Condensing boilers - cost £1,000 to £3,000

Gas: 6p/kWh, CO2: 0.22kg CO2e/kWh; LPG: 8p/kWh, CO2: 0.26kg CO2e/kWh;     Oil: 6p/kWh, CO2: 0.33kg CO2e/kWh

Condensing boilers have a very high efficiency rate (90% or more), achieved by using the waste heat in the extract steam to pre-heat the cold water entering the boiler. They are so called because the heat is recovered from the steam produced during combustionand thus it condenses into water. This process makes a condensing boiler approximately 10% more efficient than a conventional boiler.
 
Due to various manufacturing and installation constraints, condensing boilers are best kept small and thus ideal for domestic installations.In the UK, all new gas central heating boilers have had to be condensing since 2005. In the early days, plumbers and homeowners complained about the reliability and initial costs of condensing boilers..Nowadays, costs have come down and the technology is as reliable as conventional boilers.
 
Condensing boilers might run off natural gas, LPG, or fuel oil.

Combi boiler or regular boiler?

A regular boiler heats up water when told to do so by its programmable control. Hot water is then stored in a tank for use when required, and heating is supplied directly by the boiler when requested by the timer/thermostat.
 
A combi boiler doesn’t require a tank, but switches on whenever hot water or heating is called for, supplying both demands directly – hence ‘combi’ or combination.

Regular boilers are more efficient since they heat in batches and are not constantly coming on and off – every time you open the hot water tap a combi boiler will fire up. If you’ve simply rinsed your hands or similar, the energy that went into the hot water that never actually made it out of the tap will be wasted. On the other hand, regular boilers require tanks, and although modern tanks are extremely well insulated, they will still lose some of the stored heat (and require space).
 
Since combi boilers don’t require a tank, they are great space-savers. They could be a good option for you if you have good mains pressure and little hot water demand..However, in a home with more than 1 bathroom, or low mains pressure, it would be advisable to go for a regular boiler. If you are replacing an old boiler, it’s probably best to replace like for like, although your heating engineer should be able to advise appropriately.
 
In terms of whether you’d be best to choose a combi or regular boiler, there isn’t currently a clear consensus, with opinions and empirical evidence varying greatly. It’s probably best to just go with the option you’re most comfortable with - although please do remember that you can’t have Solar Thermal/Free Energy without a tank, and you will need a separate pump to run underfloor heating with a combi.
 
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