So, you've assessed the situation and have discovered that your home isn't exactly a shining example of energy efficiency. You know you need to make changes, but where on earth should you start? When it comes to retrofitting, there are generally five key areas that need attention. Here, we look at what action we can take within each of these.

WATER

Domestic water use in the UK is around 150 litres per person per day. But the hot water we use is only part of the problem; the supply of mains water is also energy intensive and has hidden CO2 costs: taking water from the environment, treatment and supply and dealing with sewage. The Environment Agency estimates that 6% of the UK's annual greenhouse gas emissions relate to water use, and nearly 90% of those emissions are from domestic water use. Water efficiency therefore means energy efficiency. Simple measures include lagging pipes and turning off taps when they are not being used, and low-flow showerheads could cut the carbon footprint of hot water by 30%, saving the average home £225 in water and energy bills.

WINDOWS AND DOORS

Windows lose around 18% of your home's heat energy. Double glazing, which should carry the Energy Saving Recommended logo, can halve heat loss by trapping air as an extra layer of insulation. To save on costs you could choose the rooms where your heating demand is high, such as the living room. But if you can afford to have double glazing fitted in all the windows in your home, it would save you around £135 a year on heating bills, which is the equivalent to around 720kg of carbon dioxide a year. Draughtproofing your home can make a dramatic difference to your bills, saving you around £25 a year on heating, and reducing emissions by around 130kg of CO2 each year. Some 12% of heat is lost through ventilation and draughts, and another 3% through badly sealed doors. Adhesive foam strips can be stuck to door frames and around windows, but draughtproofing strips made from brush or rubber which screw into wood are the most effective and durable. Even filling in the gaps on timber flooring or around skirting board with silicone can reduce your bills by £20 a year.

ROOF INSULATION

Around 26% of heat is lost through the roof and as loft insulation is relatively cheap, particularly since the government introduced a 50% discount through energy suppliers, it makes sense to start at the top of your house. The recommended depth for mineral wool insulation is 270mm; however, other materials require different depths. If you'd prefer an environmentally friendlier material than fibreglass, Thermafleece made from sheep's wool, or Warmcel cellulose made from recycled newspaper are effective alternatives. Insulating your loft from scratch with the recommended depth of mineral wool will save around £150 a year, around 800kg in carbon emissions and pay for itself in 2-3 years.

WALL INSULATION

Cavity wall

Walls lose around one third of all heat from detached houses. Insulating cavity walls reduces heat loss and can save you around £115 a year on your fuel bills. If your home was built from 1920 onwards, the chances are that its external walls are made of two layers with a small gap or "cavity" between them. Cavity wall insulation would save around £115 a year, cost £250, pay for itself in two years and save around 610kg.

Solid wall

Wall insulation can be an expensive exercise but could make you dramatic savings of around £400 a year, or around 21 tonnes of CO2. External insulation involves adding a weatherproof insulating treatment to the outside of your wall. Internal insulation involves insulating plasterboard with a thickness of around 90mm. The construction of the laminates reduces the amount of heat which would otherwise pass through into the wall and disappear outside. It will save you around £380 and around 2 tonnes of CO2 annually.

HEATING AND BOILERS

Gas boilers produce 60% of the CO2 from our homes. If your boiler is more than 15 years old then it's likely to be G-rated. Replacing it with an A-rated condensing boiler, with a good thermostat, could cut your heating bills by as much as £235 a year, and save 1,300kg of CO2. Lowering your thermostat by just 1C could save you around £55 a year. In condensing boilers, a heat exchanger converts heat that would otherwise escape up the flue and produces more heat per kW of gas burned. Combination boilers power the central heating and produce hot water on demand. Regular condensing boilers heat water through a cylinder, even when you don't need it. But a kitemarked insulating jacket on a cylinder could save you around £12 a year and cost around the same.

Ground source heat pumps, usually made from pipes buried in the garden to extract heat from the ground, are expensive to install — between £6,000 to £12,000 — depending on the size of your house. But it could save up to 540kg of CO2 and £160 a year if replacing an oil-fired central heating system. Solar thermal systems can be effective even in Britain's temperate climate when used to preheat water for a boiler. Costs range from £3,000 to £5,000 and will save  around £50 a year, and 260kg of CO2. Solar photovoltaic (PV) panels convert sunlight into electricity. Costs range between £8,000 and £14,000 and can knock around £200 off your electricity bill annually, saving  almost one tonne of CO2 a year.

LIGHTING

The first thing you can do is make the most of natural light so that you don't need to switch on the lights. But it's a trade-off. Large windows lose a lot of heat, although triple-glazed windows should solve this problem. So-called "sun pipes", which focus light down a mirrored tube, are becoming increasingly popular, and brighten darker areas such as stairwells even on the darkest days.

Energy-efficient lightbulbs use up to 80% less electricity than standard incandescent bulbs, which are being phased out. A house fitted with compact fluorescent lightbulbs (CFLs) would save up to £37 a year, and £590 over a 10-year lifespan of bulbs fitted throughout the house.