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Witten by Bernard Morgan (Engineer) & Adam Apperley (Marketing). Published: February 12, 2024. Updated: February 12, 2024

Central Heating System Explained

Central heating system explained | Boilerhut

A central heating system is essential for maintaining comfort in homes. This is especially true during colder months.

The most popular type of central heating system in homes in the UK is a wet system. This is where water is heated up and pumped around radiators.

Dry central heating systems heat air which is blown around the home through ducts. ‘Dry’ systems are most popular in commercial buildings. In general they tend to be dustier and louder. They are popular in the US as they can be combined with air conditioning.

The other main type of central heat system is storage heating. These are electric-powered heaters in individual rooms. They use off-peak electricity overnight to heat firebricks. This heat is released during the day. They can take 2 days to heat up and cool down. This makes them very hard to control, especially in unpredictable weather.

Wet Central Heating System Explained

Wet systems consist of a boiler, possibly a tank or two, pipework, and radiators. They work together to distribute heat and hot water throughout your home. Understanding the components can help you make decisions about maintenance, upgrades, or replacements.

Central heating system explained | BoilerhutIn a wet central heating system, a boiler heats water, which is pumped around a circuit of pipes to radiators. Most modern systems use a two-pipe system where each radiator is in parallel and gets fed from the boiler. The flow and return are separate so all radiators get a feed of hot water and return water to the separate return pipe.

A single-pipe layout runs water from your boiler through the home and back to the boiler in 1 pipe. Each radiator is then spurred off this single loop. This means that as the water flows around the home, it becomes cooler. This is because the first radiator dilutes the hot water with cooled water.

With a single-pipe layout, you need careful balancing and larger radiators to radiate more heat into rooms. It’s also less efficient as cooler return water is mixed with hot flow water in the single loop.

Types of Boilers

  • System boiler: Includes a boiler, hot water tank, programmer and room thermostat. Hot water and heating can be controlled separately. Hot water is stored in a cylinder. They have internal pumps and a pressurised expansion vessel. They are sealed, which allows for pressurisation.
  • Conventional boiler: Includes the same parts as a system boiler but will also include an external pump and cold water header/expansion tank. The header tank, usually in the loft, provides the pressure for the system. These are open vent systems where the only pressure comes from the gravity-fed water.
  • Combi boiler: This boiler features a programmer and thermostat. It heats hot water using the secondary plate heat exchanger on demand without the need for a storage cylinder. The pump and expansion are internal.
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Central Heating Controls

  • Room Thermostat: Regulates home temperature by sensing the air temperature. This controls the heat produced by the boiler.
  • Thermostatic Radiator Valves: Mechanical thermostats fitted on radiators. They control room temperature by regulating water flow.
  • Programmer: A control panel for setting heating and hot water schedules. Types include digital/electronic and time clock programmers.
  • Boiler Thermostat: Controls the temperature of water in the boiler. Combination boilers have separate thermostats for heating and hot water.
  • Cylinder Thermostat: Regulates hot water in hot water cylinder. Set 60-65.

Types of Radiators

New radiators - Central heating system explained | BoilerhutWhen looking at a central heating system the radiators are pretty important. There are lots of designs available, but the main consideration is the heat that they give out into the room. The simplest radiator is a single panel, which has one area which contains water.

Moving up, you can add convection veins to the back to help distribute the heat. Then add another panel, and then another set of convection veins. K3 (or Type 33) radiators have three panels and three sets of veins.

The more panels and veins the radiator has the more heat it will put into a room, but they’ll also be more expensive.

Future-proofing your heating system

  • Viessmann Vitodens 100-W 35kW Combi Boiler - Central heating system explained | BoilerhutNew Boilers: New, highly efficient gas, LPG or oil boilers can be 98% efficient, reducing emissions and saving you money on your heating bills.
  • Air Source Heat Pumps: Efficient and environmentally friendly, can be paired with existing boilers in hybrid systems. But, heat pumps are very expensive to install and there are strict rules around the £7,500 government grant. Heat pumps are not well-suited to most homes. Major insulation, radiator and pipework upgrades may be required.
  • Biomass Boilers: These use renewable fuel, typically wood pellets, for heating and hot water. Unfortunately, they can be expensive to install and tend to create more emissions than modern gas boilers.
  • Electric Boilers: Electric boilers are efficient and environmentally friendly, suitable for smaller homes. However, they are expensive to install and run, as electricity is 3-4 times more expensive than gas. You may also need an electricity upgrade to a three-phase supply.
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When to replace your system

Consider replacing your system based on age, efficiency, and repair costs. Boilers typically need replacement after 10-15 years. Upgrading to a more efficient system can save on energy bills and reduce environmental impact.


Your central heating system is vital to your home’s comfort and energy efficiency. Understanding it helps you make better decisions about maintenance and upgrades. Consider future-proofing your system with new highly efficient gas, LPG or oil boilers or renewable energy options.

Do you need a new central heating system installed?

If you need a new or replacement central heating system installed, get an online quote (it takes less than 1 minute), and you’ll get an instant price. But why choose Boilerhut:

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