Donnachadh McCarthy: The Home Ecologist

Sealing the flue of an old fire costs just £20 – AND it can seriously cool your gas bills

I have eco-audited homes that have spent a fortune on double-glazing. The same people have usually sealed the gaps around their front door and letter box, and their loft will have been treated to an extra-deep layer of insulation. And then we'll walk in to the living room, and I'll point to a huge hole that the owners will never have noticed. This hole will be leaking up to 15 per cent of the heat from the home. It happens more than you'd imagine. Why? Because these great big holes are chimneys.

Dining rooms, bedrooms and even kitchens can have fireplaces losing heat right through the winter. Hot air will shoot up any unblocked chimney into the cold outside. Many older Victorian homes have ornate metal chimney closers to stop this heat loss. But if the chimney is never used, seal it up permanently. If used only rarely, it would be worth installing a Chimney Balloon (www. chimney-balloon.co.uk). These are made from industrial plastic and come with a valve, so that they can be placed up the chimney and blown up to seal it. They block about 99 per cent of the air-flow, allowing a small amount through for ventilation. They cost just over £20 and come in various sizes, depending on how big your chimney is.

If you like to have fires regularly, a wood-burner would be worth considering, as they are up to five times more efficient and their installation means the chimney is sealed off. You also find open chimneys over coal-effect gas-fires. These not only lose up to 85 per cent of the heat up the chimney when burning, due to their criminal inefficiency, but when not in use large amounts of the central heating output will also disappear up the chimney. Rightly, we have legislation on the energy efficiency of new homes, so it seems strange that these fuel-hungry monsters haven't been banned.

There is an alternative to having an open chimney above a coal-effect gas fire, however; it is called a flueless gas fire. These have catalytic converters, which destroy all the poisonous carbon monoxide fumes, and in terms of heat output, they run at an extraordinary high efficiency rate of 100 per cent.

But flueless gas fires are not perfect. They still produce condensation, so are generally recommended only for centrally heated homes. The room also has to be a certain size and you need to have an air vent fitted. I got one some years ago and had condensation problems, until I had my wood-burner fitted to the second fireplace. I now use it very occasionally as a reserve heat source, if I do not have time to light the wood-burner. Because the wood-burner dries out the house nicely, condensation is no longer a problem. Like the wood-burner, the flueless gas fire means that the chimney is sealed up and eliminated as a source of heat loss, even when the fire is not burning. Visit www.burley.co.uk to see a great range of modern and traditional styles.

So, this week check all your chimneys to ensure that they are not creating unnecessary carbon dioxide due to wasted heat – or making a hole in your bank account with all the money you're spending on heating.

Donnachadh McCarthy is a home and organisational eco-auditor; www.3acorns.co.uk

d.mccarthy@independent.co.uk