Frequently Asked Questions about industry terms from Columnrads UK.


A Joule is a defined measurement of a unit of energy, that is used in a range of application, including thermal energy. In the heating industry, it is more common to use British Thermal Units (BTU). One BTU can be thought of being around 1,055 joules.


A timer is used in heating systems to control when your heating, or hot water system is switched on. Typically, a timer allows a user to create a programme to switch on the heating system at certain times at the day. This device is used to help save energy and money.

Celsius (°C)

Celsius is a metric scale for temperature, and is also known as centigrade. The degree Celsius (°C) is a measurement device that can be used to reference a temperature on the Celsius scale. The Celsius scale is based on 0° degrees for the freezing point of water and 100° degrees for the boiling point of water at 1 atm pressure.

Bar (pressure)

A Bar is a measurement unit that is used to measure pressure. One bar is generally about equal to the atmospheric pressure on Earth at sea level. In relation to heating systems a bar references the pressure that a heating system runs at. Understanding at what pressure your heating system runs at, and how to adjust it is important.


A radiator is a heating devices that allows hot water to circulate through, which it turns heats the surrounding area by radiation convection.


Heat flux or thermal flux refers to the rate that heat can transfer through one material to another material over a given time.

Tank (expansion)

An expansion tank is a device fitted to central heating systems that is designed to protect the system from excessive pressure. Water hammer and excessive pressure can be the cause of problems in a heating system. Expansion tanks are partially filled with air, and this air is compressed, to help alleviate these thermal expansion issues.

National Grid

The National Grid refers to the power network in Great Britain and is a system by where power is distributed from power stations to consumers using power lines and wires. Nearly every home around the UK is connected to the National Grid.

Underfloor Heating

As the name might suggest, underfloor heating is a form of heating that is located under the floor in a building. Generally, there are two different types of underfloor heating, water-based underfloor heating that connects to a traditional central heating system, and alternatively, electricity powered underfloor heating, which runs by electricity alone. Typically water-based underfloor heating is more expensive to install, but is cheaper to run when compared to electrically powered heating.

Jacket (tank)

A tank jacket is a form of insulation that is wrapped around a water tank to reduce thermal transfer between the tank and the surrounding air.

(Lime) Scale

Lime scale is a hard, chalky deposit found in kettles and water pipes of central heating systems. Lime scale is made of calcium carbonate and hard water typically contains calcium. Over time lime scale deposits can build up and compromise the system. Descaling agents are available to help remove lime scale, in addition to this water softening products can be used to help prevent lime scale.


Alpha are a manufacturer of central heating boilers and they supply a range of combi boilers with a ten year warranty.


Benchmark is a national scheme that is managed by the Heating and Hotwater Industry Council (HHIC) that aims to ensure best-practice for the installation and servicing of hot water and domestic heating.

Combination (Combi) Boiler

A combi boiler is a type of boiler that combines both your central heating system boiler, with a hot water boiler. The reason for having a combi-boiler is to save space in a property since a separate water cylinder is not required.


A radiator reflector is a foil-like material that is placed behind a radiator to 'reflect' heat back towards the house. The reason a reflector may be useful is when a radiator is attached to a single skin wall and heat is lost through the wall, to the outside of the building

Risk Assessment

A central heating risk assessment is a document provided by your installers detailing the full work sequence of your installation, potentially covering areas such as installation of a new boiler, running of pipe work, general radiator fitting and ensuring the system is working correctly using the correct procedures, methods and tools.


A boiler is a device in a central heating system that is used to heat water. There are different types of boiler available. Combi boilers are a type of boiler that is used to heat both hot water and the central heating in one device. System boilers require a hot water storage tank but can be used to save space, since a cold-water tank is not required. Regular boilers, or traditional boilers require both a hot water and cold water storage tank. Ultimately, boilers all do the same thing, which is to heat water, either for heating, or for hot water supply to the taps in a home.

Building Regulations

Building Regulations, or ‘building regs’ for short, are a set of standards and requirement set by the United Kingdom government which details the minimum requirements for building design and construction.

Carbon Monoxide

Carbon Monoxide is a poisonous gas, that is odourless and cannot be detected by human senses making it a potentially lethal substance when concentrated in the home. There are many causes of carbon monoxide, but in the home, poorly installed, maintained central heating systems can be the cause of accidental exposure. Poor ventilation in the home, or blocked flues and chimneys can also cause a build-up of carbon monoxide. Proper maintenance of heating system can prevent issues with carbon monoxide, and it is also a good idea to install carbon monoxide detectors and alarms to alert you to any build up of carbon monoxide in the home.


Insulation is a product that is designed to reduce heat transfer from one material to another. The reduction in thermal energy loss means that less energy is wasted and in turn money is saved on your energy bills. Insulation can take many forms, from wall insulation to roof insulation. In terms of central heating systems, it is commonly found as pipe ‘lagging’, where insulation is wrapped around pipes to help retain heat and minimise heat-loss.

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