What types of central heating systems are available?

Central heating systems broadly fall into one of the following types:

  • ‘Wet systems’ involving a boiler/heat exchanger and radiators
  • Warm air system
  • Storage heaters​

Wet system

With a ‘wet system’ hot water circulates through a system of pipes that connect to radiators throughout a house. At the centre of the system, a boiler burns a fuel – or sometimes there is a ‘heat exchanger’ and this heats the water that feeds the network of pipes. ‘Wet systems’ are the most popular form of heating system in the UK.

​Radiators, despite their name, do not just give off radiant heat, in fact they deliver most of their heat through convection; air warmed by the radiator naturally rises, and cool air falls relative to it, as a result the warmed air circulates and the ‘space’ in a room is increased.

The pipework may also be connected to a hot water cylinder (tank), which will provide a supply of hot water for bathing and washing.

‘Wet’ central heating system.

Warm air system

Warm air systems were sometimes installed in the sixties and seventies in the UK, but continue to be popular in North America. Air is heated by a boiler, typically fuelled by natural gas, and fed via ducts to rooms around the home. The warm air enters the room via a floor or wall vent.

In commercial buildings, variations on warm air systems are still in widespread use, although they typically also serve as a cooling (air conditioning) system. In most homes, warm air systems have been replaced with ‘wet’ systems, which are generally more comfortable and efficient.

Warm air heating system duct.

Storage Heaters

The principle of a storage heater is that it contains ceramic bricks capable of storing large amounts of heat. These are heated overnight using off-peak lower cost electricity on Economy 7 or Economy 10 tariffs. The stored heat is then gradually released the following day.

​Facts

  • Storage heating systems consist primarily of individual storage heaters, typically they rely on a separate wiring system within the home for cheaper off-peak (Economy 7 or Economy 10) electricity, so can still be described as a ‘centralised’ system. The same wiring may also be used to heat a hot water cistern (tank).
  • A storage heater normally has at least two controls, one for controlling how much electricity is used, which will determine how much heat is generated for storage, and another for controlling how much heat is released. This means that if you’re out during the day, you can delay the release of the heat until you return in the evening. More advanced storage heaters also have thermostatic controls.
  • Unlike older storage heaters, which took up a lot of space, modern units use bricks with much greater heat storage capability, and are far more streamlined.
  • In some cases, storage heaters can also serve as direct electric heaters, providing heat directly from electricity without going through the storage stage, however they will typically use peak rate electricity which is more expensive.
  • Often homes relying on storage heaters will also have separate electric heating systems to supplement heating needs; invariably these will use peak rate electricity and are very expensive to run.
  • Example of power used by a storage heater in a room that requires 1kW of heat.
    –  Requires a storage heater that consumes around 3.2 kW per hour.
    –  Economy 7 tariff = 7 hours electricity at a cheaper rate during the night.
    –  Storage heater consumes 3.2kW per hour for 7 hours = 22.4kW per night (around £3.15 per night).
    –  Releases 22.4kW of heat consumed over a 24 hour period = heat output of 0.933kW of heat per hour.

This means that storage heaters are efficient, in that they give out all the energy that they consume, however they consume a lot of energy and as such are very expensive to run.

Benefits

  • Electric night storage heaters are much cheaper to install than gas central heating systems as they don’t require pipe-work or a flue.
  • With very few moving parts, storage heaters need very little maintenance and don’t need to be serviced annually.
  • Unlike gas, mains electricity is available almost everywhere in the UK.
  • Storage heaters can offer a practical solution for many homeowners; for example, as the heat is released throughout the day, storage heaters are more suitable for people who are retired or at home all day.

Negatives

  • It is one of the most expensive heating options in UK and emits more CO₂ than most other systems.
  • If you work full time and do not require heating during the day, storage heaters may not be the best option as heat will be emitted even when you are not there, resulting in unnecessary energy wastage.
  • As storage heaters age, their internal insulation can break down; resulting in heat being expended too fast and so supplementary heating may be required for later on in the day.
  • Storage heaters are often deemed unattractive and the nature of their design makes them quite bulky protruding into a room.
  • The daytime rate on Economy 7 or Economy 10 tariffs is higher than on standard single-rate electricity tariffs, so while you’ll receive a cheaper rate for your heating, by running extra appliances during the day will cost more – particularly if you have to top up your heating with a secondary electric heater.

Typical storage heater.

Under floor heating

Facts

  • Underfloor heating can be  a ‘wet’ system that pumps warm water through pipes under the floor, or a ‘dry’ system of electric coils placed under the floor and uses the basic principle of heat rising.
  • It is similar to installing a traditional central heating system, both in price and in process but think of it as like having a large, horizontal low-temperature radiator mounted in the floor. It may be expensive to install but in the long term can be cost effective.
  • In UK it is relatively rare whereas in Germany and Scandinavia it is the norm

Benefits

  • Like the best high-end fitting, underfloor heating is hidden away and out of view, doing away with the clutter of radiators.
  • And, due to the even distribution of heat, it is a fairly efficient way to heat a room. Compared to traditional radiators, underfloor heating works at a lower temperature and requires up to 33% less energy, so can save you money every year.
  • Because radiators heat up the area immediately around them, this ends up being quickly dispersed upwards, and away from the desired area. On the other hand, a good underfloor heating system will heat a larger area more evenly

Negatives

  • One of the biggest downsides is cost – not from the system itself but from the cost of underfloor heating installation – making them particularly suitable for new-build properties or when you are already having work done on your floor.
  • Due to the lower temperatures, an underfloor heating system will take longer to heat a room, so it is vital to combine it with a timer.
  • Be careful what you stand on the floor e.g Plants or certain furnishings may be adversely affected.

