What type of gas boiler do I need?
All modern gas boilers installed today are condensing boilers, of which come in one of three types: conventional, system or combination.Condensing boilers are up to 90% efficient as heat is recovered from flue gases that otherwise would have been lost like on older less efficient models. A modern gas boiler maximises fuel efficiency by extracting latent heat from flue gases utilising a condensing system.
The condensate water (which is acidic) is drained away to a suitable waste. You can identify a condensing boiler as it will have a plastic waste pipe. These waste pipes can freeze in cold weather and stop the boiler from operating until the pipe has thawed. When replacing old boilers the additional requirement of a waste pipe can be a problem, however condensate pumps can be used in awkward areas.
The type of boiler installed will depend on the type of system you have installed and whether or not you’d like to change the central heating system you have. For example upgrading from an old system to a modern one. Of the three types a combination (also known as a combi) boiler is arguably the most popular, a combi boiler is responsible for both the heating and hot water requirements of the household, hot water is heated on demand when a hot tap is opened. This means it is the most space-saving as there is no requirement for a hot water cylinder, unlike conventional and system boilers which both require a cylinder to store the hot water. Hot water cylinders are usually housed in areas known as airing cupboards. Most gas boilers you buy today are so compact they will fit in a kitchen cupboard.
Slowly becoming obsolete conventional boilers (also known as heat only and regular boilers) are designed for older systems where header tanks are positioned in the loft. An external pump circulates water around radiators and the coil within the hot water cylinder. These systems are the most awkward to install and the technology has been superseded. The drawbacks are low water pressure on the hot water taps and sludge build up in the radiators which can cause pumps, motorised valves and the heat exchanger on the boiler to block up and eventually fail.
The modern equivalent to a conventional heating system, a system boiler is designed to be used with modern radiators and unvented hot water cylinders. Instead of header tanks the system is a pressurised closed loop and is filled by means of a filling loop connected to the cold water supply, expansion vessels are used to absorb rises in system pressure when the water expands during the heating process. Hot water is mains fed so will be at the same high pressure as your cold mains and can satisfy the hot water demands of a large household. The circulating pump is located inside the boiler and the heating and hot water is controlled by a programmer, room thermostat and cylinder stat. One benefit of stored hot water is should the boiler breakdown you can use the immersion (electrically heated element) as a stand by until the boiler is fixed. One drawback is these systems are complex with a number of components working in harmony, this means they are costly to install and maintain.
Popular with both householders and installers combi boilers satisfy both hot water and central heating requirements of the household without the need for hot water cylinders or external pumps and valves. A modern combi boiler is usually designed to fit in a kitchen cupboard and can provide hot water on demand at mains pressure. The system is easier to control as all that is required is a programmable thermostat, times are not required for hot water as it’s heated only when it is needed. This means the hot water will never run out. However there are disadvantages, combi boilers are designed for small to medium households, water pressure drops when two hot taps are used at the same time. A combi system is a pressurised closed loop, operating pressure should be between 1 and 1.5 bar displayed on the pressure gauge.