There are now three broad options for a boiler installation: conventional, combination and condensing. If you are considering a boiler replacement, it is worth understanding the differences and benefits of each.
Conventional boilers use a gravity heating system with a water tank in the loft. This is the traditional system whereby a store of water is heated up prior to you using it, via the hot water cylinder and header tank.This can be problematic as it comprises many large parts like the cylinder and header tank which require space for storage.
As the cylinder is heated whenever the hot water is on, the water can sometimes by very hot when it is required use. When the pump is off, the radiators can heat up by default due to convection. Therefore, whilst the conventional boiler does it job effectively, it does have some side effects that you must be aware of for safety reasons.
Combination boilers are a high efficiency option, and can involve condensing (see below). They also economise on space, and are currently a popular choice for UK homes. Combi boilers account for more than half the new domestic boilers installed in Britain annually.
Combi boilers are highly suited to small houses or flats because they don't store water; they simply heat it as you use it. There is no cylinder, no tank and no connecting pipe work, which saves space and reduces hot water costs.
You can therefore access hot water almost instantly 24/7.
This helps you save on hot water costs, as the hot water is fed at mains pressure. Combi boilers provide a powerful shower without the need of a pump.You can also save money on installation, as the time will be much shorter as there is less to install!
Condensing Boilers are modern and highly efficient, incorporating an extra heat exchanger so that the hot exhaust gases lose much of their energy to pre-heat the water in the boiler system. Water vapour produced from the combustion condenses into liquid form releasing the "latent heat of vaporisation". The condensate from this process has to be piped away.
From an energy saving perspective, it is always better to have a condensing boiler. There are more expensive, but it the long term will be cost efficient for the amount of energy they save.
Condensing boilers have been used the US and on the continent since the 1980s, but are still in a small number in the UK, largely due to cost but also due to a lack of information about the technology.
The cost of condensing boilers is decreasing though, as with all new technology, and the benefits will outweigh the cost.
It is possible to replace most existing boilers with a condensing boiler, whether they are floor standing or wall hung. Extending fluing can be added.
Finding a place for a condensing boiler is no harder than placing a conventional boiler, the only addition is the condensate drain.
You can purchase a standard or combination boiler, and they are no harder to install than any conventional boiler. You will not need to change your system design.
It is not a requirement to install oversized radiators to achieve energy efficiency. The main energy benefit is from having the larger heat exchanger. While large radiators create lower return temperatures and do add efficiency, the extra benefit has not been regarded as cost effective.
A high efficiency boiler requires good heating controls. Ensure you have:
- an electronic timer or programmer
- a room thermostat
- thermostatic radiator control valves (TRVs)
- separate thermostatic control on the hot water system