Air vent - A small usually manual valve that requires a key to permit air that has accumulated in the top of the radiator to be released into atmosphere.

Angled Radiator Valves - the flow and return pipework have a 90° opposite turn on them and are for use on radiators where pipe work is coming up from the floor or out of the wall.

Balancing a Radiator system - By adjusting the lock shield valve on each radiator you can make sure that the heat is evenly distributed to all the radiators so they all run at the same temperature and take the same amount of time to heat up.

BOE - Bottom Opposite Ends - Where Radiator flow & return valves are installed on the bottom of the radiator on opposite sides. British Thermal Unit - (BTU or Btu) is a traditional unit of energy which is rarely used, it is watts which is the most used unit of energy today.
1 BTU/hr = 0.29307107 WATTS
EN 442 - The official European Standard for temperature and pressure testing radiators and covers manufacturing standards such as minimum material thickness, paint quality, product labelling, etc.

Pressurized Heating System - A central heating system that is pressurized is a system that once filled with water is then isolated from the cold water supply by a valve on a filling loop , the water is then circulated repeatedly around the system and is not replaced by any new water entering the system unless the filling loop is manually opened.

Combi boiler - a boiler that provides both central heating and hot water.  A combi boiler is a high-efficiency water heater and a central heating boiler combined in the same boiler casing Therefore, no separate hot water cylinder is required.

Convector Heater - usually a radiator, a radiator that is designed to provide heat for a room through mostly convection and partial radiation.

Corrosion Inhibitor - it is good practice to introduce a chemical inhibitor into the water in all central heating systems to prevent internal corrosion of non-inert metals, popular brands that can be used are Fernox and Sentinel.

DELTA T - See tips and advice on the AEL website home page www.aelheating.com

Delta T 50 - The European standard for the testing and recommended operating temperature of central heating systems, which determines the heat outputs achievable from radiators.

Duel Fuel Radiator - A radiator that is connected to the central heating system, but also has an electric element installed for use when the central heating is not required.

Feed and Expansion tank - The water storage tank situated at high level at the top of on open vented system ( opposite of a pressurized system ), which allows the expanding hot water from the cylinder / system to safely expand and be blown out and introduced back into the heating circuit.

Expansion vessel - A small tank used in a pressurized system on either the heating circuit or domestic hot water circuit to absorb excess water pressure (Not the same as an expansion tank)

Central Heating Flow - Is the heated water leaving the boiler and is also the hot water that enters the radiators.

Heat loss calculations (radiator sizing) - These are calculated to provide the heat output requirement of a radiator for a room. The calculations are based on the size and the insulation properties of the room, there is a very simple heat loss calculator that can be used on the home page of www.aelheating.com

Heat output - the amount of heat that is emitted from a radiator or boiler.

Indirect Heating System - is a piped heating circuit that recirculates the same water through a boiler, pipework to heat the radiators and back to the boiler again, the water can be topped up should a leak occur.

Lock shield Valve - A valve that is usually used to restrict the flow of water on the return side of a radiator in order to "balance" the radiator on the system. A lock shield valve will be supplied along with either a "thermostatic valve" or "manual valve"  to be fitted on the flow in.

Manual radiator valve - in principle a Manual Radiator valve operates just like a tap, the head is turned by hand so you can control the flow of water into each radiator and manually regulate how hot the radiator gets regardless of the surrounding room temperature. Manual valves have no labelled settings: you simply turn the valve head until the radiator is giving the correct amount of heat desired for your room.

Mean water temperature (MWT) - a radiator with a flow in temperature of 80 degrees and a return out temperature of 60 degrees has a Mean average temperature across the radiator of 70 degrees. To expand on this ,If you deduct the required room air temperature of 20 degrees from the 70 degrees Mean water temperature you then also have the delta t figure of 50°C (dt).

Open Vented System - uses an expansion tank to introduce water into the system (opposite of a pressurized system)

Radiator- usually contains hot water at an average temperature of 70 degrees that is designed to "radiate" and "convect" heat outwards into a room.

Radiator key - Removing air from a radiator requires a radiator key, but with more modern radiators you can use a flat-blade screwdriver, it is a simple process of turning the key clockwise half a turn until the air stops and water appears. You can buy a radiator key from any hardware or DIY store for a few pounds.

Reducer - a screwed fitting that is designed to reduce the size of the connection on the side of a radiator to suit the diameter of the screwed valve being used.

System Return - This refers to the water going back to the boiler or the exit point for the water on a radiator.

Straight Body Valves - Valves that have a straight body and have a continuous bore from left to right are an alternative to an angle valve that has the flow and return on a 90 degree bend.  . 

Tapping Centre - The center line of the water connection ( where the reducing bush is fitted ) on a radiator.

TBOE - Top Bottom Opposite Ends - Radiator flow valves are installed at the top on one side of the radiator, and the lock shield on the bottom of the other side of the radiator.

TBSE - Top Bottom Same Ends - Radiator flow valves are installed at the top and the lock shield valve is fitted on the bottom on the same end of the radiator.

Thermostatic Radiator Valve (TRV's) - have a built in temperature sensor.  A thermostatic valve automatically will maintain the temperature in a room at the temperature selected on the dial by automatically adjusting the flow of hot water into the radiator.  The automatic control of the valve ensures that the radiators operate as efficiently as possible.

Towel Radiator - A radiator that is designed specifically to warm towels as well as heating a room, often only used in bathrooms or kitchens.

Watts - The Watt is the most common unit of energy used when calculating heating systems, it replaced the BTU, the conversion for

1 WATT = 3.412141633 BTU/hr