Genuine, unbiased consumer advice on gas boilers
- Types of gas boiler
- How does it work?
- Fuel costs
- Boiler installations
- Best gas boilers
- Building regulations for gas boilers
- Frequently asked questions
GAS BOILER GUIDE
1) Types of gas boiler
There are three forms of gas-fired boiler:
The vast majority of gas boilers work with radiators (known as a ‘wet’ central heating system). Some gas boilers are floor standing and sometimes incorporate a small hot water cylinder that boosts the hot water flow rates. Gas boilers are available as wall hung combination, heat only and system boiler models. For more on the different boiler types, see our Guide to boiler types. 80% of boiler sales in the UK are combi boilers so we have devoted a section of our site to this boiler type. If you are buying a combi boiler you may wish to visit our Guide to combi boilers.
Warm air units
Warm air units heat the home by blowing warmed air around the house via a series of vents. These boilers were very popular in the 1970s and are still manufactured today.
Back boilers were popular in the 1960s. They are a form of heat only boiler but the flue goes via a chimney breast and they are nearly always accompanied by a gas fire on the front. It was possible to replace a back boiler until fairly recently, although newer models were accompanied by an electric fire on the front. Whilst they are no longer available (because they cannot meet condensing boiler standards) they can still be repaired. See our Guide to back boiler repairs, replacements and servicing for more.
2) How does a gas boiler work?
Gas boilers burn gas to heat up water in your radiators. A pump circulates the heat water around radiators. For warm air units a fan blows across the hot heat exchanger and expels warmed up air via the ducts and floor vents. Combination boilers also heat up potable (drinkable) water for washing and showering via heat exchanger. Heat only and system boilers work with a hot water cylinder to produce hot water for washing and showering.
Boilers usually work with some form of thermostat which sets the temperature of the home. From a basic dial room thermostats to sophisticated advanced smart controls, the efficiency of the boiler is directly related to the type and compatibility of the heating control fitted.
3) Boiler sizing
A 6-10kW boiler will comfortably heat the vast majority of UK homes on a very cold day. However gas boilers start at 11-13kW for heat only/ system boilers and 16-18kW (and higher) for combi boilers. It is clear that even the smallest boiler will heat the majority of UK homes, however that comes with a slight caveat for hot water production.
Combi boilers often appear ‘larger’ because they show outputs of 24kW and upwards, but this is for hot water production. For boilers that work with a hot water cylinder, hot water production is a factor for sizing, so you may need a larger boiler depending on your system set up. For more help try our Guide to boiler sizing.
4) Boiler efficiencies
All condensing gas boilers have the capacity to be 92-94% efficient, which is equivalent to A-rated, however achieving efficiencies in the 90s depends entirely on how well the rest of the system is designed and controlled. Actual average efficiencies in the home are nearer to 80%. Getting the central heating system design right is just as important as which boiler you pick. See our Guide to gas boiler efficiencies.
5) Fuel Costs
Mains gas is one of the cheapest fuels to buy for homes heating, at around 4p per kWh. The only cheaper fuels are coal and wood chip. Fuel costs however are a factor of fuel price and heating system efficiency. Gas boilers can suffer low efficiencies of between 60-80% if the boiler is old or new and set up poorly. The table below sets out the cost per kWh AFTER the boiler’s efficient
6) Boiler Installation
There are many things to consider when arranging a replacement gas boiler, starting with whether the time is right for replacement. We offer guides on every aspect of a boiler installation, from assessing the lifespan of the old boiler to arranging finance.
When to repair or replace?
When is a good time to replace your boiler? Many new boiler installations are ‘distress purchases’, in other words your boiler has broken down and needs replacing quickly. More often boilers can be cost effectively repaired and there are many good reasons to keep your old boiler going. For more guidance read our Guide to repairing or replacing.
Finding an installer
There are many national, local and online companies ready to replace your boiler as well as local sole traders. Knowing who to pick can be a struggle. We have a comprehensive Guide to the different types of installation companies to help you weight up the pros and cons of a national company verses a sole trader or a local family business verses a sub-contractor network.
In all cases, gas boiler installers must be Gas Safe registered and experienced in boiler installations. Fitting boilers is a different skill set to those that repair boilers so it’s important to find someone that specialises in this area. Our Elite Installer network has brought together the Top 1% of UK installers.
Paying for a new boiler
Cash, credit card, interest free ;or 'rent a boiler' schemes are some of the options to pay for a new boiler. We explore all the ways to pay in our Guide to boiler finance.
Boiler prices can be refer to the cost of the gas boiler or the cost of the whole boiler installation including parts and labour and it worth making the distinction. Sometimes it's difficult to compare quotes because parts and labour are not broken down. It is therefore helpful to also look at the cost of the boiler in order to understand where differences in installation cost might occur.
Boiler installation cost
Our Guide to boiler installation costs gives a great overview of boiler cost including labour and sundries for a range of scenarios.
For a bespoke installation price, go to our Boiler quote calculator. It’s completely free to use and no personal details are required to see the prices.
Stand alone boiler prices
If you just want to compare standalone boilers prices, we compare over 200 boiler model prices in our three comprehensive boiler prices guides: combi boiler prices, system boiler prices and heat-only boiler prices.
8) Boiler brands
The mainstream boiler brands include big names including Worcester Bosch, Vaillant, Baxi and Ideal as well as some lessor known brands also doing great work, such as Ravenheat, Intergas and Viessmann. You can find out more about them in our Guide to gas boiler brands
9) Best gas boilers
There are a range of great quality, technically advanced, boilers for all budgets. The key thing we look out for is how low the boiler can go down in kW. The lower it can go, the more efficiently the boiler can work all year around. The short answer is to check out our Best boiler guide.
10) Building regulations for gas boilers
Building regulations cover many aspects of a new boiler installation, including its efficiency, heating controls, flue position, boiler location, frost protection and condense pipe drainage. Go to our Guide on gas boiler regulations for more.
11) FREQUENTLY ASKED QUESTIONS
Which are the best boilers for 3 bed houses?
The vast majority of homes in the UK are 2 and 3 bedroom houses and often they have similar amount of floor space. We have given extra attention to 3 bedroom houses in our consumer guide: Which are the best boilers for 3 bed homes? The guidance will also guide owners of two bedroom homes.
Can I get an extended boiler warranty?
All boilers come with a minimum 2-year warranty, but most extend that to 3-5 years as a minimum. Most boiler manufacturers’ offer extended warranties but many do require that the installer is accredited with them. This means that the installer has undertaken additional training on their boilers and when they register the boiler you will get the benefit of a longer warranty period. For more on warranties jump to our Guide boiler warranties and guarantees.
Where can gas boilers be fitted?
It is common to find your boiler in the kitchen, utility, bathroom and sometimes a bedroom. Boilers can also be located in an adjoining garage or loft, however this can be less efficient as many boilers lose heat via their cases. Where a combi boiler has replaced a boiler with a hot water cylinder, the boiler is often relocated to the airing cupboard. For more scenarios and pros and cons try our Guide to moving your boiler.