Donnachadh McCarthy: The Home Ecologist

"You are not seriously asking me to turn off the heating in my little boy's bedroom, are you?" Such was the plea from an anxious mother as we worked our way around her home for an eco-audit.

We'd already checked the roof to see if it had potential for solar electric panels, and we had progressed to looking at the insulation in the quirky roof-space above her son's bedroom. Her horrified question came after I asked when her son would be home, and she replied that he was away at boarding school. I suggested turning off the radiator and closing the door, and she gave the answer I've quoted above. When she heard herself say it, she immediately realised the silliness of what she had just said, and we both burst out laughing.

People make some strange decisions about when, and in which rooms, they need their heating switched on. I never tire of repeating the mantra that we can cut up 40 per cent of our domestic carbon emissions by tackling wasteful lifestyles. And one of the biggest allies in doing just that is not some hi-tech gizmo. It's the humble door.

In the Fifties it was perfectly normal to heat the room that we were in and to turn the heating off and close the doors of all other rooms, except for an occasional airing. Nowadays we heat the whole house just in case we want to use the bathroom, or pop into the bedroom or home-office to check our emails. We simply cannot afford to do this any longer. Unfortunately, architects have supported this trend by designing open-plan homes with almost no internal doors at all. These require the home-owner to heat vast unoccupied spaces.

In addition to being a crucial ally in reducing carbon footprints, doors can also be an enemy. I recently eco-audited a lovely new home in Berkshire, which had masses of wall insulation and double glazing throughout, but the front door was a disaster. It was so badly fitted that I could see daylight through all the gaps. Through the keyholes blew a bitterly cold draught, and the letter box, likewise, was a joke.

Up to 20 per cent of our heat can be lost through badly insulated doors and windows. The recipe for a cosy door has five ingredients: strip insulation along the sides and top, a door-brush at the bottom, a keyhole flap or draught-proof lock, a properly draught-proofed letter box and (for the gold-standard) a beautiful, thermally lined door-curtain. Ideally, outer doors would also have a lobby with a second inner door.

It is not just the outer doors that need such cosy treatment, however. People often forget that doors down into cold basements, or hatches and doors into unheated loft-spaces, are the equivalent of an external door and if they are not draught-proofed they will lose you a lot of expensive heat in winter.

Having seen the funny side of her subconscious mind preventing her from turning off the heating in her son's room, that client proceeded to turn off the radiator, and close the door to his room. How many rooms are you similarly heating in vain?

If you stop, you'll slash your bills – you might even be able to reduce the room-space being heated by up to 90 per cent. And that'll be a benefit both for your wallet and the planet.

Donnachadh McCarthy is author of 'Saving the Planet Without Costing the Earth' and works as a commercial and domestic eco-auditor, www.3acorns.co.uk