings are more complicated to work out. To keep the interactive house straight forward we have excluded some actions which would make calculating your total more complicated.

The saving for installing a ground source heat pump cannot be added to the savings for insulation measures, because the assumptions used to calculate energy efficiency measures are very different to those used for renewables. Therefore the savings for installing a ground source heat pump cannot be added to the total.

Savings assumptions

Boiler savings
Boiler savings assume replacing a stock average boiler of 72% efficiency with an Energy Saving Recommended condensing boiler of 90% efficiency, average levels of insulation and limited heating controls.

Heating control savings
The saving for installing new heating controls alone assumes moving from only a room thermostat, to a hot water tank thermostat and thermostatic radiator valves with a stock average boiler.

Wash at 30°C
Washing at 30 degrees assumes all washes are done at 30 degrees rather than higher temperatures.

Renewables savings
The saving for ground source heat pump assumes replacing an electric heating system in a fully insulated detached house, with the pump providing 100% of space heating and up to 50% of hot water. Savings will vary depending on the fuel replaced, but are not as favourable for gas heated homes as for other fuels.

The saving for solar hot water is based on the hot water requirements of a three bed semi-detached house with gas hot water heating.

The saving for PV (photovoltaic) panels assumes a 2.5kWp system with 50% on-site consumption and excess exported to the grid on a typical export tariff.

Car savings
The saving for smarter driving is based on an average sized car, is an average of the savings for petrol and diesel cars, and assumes an annual mileage of 8,770miles and a fuel price of 118p/litre for petrol and 131p/litre for diesel.

The saving for walking to school assumes replacing a one mile drive to school and back at the start or end of the school day in an average car with a one mile walk for every day of the school year (190 days).

The saving for buying the cleanest car in class is based on sales weighted fuel efficiency (litres per 100km) for all new cars sold in 2007 and the fuel efficiency in 20007 of the most fuel efficient car in the same class, and assumes an annual mileage of 8,770miles and a fuel price of 118p/litre for petrol and 131p/litre for diesel.

For all other savings assumptions click here