How old is your central heating boiler?
If it’s more than 10 years old, it may be time to think about replacing it with a new high efficiency model.
Building regulations stipulate that if you are replacing an old boiler the new appliance must be A-rated for energy efficiency. This means it must be at least 88% efficient (most new boilers score over 90%), and to reach this level it will almost certainly be one of the new-style condensing boilers.
The technical bit
Condensing boilers are more efficient because they extract the heat from the exhaust gases (or ‘flue gases’) that all boilers produce. What makes this possible is a second heat exchanger where the water vapour in the flue gas condenses into droplets of liquid water, releasing heat as it does so. The condensed liquid water drains away through a pipe installed specifically for this purpose. Non-condensing boilers simply expel the gases into the air and the heat is wasted.
You’ll notice that the vapour that comes out of a condensing boiler’s flue forms a visible plume of ‘steam’ (actually a mixture of water vapour and other gases). This is perfectly normal and is an indication that the gases are cooler than those vented by non-condensing boilers.
Condensing boilers come in both combination and regular models. A combination (or ‘combi’) boiler will provide your central heating and produce hot water on demand, firing up when you turn on a hot tap in the kitchen or bathroom. A regular boiler will do your central heating, but rather than produce hot water as and when required, it will heat a quantity of water which is held in a storage cylinder until required.
Some boilers only run the central heating and don’t provide hot water at all, in which case an electric immersion tank or another form of water heating is required.
In a typical semi-detached property that uses mains gas for heating you can reduce your heating bills by around £300 per year if you upgrade from an old G-rated boiler (less than 70% efficient) to a new A-rated condensing boiler with full heating controls (e.g. timer/programmer, room thermostat and thermostatic radiator valves).