Units of measurement

Bar – The unit of measurement of water pressure – one bar is approximately equivalent to a column of water 10m high or 14.5 lbf/in² or 100 kPa (kilopascal).

Flow Rate – L/M – litres per minute is a unit of volumetric flow rate of a liquid.

Head – the pressure of water in a closed system – it represents the difference in the gravitational force exerted by a liquid at two different depths

Kilowatt – KW – a measure of the rate of supply of energy or power, equal to 1000 watts or 3412 BTU per hour

BTU – Abbreviation for “British Thermal Unit”; a measurement of heat equal to the amount of heat necessary to raise one pound of water one-degree Fahrenheit at sea level. (One BTU is equal to about 250 calories.)

Heat loss – Often used as a comparison between manufacturers, the heat loss figures are a measure of the amount of stored heat that escapes from an appliance such as a water heater or hot water cylinder over a period. The heat loss figures are a measure of the kilowatt hours lost over a 24-hour period.

Heating Calculations – These are done to calculate the heat requirements of your room to maintain a comfortable temperature.

Static pressure – The pressure when no water is flowing.

Dynamic pressure – The pressure when the water is flowing.

High Pressure – Fixtures marked as high pressure are suitable for high pressure systems (such as a combination boiler, or unvented system).

Low pressure – Showers marked low pressure are suitable for use on a low-pressure system (such as a gravity-fed system).

Potable Water – In reference to water is that “potable” means it is drinkable water. Water that is suitable for human consumption.

Non-potable Water– unsuitable for drinking

Water hammer – loud banging noise caused by hydraulic shock that occurs when water supply is suddenly shut off, resulting in water moving against the side of containing pipe

Natural gas – a colourless, odourless fuel (primarily consisting of methane) derived from the Earth – odours are added to aid in leak detection

Hard water – natural water containing impurities in various proportions – traditional hardness is a measure of calcium or dissolved solids in a solution, measured in parts per million

Soft water – water that has a low calcium and magnesium content

Condensing Boiler – A boiler that extracts all usable heat from the combustion process, cooling the flue gases – the collected water is then evacuated from the boiler from the condensate pipe.

System boiler – System boilers use a cylinder to store hot water and are like a heat only boiler, but the system is pressurised and has a pump and expansion vessel built into the design.

Heat only boiler – Regular, more traditional boilers, use hot water cylinder as well as a cold water and additional storage tank, usually in the loft space.

Combination boiler – AKA “combi” – a unit which combines both a central heating water heat exchanger and a domestic water heater in one compact, self-contained unit. Unlike a vented heating and hot water system, a combi does not store hot water, rather it heats water as and when required either directly from the cold mains (for the domestic hot water) or within a pressurised ‘sealed’ central heating loop.

Convector Radiator – A radiator that transfers its heat via convection. These will normally have ‘fins’ at the back of the radiator or in between the radiators’ panels.

Panel Radiator – A usually flat surface that is used to transmit radiant heat.

Underfloor Heating – A method of using concealed underfloor pipework to warm a dwelling. It’s a little like turning your entire floor into one big radiator!

Hot water cylinder –There are two types of cylinders – either the open ‘vented’ type or an ‘unvented’ type. Vented cylinders have a vent pipe which subjects them to atmospheric pressure, whereas an unvented water cylinder is plumbed directly from the pressurised mains water supply. Unvented cylinders have many safety features to help prevent excessive pressure build up and hot water expansion.

Expansion Vessel – a tank designed to absorb excess pressure due to thermal expansion

Balance a Radiator – You can ensure that heat is evenly distributed through your heating system by adjusting the lock shield valves on your radiators so that they all run at the same average temperature and each takes the same amount of time to heat up.

Micro Bore System – This is a central heating system with smaller pipework. Standard fittings have 15mm pipework, whereas a Micro Bore System features 10mm pipes.

Surrey flange – A fitting inserted into the top of hot water cylinders which purges the hot water of air before it is drawn off into the outlet. Normally used in the feed for shower pumps.

Rising main – The water pipe that supplies pressurised mains water to taps, tanks, appliances etc. Normally there is a single stop cock which controls the rising main within a property.

Thermostatic radiator valve (TRV) – A Radiator control valves which automatically opens and closes as necessary to achieve the pre-set room air temperature.
Pressure relief valve – A safety device fitted to relieve excessive pressure within a heating boiler or system. Will reset itself once the excess pressure has been relieved.

Power shower – a shower incorporating a device that increases water pressure, thus using more water but creating a more powerful spray.

Boiler Cycling – This happens when a heating system has reached its temperature and the boiler shuts down. A few minutes later the boiler will again fire up in order to top the temperature up as the system loses heat. Once this has been done, the boiler will shut down again. This constant firing and shutting down as the water cools wastes a lot of fuel energy.

Combination valve – a valve used with an unvented cylinder. Includes a pressure reducing valve, pressure relief valve, strainer and check valve.
Pressure reducing valve – controls the pressure of a fluid or gas to a desired value.