Grants

Underfloor heating pipes before overlaying with wood floor.

District heating

Facts

  • District heating involves the supply of hot water through hot water mains to homes and businesses – the hot water feeds into the domestic pipework to warm radiators and provide hot water in the home. It eliminates the need for an individual boiler in the home, but a heat exchanger is required.
  • Popular in northern and eastern Europe, examples of district heating schemes in the UK are currently limited (Nottingham), but more are likely to be constructed over the next few years.

Benefits

  • District heating uses large centralised boilers that can also generate electricity. Therefore, the cost of both the electricity and heat can be reduced, and carbon emissions are considerably reduced as well.
  • Provides a means of securing significant reduction in CO₂ emissions through the optimisation of heat supply.
  • Extends the reach of renewables, by using renewable heat efficiently and providing opportunities for the use of renewable technologies that otherwise wouldn’t be viable.
  • Improves security of supply.

District heating diagram (image: MTS Contracting)

Immersion heaters

Facts

  • An immersion heater is an electric water heater that sits inside a hot water cylinder. It acts a bit like a kettle, using an electric resistance heater (which looks like a metal loop or coil) to heat the surrounding water.
  • Most households will use a combined central heating/hot water boiler to heat their home and provide hot water, however If your boiler breaks down immersion heaters will still generate hot water for your home
  • Immersion heaters are connected to their own power supply via a cable. They can be switched on and off, as there’s no need to constantly heat the water in your hot water cylinder. Immersion heaters can either be used as a property’s primary water heater, or can be used as a backup water heater for combi boilers.
  • Immersion heaters are an expensive way to generate hot water and yet some households, particularly those with older heating systems, use immersion heaters as their only source of hot water.

Benefits

  • If your immersion heater has a thermostatic control, it will automatically turn off when it reaches the temperature you set on the thermostat.
  • Immersion heaters are not connected to your boiler. So if your boiler breaks down, you can still generate hot water for your home.
  • If your immersion heater has a well-insulated jacket, it can keep water hot for several hours after it switches off.
  • Time-of-use tariff customers can set timers so their immersion heater switches on during cheaper off-peak hours.
  • You can usually turn your immersion heater on or off by simply flicking the switch on the wall socket.
  • If you currently generate electricity for your home from solar panels or a wind turbine, you can now divert some of this electricity that isn’t being used in your home to your immersion heater. This means you can heat your water free of charge. This will require a small gadget available from several companies costing around £250.00. In addition electricity generated from renewable energy sources qualifies for financial help from the government under the ‘Feed in Tariff Scheme’. Unfortunately the government has recently cut this tariff which reduces the incentive to purchase a system.

Negatives

  • Heating water using electricity is more expensive than heating water with gas.
  • A typical immersion heater uses 3 kilowatts of electricity an hour, so it will cost the average house about 40p an hour to run.
  • Most households will need to run an immersion heater for at least a couple of hours a day to get the water hot enough – costing at least £290 a year.
  • An immersion heater needs a thermostatic control, otherwise the water temperature can rise too high.
  • Some heating engineers may recommend you leave your immersion heater on 24/7 – however, this can be hugely expensive unless it has a thermostatic control.
  • Be aware that you need to heat the water in your immersion heater to above 65°C to kill off bacteria.

Immersion heater diagram

​Rayburns

Facts

  • One of the most common misconceptions about Rayburns is that they have to be ‘always on’, however today’s Rayburn ranges includes many models that offer total, independent and programmable control over cooking, heating and hot water – so that every user can tailor the use of a Rayburn to suit their own lifestyle.

Benefits

  • In terms of the fuel and heat efficiency of a Rayburn, their post-war origins ensure that they do as much as possible for as little as possible. The use of cast-iron is designed to hold onto heat, and let it trickle out slowly to the home whilst cooking.
  • Engineering and technological advances in the intervening years have greatly added to this basic benefit: Rayburn boilers are now highly rated for their energy efficiency and fuel use
  • When a Rayburn is used for cooking, heating and hot water, it operates at a level of fuel efficiency that equals – and sometimes betters – the separate provision of these functions. When you also factor in the ‘AGA effect’ of radiant heat that a Rayburn brings to the kitchen, you have an ancillary energy source that can replace the output of a conventional radiator. This can be used for everything from drying clothes and warming food to incubating farm animals or preparing dried herbs – at no extra cost

Rayburn

Gas fires and fixed gas heaters

When it comes to gas fires, the following options are available:

  • Open flame
  • Radiant
  • Glass-fronted
  • Flueless (catalyst)

Fires with a balanced flue are more efficient, because there’s no need for ventilation. Modern gas wall heaters are also available with balanced flues, which means they’re almost as efficient as modern central heating boilers. They don’t act as a focal point of a room like a fire would, so they’re a better option for halls, stairwells and kitchens where there is an outside wall close by.

Fixed gas heater