House Energy Audit Calculator
Welcome to the House Energy Audit Calculator (HEAC). The purpose of this calculator is to enable you to see where energy is being lost due to heat escaping from your house. The calculator requires information which you probably know off the top of your head such as the number of rooms, whether you would describe them as small, medium or large, single or double glazing etc. If you do not know, you may need to check how thick the insulation is in your attic, and ask a builder if you have solid or cavity walls. The calculator will then tell you how much each area of your house is costing per year due to heat loss. For example it will say walls £500, windows £200, roof £85 etc. It will also tell you how much each area would cost if you installed effective insulation, so you can see exactly how much energy and cost you would save.
What is the purpose behind the HEAC? It is now widely recognised that CO2 emissions are causing climate change, which threatens nature and civilisation. The UK Government is committed to a 20% reduction of national CO2 emissions by 2012. Domestic energy consumption causes 25% of national emissions, and heating uses 90% of energy in the home. If we could all reduce our household heat-loss by half, that would cut national emissions by 10% and save us a lot of money, without even changing our lifestyles! As you will see from the calculator, it is not that difficult to cut the heat loss from the average house by half, as most old houses leak a lot of heat! New houses are being built to much more stringent energy-saving requirements, so they are not such a problem. But most houses in the Nation are not new, and need to be improved. This calculator helps you see what changes can be made to your house to reduce its heat loss.
Reducing your heat loss will also save you money. The cost of energy is rising steadily because it is more expensive to extract oil from the remaining smaller oil fields. Using less energy will mean that less new energy sources such as windmills or nuclear power stations will be required, keeping the country a nicer, safer place.
We hope you enjoy using the calculator, and find it useful. Good luck!
To use the calculator, enter details about your house, making a selection from the pull down menus or entering a number in the boxes. Example values are in place for a typical three bedroom semi-detached house.
Summary
So, by applying good insulation to your house you can cut heat loss and therefore your energy use and hence your fuel bills by
%
which is a saving of
£ per year
Notes on Accuracy
When you have entered your details into the calculator, it predicts what your annual energy bills should be. You can compare this with your actual annual fuel bills. For an old house your fuel bill will be about 10% more than this prediction, and for new houses 20% more. This extra amount is for your other electrical appliances, which are a greater proportion in new houses, since heat loss is less.
Even if the prediction is different from your actual fuel bills, it still gives you a good indication of the proportion of heat loss in each area of the house. If you would like to understand this inaccuracy, the following points apply:
- Use of general figures: This calculator is based on general figures for house size, temperature, window area, materials and wall thickness. Your house may or may not fit these well.
- Varying room temperature: Unless you have constant central heating in all rooms, room temperature will vary considerably at different times of the day, and between rooms. For example many people only heat bedrooms for a couple of hours before they go to bed. The rest of the day they are allowed to get quite cool. Predicting the average temperature of all the rooms over the whole day is difficult. Again the calculator uses general figures.
- Draughts: Predicting draughts is a very inaccurate business, unless you have a house pressure test done. Even then, the draughts depend on how hard the wind is blowing, how exposed the site is, and how many times the doors and windows are opened in the day.
- Temperature distribution: If you took the temperature in lots of different places in a room it would vary a lot from floor to ceiling, interior to exterior walls and how close you were to doors and windows. If radiators are placed under windows the room is more evenly heated, but more heat goes out the windows. If a radiator is on an interior wall, the area near the window will be colder, but this in turn means that less heat is lost.
- Putting up with it: If you have a poorly insulated house, the chances are that you will put up with a cold house, and heat rooms only when in use. Therefore your average room temperature will not be 15 degrees C, and your fuel bills will not be as high as predicted. If you install good insulation, you may well keep rooms at a warmer temperature rather than save money on fuel bills. However, that is your choice, and certainly in the depths of winter you will save energy, and be warmer!
- Fuel Type: The cost of heating depends partly on what fuel you use. For example gas costs around 4 pence per kilowatt-hour, and electricity about 9 pence per kilowatt-hour. The calculator uses a figure of pence per kilowatt-hour as a guideline. (One kilowatt-hour, or one unit, is a term used for electricity, but can be applied to any type of fuel. A kilowatt-hour is a unit of energy, just like a Calorie. In fact, 1 KWh = 860 Calories).
Mukti Kumar Mitchell, North Devon, June 2005
Sources include:
- James Carvill, Mechanical Engineer's Data Handbook, Butterworth Heinemann, 1993
- DIY Data
- Irish Energy
- Gale & Snowdon Architects