What types of boilers are there?

Most homes nowadays contain some kind of boiler to heat hot water as well as the water that runs through our radiators to provide us with central heating. In this article we take a closer look at the types of boiler systems that are available to us, which ones best suit which types of home and lifestyle, as well as how to go about selecting the right one for you from the various types of central heating boilers on the market. 

What types of boilers are there for heating and hot water?

There are three main types of boiler systems: combi boilers, heat only boilers and system boilers. We take a look at each of these three in turn below.

Combi boilers

Combi is short for combination and is a type of boiler system that combines central heating and on-demand hot water within the same unit. This extremely compact unit can be powered by mains gas, oil or LPG, and works through the use of heat exchangers which transfer energy from the sealed combustion chamber into mains water. 

Combi boilers generally have two heat exchangers, the first of which heats the water that goes into the radiators and is subsequently recycled back into the boiler. A thermostat monitors the system temperature and turns the boiler on when needed in order to keep the water at the specified temperature. The water from the radiators is potentially contaminated, so the second, isolated, heat exchanger is used for on-demand hot water. Mains water is pumped through it, delivering hot water to your taps as you require it. 

Heat only boilers

Heat only boilers burn fuel to heat water and distribute it using a system of valves, pumps and tanks. They are also known as regular or open vent boilers as they are not pressurised. 

Heat only boilers require a cold water storage tank connected to the mains, usually held in the loft. A feed tank holds water taken directly from the cold water tank and feeds it into a hot water cylinder. The boiler burns oil, LPG or gas to heat the hot water cylinder, and the hot water is then pumped or gravity fed to outlets when needed. A pump also circulates heated water to radiators when the heating is turned on. A heat only boiler will also have an expansion tank, which, in combination with the feed tank, maintains a consistent water level in the system. This controls losses from leaks or evaporation.

System boilers

System boilers are a type of boiler used for both central heating and hot water and it works in much the same way as a heat only boiler, except that it doesn’t have the cistern – or cold water tank – in the loft. 

This is advantageous for two main reasons; firstly, you don’t require the space to hold a cold water tank in your home and, secondly, because the cold water feed is taken directly from the mains, water pressure in system boilers is generally much better than in heat only boilers. 

Which types of boiler systems are suited to which homes?

Combi boilers do not require a cold water tank, an external hot water cylinder or a feed and expansion tank, which means they take up much less space in a home. This makes a combi boiler a much better option in smaller properties where space is at a premium. However, they don’t cope well in delivering hot water to multiple points at once and so tend to struggle with larger properties where there are multiple hot water draws. 

Despite having a much larger footprint, the advantage of a heat only boiler is that it can supply water to multiple outlets simultaneously as the hot water tank can store large volumes of hot water and deliver it instantly. This makes it ideal for large properties with multiple bathrooms. Because of the cistern tank, they are also ideal for properties in areas with low water pressure. However, the heat only boiler has a finite amount of hot water which is limited to the size of your hot water tank, and you then have to wait for the boiler to heat a further tank of water for use. 

System boilers are more compact than a heat only boiler though do require more space than the combi boiler option. They are capable of delivering hot water to multiple taps simultaneously and, provided the mains pressure is good, offer better water pressure than heat only boilers. However, they do require programming to heat the water in advance of when you need it because they are unable to heat water on demand like a combi boiler. System boilers are more cost effective than heat only boilers to both install and to run. 

Choose your next boiler from toasti

toasti are able to supply all three types of central heating boilers and partner with some of the best manufacturers on the market, including Ideal and Worcester. Our qualified heating engineers will be able to advise you on which types of boiler systems would best suit your home, and what would be required in terms of boiler installation. For advice that you can trust, get in touch with the friendly team at toasti who will be happy to talk to you in more detail about the type of central heating boiler that would best suit your family.