Heat and Light
It goes without saying that all of us would like to have lower heating and electricity bills; so how do we achieve this? Sometimes it will be easy and sometimes it will be very difficult. It entirely depends on what size and type of property you live in, how practical and easy it is to upgrade the thermal properties of your house and whether you are prepared to change the way you live.
The basics: with regards to energy the average house will have two major utility bills to pay...one for heating and one for electricity. Approximately 61% of all energy used in the home will go on space heating, 23% on hot water, 3% on cooking and 13% on lighting and electrical appliances. These figures will vary depending upon how you live in your house (number of occupants, thermostat settings etc). There are many things that one can do to save money without spending money and these are as true today as they were fifty years ago i.e. turn off lights when not in use, turn the thermostat down, don't leave windows open above radiators.
The main fabric of the house, when and to what standard it was built to, will determine how much energy is required to keep the house warm. A house built to 2008 building regulations will require less heat than a similar sized property built say a hundred years ago. Energy loss is measured by means of u-values which are a measure of the amount of energy (heat measured in Watts) that is transferred through an area (measured in m2) of material when there is a 1°C difference in temperature between inside and out. For example: a solid 220 mm solid brick wall (think Victorian house) will have a u value of 2.1 whereas a newly built house with an insulated cavity wall will have a u value as low as 0.33 i.e. the older house will lose heat over 6 times as quickly as the new house. Roofs: un-insulated roofs might have a u value of 2.6 and roofs insulated to 270mm will have a u value of 0.2 (worth insulating then). Single glazed windows have a value of 5 whereas new double glazed windows can get as low as 1.8.
In older properties it is often possible to upgrade the thermal property of the fabric of the building by adding loft insulation, filling a cavity wall or fitting internal or external insulation and by replacing windows with double glazed windows. The easiest one of these is obviously loft insulation which also has the quickest pay-back.
So to work out how much heat you need you can work out the size of the building and an overall heat loss figure for the fabric which will be in the range of 100 - 300 kWh/p.a./sq meter So a 150 sq m house built to 2008 building regulations might require 100 kWh p.a. per sq meter i.e. 15,000 kWh. An older property which has a heat loss of 300 kWh would need 45,000 kWh to heat the same space. An average house needs approx 23,000 kWh of energy for heating and hot water and approx 3500 kWh of electricity annually.
From all the houses that we have surveyed the amount of energy required annually varies from 9912 kWh (small thermally efficient flat) to 183,159 kWh (large detached older house). Quite a difference.
How much does a kWh of energy cost? At current prices we estimate the cost of different forms of heat as follows:
Oil - 5.35p, Electricity - 14.5p, Gas - 4.03p.
So using the property examples above the flat would cost £399.00 in gas and £530 in oil and the large house would cost £7381 in gas and £9799 in oil. (We have not taken into account boiler efficiencies).
Renewable energy systems can very much reduce the amount of oil or gas needed to heat a home/provide hot water and these are discussed at length on other pages but we hope that this has given you an overview of some of the variables and numbers involved.
