What on earth is a boiler? Here we define what they are and explain exactly how they work.
While the domestic gas boiler was invented way back in 1868, it was not until the 1970s and ‘80s that gas central heating became commonplace throughout the UK.
Prior to the rise of gas heating, wood and coal fires were frequently used to heat homes.
Of course, other types of boilers exist such as oil and electric boilers, which we’ll also discuss today.
Despite gas central heating is the norm in the 21st century, what exactly is a boiler and how does it work?
Let’s dive in!
Introduction to Central Heating
Before defining a gas boiler, we should touch on central heating.
The boiler generates hot water which can then be pumped around pipework to a) fill and heat radiators and b) go to use as storage for other uses, such as showering and doing the dishes.
What is a Boiler?
Put simply, a boiler is a closed vessel used to heat a fluid.
Despite its name, boiler water doesn’t generally boil.
After all, the internal temperature of domestic boilers tends to land between 60°C and 75°C.
Most British boilers rely on natural gas fuel which is supplied by the national gas grid.
Moreover, the majority of those boilers are combi boilers.
Here are some common boiler types based on fuel:
Gas boilers.
LPG boilers.
Oil boilers.
Electric boilers.
Biomass boilers.
Here are different types of gas boilers based on how they function:
Combi boilers.
Heat-only boilers.
System boilers.
How Different Types of Gas Boilers Work
You’re probably most interested in learning about the different components and elements of boilers and how they function.
If you want to know how another type of boiler works (based on the fuel used), skip to the next section.
Regardless of the boiler type, it costs about £0.05 per kWh to run a natural gas boiler.
Combi Boilers
A combination boiler combines a central heating boiler with a water heater. Both are contained in a single unit.
This contrasts with other boiler designs which come with an external storage tank/cylinder. As a result, combi boilers save space.
However, combi boilers only supply hot water on demand, not continually.
It costs about £800 to £2,300 to install a natural gas combi boiler.
Pros
Very efficient (usually 90% or above).
Relatively low running costs.
Compact and saves space.
Cons
Not well-suited for high water needs.
Can’t be used for power showers.
You can’t use various hot water appliances simultaneously.
Heat-only Boilers
Also known as a regular or conventional boiler, a heat-only boiler is a traditional approach to domestic heating.
Unlike a combi boiler, a heat-only option features a separate cold-water tank and a hot water cylinder to store water.
The feed and expansion tank of a regular boiler is used to add cold water so that the water levels can be regulated.
As soon as a heat-only boiler fires up, it sends hot water to the radiators or hot-water cylinder.
An immersion heater can also be added to a conventional boiler to offer backup access to hot water in case your boiler was to break down.
The average cost of a professional fitting a regular boiler is £700 to £2,800.
Pros
Various water supply outlets can be used simultaneously.
You can have an immersion heater added if you like.
Cons
Uses up more space than a combi boiler.
Not the most energy-efficient option.
How much hot water you can use depends on how large the cylinder is.
System Boilers
If you have an especially large home with substantial hot water and heating demands, you should consider a system boiler.
A system boiler comes with a separate water storage cylinder, meaning that it can provide a property with a continual supply of hot water.
So, what is the difference between a system and a regular boiler?
Well, while a heat-only boiler maintains pressure with a feed and expansion tank, a system boiler does this with a pressurized heating circuit.
The circuit is topped up using mains water. You’d likely pay somewhere between £800 and £2,700 to have a system boiler fitted.
Pros
Can meet the high demand for hot water/heating.
Heats a property fast.
Better water pressure than a regular boiler.
Cons
No instant hot water.
Use up plenty of space.
How Other Boilers Work
But what if you don’t want a gas boiler? You may also want to know what other boiler types are and how they function.
LPG Boilers
Unlike natural gas boilers, these boilers are fuelled by liquid petroleum gas (LPG) which is housed in a storage tank.
It costs £0.07 per kWh to run an LPG boiler. Depending on the type and brand of LPG boiler being installed, you’d likely pay anywhere between £2,000 and £6,000 for the installation.
Unsurprisingly, an LPG boiler functions similarly to a natural gas boiler. It burns LPG to generate the energy required to heat water.
This water can then be distributed with pipework for heating and hot water uses. Of course, the key difference is how the gas is stored and the type of gas used.
Pros
Reasonably compact system.
More eco-friendly solution.
Cons
More expensive to run than a natural gas or oil boiler.
You need space to safely store LPG.
It’s up to you to resupply your LPG storage.
Related heating/energy guides:
Oil Boilers
Again, an oil boiler is fairly similar to a natural gas boiler. It’s mostly a difference in the fuel type being used.
Despite being a lot less common, still, about four million homes in the UK use oil boilers.
The oil is ignited inside the combustion chamber while a heat exchanger generates hot water.
If you have an oil combi system, the water is taken from the mains before being heated up or if you have a conventional oil boiler, it will be sourced from a cold-water tank.
Interestingly, the running costs of an oil boiler is about £0.05 per kWh, meaning it’s pretty much the same as a natural gas boiler.
It generally costs somewhere in the region of £2,500 to £5,000 to have an oil boiler installed.
Pros
Highly efficient, similar to a natural gas boiler.
Very quiet type of boiler.
Relatively low running cost.
Perform well during the winter.
Cons
Oil storage tanks use up plenty of space (so of course, you’ll need sufficient room to safely house such a tank).
Not as environmentally friendly as LPG.
Electric Boilers
If you want the most eco-friendly solution, consider an electric boiler.
Of course, for it to actually prove better for the environment, it’s important that the electricity used to fuel your boiler is sourced from a green source.
Popular green energy providers in the UK include Ecotricity, Octopus, Green Star Energy, OVO Energy, and Outfox the Market.
Put simply, electric boilers heat water by running it over a heating element which is powered by electricity.
One of the main advantages of an electric boiler is that they bring no risk of carbon monoxide poisoning or any gas leak for that matter.
This, of course, assumes that you have your old heating system’s infrastructure fully removed to bring the risk down to zero.
However, the running cost is high, at around £0.16 per kWh. It costs approximately £1,500 to £3,000 to install an electric boiler.
Pros
Zero carbon emissions if you source electricity from a green provider.
Generally easier to install.
Low noise output.
Cons
Expensive to run.
Not suited to a large home.
Would use up most of your home’s energy use.
Biomass Boilers
A biomass boiler is a heavy-duty solution to your heating needs.
It generates heat to warm up water by burning organic materials (e.g., Plants, wood, and biological waste) in a combustion chamber.
The heat generated is then used for heating and hot water needs. In some cases, a buffer storage will be used to hold on to some of that energy for later use.
It also only costs about £0.04 per kWh to run a biomass boiler.
However, you’d need to refill your boiler on a regular basis manually and the leftover ash will need to safely be removed after the organic material is burned.
Not only that but it usually costs about £5,000 to £15,000 to have a biomass boiler installed in the first place.
Of course, a biomass boiler would only make sense for some homeowners with particularly high energy demand.
Sometimes biomass boilers are used to heat several homes.
Pros
Low running costs.
High energy efficiency.
The materials used to power a biomass boiler make it relatively eco-friendly.
Can meet especially high energy demand.
Cons
Requires manual refuelling.
Sufficient space is needed to safely run a biomass boiler.
Expensive to purchase/install.
Regular upkeep is required.
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