Doctor On The House: Flue, what a scorcher: the hot thing in heating

NOW THAT summer has finally arrived, it's time to start thinking about the central heating. If you've been planning a new boiler, or moving a couple of radiators, you've got more chance of engaging a decent plumber at this time of year. And, if unexpected problems should arise, it won't be a disaster to be left without heating for a day or so.

The best way to save money on heating this winter, as every pensioner knows, is to spend all your waking hours in the public library. Probably the worst way is to buy replacement double-glazed windows; studies have shown that the small amount of heat they save is unlikely ever to cover the cost of the installation.

Somewhere in between come condensing boilers. These are being promoted by the green lobby - and, of course, the manufacturers - as the latest in energy efficiency, but Steve the plumber is not so sure.

Condensing boilers take almost all the heat out of the burning fuel, so the flue gases are cool. This results in condensation within the boiler, hence the name. When they're up and running, condensing boilers are reckoned to be around 15 per cent more efficient than conventional ones, but Steve's scepticism comes from the fact that they are more complicated, so there are more parts to go wrong and need replacing. Because they need much more diligent servicing, maintenance costs can be double those of conventional boilers.

For example, the condensed liquid, which is corrosive, has to be piped away to the drains - and these pipes must be regularly checked for blockages.

Condensing boilers also have a characteristic that is never mentioned in the brochures. Because the flue gas is cool, in cold weather it actually emerges as steam.

Plumbers call this pluming, and it means you get a jet of steam coming out of the balanced flue in the outside wall. If your house is on its own then nobody will mind, but Steve says that in some parts of bedsit land the steam from these plumes can now be seen shooting in through the windows of the people opposite.

In condensing boilers the heat exchangers are aluminium, so they would be more expensive if it were not for grants from the Energy Saving Trust - an industry and government-funded body - to persuade householders to replace their old systems with condensing boilers. Nothing wrong with that, if the aim is to lower the nation's fuel consumption, but as with other supposed energy-saving schemes, there is a danger that such a subsidy may mask the true energy costs.

Aluminium, for example, uses an enormous amount of power in its manufacture, and Steve's multiple visits to service and fix the boiler will themselves use up some of the earth's resources - petrol, wear and tear on the van, getting the spare parts shipped over from Germany, bacon sandwiches consumed on the job.

It all depends on how you look at it, but perhaps this subject needs a bit more thought before we all jump blindly in.

q Contact: Energy Saving Trust, 0345 023005.

q Jeff@doctoronthehouse.demon.co.uk