Central heating systems serve the same function of warming up a home or building, and many of them provide hot water through the tap. However, they can be diverse in terms of design, incorporating components such as boilers, vents, or even heat-storing bricks.

Each has its pros and cons, which are especially useful to know if you’re considering central heating installation and refurbishment. Here’s a guide that walks you through the three main types of central heating systems:

Wet Systems

Most homes in the UK have a wet system for central heating. Wet systems have a basic structure that consists of a boiler and a radiator. Typically fuelled by gas, the boiler heats up the water, which moves through pipes either under the floor or inside the walls of the home. The heat is then emitted through radiators, which spread warm air through the surrounding space. Wet systems can also warm up water coming from taps and showers. Afterwards, the water passing through the pipes returns to the boiler to be reheated, resulting in continuous heating.

Wet systems are usually fuelled by natural gas, which comes from a gas main outdoors. Some homes that don’t have access to this turn to liquid petroleum gas (LPG) or heating oil instead, which are more expensive. Natural gas has a low price per kilowatt-hour, so wet systems are a more affordable option.

The boilers in wet systems can also vary:

Combi Boiler

Combi boilers (or combination boilers) are the most common today. Unlike a conventional boiler, this heats up water instantly, right when you want it. Because it doesn’t need extra storage, the system design is minimalist and made up of only a few components. In fact, as the name implies, it only has one unit that does the job of warming up your home and producing hot water.

When you activate the heating, the combi boiler starts burning fuel, and the heat is instantly transferred to the water inside your home’s pipes. In other words, if you’re in the shower, you can get hot water as soon as you turn on the specific tap.

The main benefit of this compared to other wet systems is you save a lot of space and installation costs lower. On the other hand, it doesn’t store hot water, so you’ll notice a drop or lag in heating when you turn on two hot water taps at the same time.

Conventional Boiler

In old homes and buildings, you’re likely to find a conventional boiler. This used to be the standard for homes all over the UK, but it has largely been replaced by combi boilers now.

A conventional boiler has a much more complex setup. For one, it’s gravity-driven, so you have several pieces of equipment that have to be placed on a higher level, ideally in the loft. These include a cold water storage tank as well as another for hot water, while a water storage cylinder would be on a lower floor.

The cold water storage tank transfers water to the water storage cylinder, where it’s heated up. Next, the water goes to the hot water storage tank, staying here until it moves to the home’s radiators and taps. In addition, the system has an expansion vessel as well as a feed and expansion tank to maintain the pressure and water level.

One reason why this isn’t as widespread anymore is it takes up a lot of space because of the additional tanks and pipes. Because water keeps shifting from one container to another, there’s greater heat loss too. Still, conventional boilers can provide hot water to multiple taps, which combi boilers can’t do very well.

System Boiler

The design of a system boiler is somewhat halfway between that of a conventional boiler and a combi boiler. Like a conventional boiler, it can supply hot water to multiple taps at the same time. However, its main components only consist of a boiler and a hot water cylinder.

The boiler takes in cold water directly from the mains and heats this up. Once the water is hot, it’s stored in the cylinder until it’s needed. System boilers can be a great option for homes with multiple bathrooms as long as the flow rate and mains pressure are both strong. For lower pressure, conventional boilers work better. A downside of system boilers is they’re pricier to install and maintain.

Warm Air Systems

In offices and commercial buildings, you’ll notice a type of central heating called warm air system. These are already considered old-fashioned since they reached peak popularity in homes back in the 70s and 80s. Notably, they can provide both heating and air conditioning, and they can run on either gas or electricity.

A warm air system functions similarly to a wet system, in that the boiler warms up air and then circulates it around the building. The main difference, though, is that warm air systems use ducts and vents instead of pipes and radiators. You can control its air production through a thermostat.

This works very quickly so there’s little waiting time, and there’s extra space inside the building because it doesn’t use radiators. Still, warm air systems are more expensive, many models can’t heat up water, and they can be problematic for people with allergies because they can transfer allergens from room to room.

Storage Heaters

Storage heaters are an electric-powered central heating system. These consist of bricks that store energy at night to take advantage of off-peak electricity. When daytime comes around, the bricks release the energy, generating heat for your home. For each storage heater, you can usually set its electricity consumption, which determines how much energy is stored, as well as the amount of heat it releases during the day.

Compared to warm air systems and wet systems, storage heaters are much more convenient to install, and maintenance is minimal. However, the timing might not work for you if you’re not in your home during the day, when heat is released. It’ll also be colder at night because the storage heater will be focused on storing heat. Some storage heaters have more advanced controls where you can time the heat storage and release, but you potentially miss out on the cheaper energy rates at night.

There are other central heating systems available such as electric boilers and under-the-floor heating, but these are much rarer. For the most part, the three systems above are the most widely used. Wet systems are the default for central heating at home, while many commercial buildings still have warm air systems and storage heaters are mostly used by homes without access to gas.