Product definitions

Back boiler

A small boiler fitted at the back of the hearth of an open fireplace or in a room heater to provide  domestic hot water and sometimes to heat radiators within a dwelling.

Biomass

Biomass is biological material derived from living, or recently living organisms. In the context of biomass for energy this is often used to mean plant based material, but biomass can equally apply to both animal and vegetable derived material.

Boiler

A boiler is a box in which a controlled burn of fossil fuel is carried out and the heat produced is transferred to water.

Combi boiler or Combination boiler

This is the name given to a boiler that heats water instantaneously on opening a hot tap. There are no tanks in the loft and no storage cylinder. The water is fed from the mains so the water pressure is generally stronger. What is a combi?

Combined Heat and Power

Combined Heat and Power (CHP) is the simultaneous production of heat and electricity.  Using a reliable internal combustion engine fed from a single source of fuel, such as natural gas or LPG, a CHP system can produce usable amounts of both heat and electricity.

Controls

All boilers have controls that allow you to adjust the water temperature and space heating temperature (thermostat). Other controls the boiler may have are a water pressure gauge and a digital or electro-mechanical timer.

DHW

Domestic Hot Water

Expansion vessel

As the water in the heating system gets hot it expands; in sealed systems the 'expansion vessel' (a small pressurised container) accommodates the extra volume.

Feed and expansion tank (F&E tank)

Traditional heating system use two tanks that are usually found in the loft. One feeds fresh water to the hot water storage cylinder and the other one (usually smaller) maintains the correct level of water in the heating system. They also allow for expansion of the water in either when it gets hot - hence the name 'feed and expansion' tank.Flow rates

Generally the term 'flow rates' is associated with combi boilers. It refers to how much water (usually measured in litres) can be heated as it flows though the pipes in a given time (usually per minute). A powerful boiler will heat more water therefore providing a better flow rate.

Flue

All boilers have some sort of flue system; there are typically two types:

• Concentric: This system comprises two pipes one inside the other. The internal pipe takes the exhaust gases from the boiler to the atmosphere and the outer pipe supplies air to the boiler. The majority of concentric flues are a maximum of four metres in length and have a wide range of flue bends and extensions. This provides greater flexibility in positioning your boiler.
  
• Twin pipe: This system comprises two pipes. The first pipe takes the exhaust gases from the boiler to the atmosphere and the second pipe supplies air to the boiler. This flue system is useful when the pipes need to be over four metres long. It also has a wide range of flue bends and extensions providing greater flexibility in positioning your boiler. However, this may be less aesthetically pleasing due to the amount of pipe work on show.

Ground source heat pumps

The ground source heat pump system taps into the natural heat found just metres below the Earth's surface.  The heat pump takes the heat at around 10^oC and increases the temperature to a level suitable for a heating system. This stable, consistent energy is then used to provide space heating.