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From The Sunday Times

January 20, 2008

Going green: how much does it cost and is it worthwhile?

Can’t build a new home from scratch? Don’t despair: there are plenty of ways to make your existing house green. And, although payback times are long, government grants will cover part of the costs

Sian Griffiths

Wind turbine

Installed on the roof or, for bigger turbines, on a mast in the garden. Great on windy coastlines or mountains, but not in towns or cities. May need planning permission.

Cost? Depends on size: from £2,000 up to £20,000 for a system that covers a household’s entire electricity demand.

Payback time? Eight years or more.

Solar photovoltaic electricity

Solar panels generate electricity as the sun's rays hit a silicon layer.

Cost? Varies with size: perhaps £10,000 for a household system. If you generate surplus electricity, you can sell it back to the grid.

Payback time? More than 20 years.

Solar water-heaters

Collects warmth from the sun, heating water, which is then pumped through a coil in the hot-water tank. Best on south-facing roofs. It requires a hot-water storage tank and, in the UK, there is only enough sun to let you switch off the boiler six months a year.

Cost? Typically £2,000 to £4,000.

Payback time? More than 20 years at current gas prices.

Better central heating controls

Inefficient controls mean many households waste energy. Look at intelligent alternatives such as the Dataterm, a combined thermostat and central heating programmer.

Cost? About £500 for a completely new installation.

Payback time? About seven years.

Condensing boiler

Up to 30% more efficient than traditional boilers at converting fuel into heat.

Cost? About £1,500.

Payback time? Eight to 10 years.

Insulating your loft

Increase it to a thickness of 25cm. The greenest insulating material is sheep's wool, but you can buy standard material from DIY stores. Foam backed with aluminium foil is the high-tech option.

Cost? A few hundred pounds.

Payback time? Two or three years.

Insulating walls

Cavity-wall insulation is a cheap and reliable way of keeping more heat indoors. It won’t work in older houses: consider cladding the outside with insulating material and rendering over it.

Cost? About £500.

Payback time? Two or three years for detached houses.

Woodburning stove

Consider a stove that heats water for central heating. But you may not be allowed to burn wood in clean-air zones in city centres.

Cost: £2,000 to £5,000.

Payback time? Five to 10 years.

Double glazing

Replacing draughty wooden windows is a pricey way of making your home greener.

Cost? About £500 per window.

Payback time? More than 10 years.

Tip: get estimates from local specialists as well as the big firms. They are often cheaper.

Ground-source heat pump

Extracts warmth from the soil for underfloor heating. Makes more financial sense if your house is not on a gas main: it runs on electricity, which is about four times as expensive as gas per kilowatt hour. You need a big garden.

Cost? £6,000 to £12,000 for installation.

Payback time? Probably more than 15 years.

Insulating your door

Consider replacing a wood and glass door with a thick plastic one made to look like wood.

Cost: £250 to £500.

Payback time? More than 10 years.

I know that I replaced my 20yr old perfectly functioning boiler last year with a condensing boiler. My gas bills have dropped by 30 - 40% (Â£300 per year).

It was well worth it.

tim oakley, uxbridge,

Run your car or boiler of water. We are not allowed to. The government have banned it.

Flatroofer, Crossgates, Wales

For efficiency the condensing boiler is a must. They are not complicated. The condensate does not require a soakaway and the venting is not that much different from a normal boiler. I have a feeling that those giving quotes may be "working the system". Mine has been running for years with no issues.

John P, London,

I obtained a couple of quotes to see if it made sense to replace my 20 year old gas boiler with a condensing boiler.

For my medium-sized four bedroom house, both quotes were Â£2500 for the boiler, a "plume vent" and a soakaway for the condensate. I calculated I had no chance of a payback because the efficiency of my old boiler is c.80%., a new one is not much more, at c.90%, but condensing boilers are complicated, have expensive components and are less reliable and durable. They require annual services at up to Â£100 or so.

Mike WX, Stratford,