Important terms and conditions


When considering new heating systems or trying to find the solution to your broken or outdated system, it is very likely you will come across some technical terms used to explain the situation. Here is a list of such words that might help you grasp a greater understanding of your system.

Condensing Technology

Changes and developments in technology advances of boiler design has driven boiler constructions to condense to ensure as much heat as possible is converted into useful heat for your home. Water heaters achieve their high efficiency rate by condensing water vapour in the exhaust gases in order to recover its latent heat of vaporisation, which would otherwise be wasted. By condensing this vapour, your boiler will ensure at least a large percentage of money you spend on gas or oil will be converted into heat for your home comfort


Along with vaporisation and the production of heat, when gas or oil is burned within your boiler, condensation is also created. This is evident in the collection of liquid which is then released into the air. However in addition to this condensate being discharged out of the boiler condensate also collects inside the boiler and is drained away either inside or outside your home.


This refers to the transference of heat in a gas or liquid form by the circulation of currents from one region to another.

Convective heat

A process using the natural circulation of air across a heat source and ventilating into a warm space

Energy efficiency

The ratio of the level of services or functions provided to the energy used to provide that output.


The flue is the duct like part of the boiler which allows exhaust gases and waste to exit the boiler. The flue duct is typically located directly behind the boiler radiator to allow waste gases to exit safely and immediately out of the external wall of your home.

Flow Rate

More so relevant in combo boilers, a flow rate is the measurement of how many litres of hot water come out of the tap in a minute. Your boilers flow rate is determined by the amount (and pressure) of water that is provided to your house and the ability of the boiler to heat that water to the intended set temperature. The more powerful a boiler is, the faster the boiler will be able to heat the water coming into your home. The flow rate is purely determined by the amount of water that enters your household per minute, and so flow rate can only increase if the amount of water increases.


Green-star is a rating tool that defines boiler systems as best practice operators within five distinct sustainability categories for its heat production.


An apparatus that converts direct current into alternating current.

Open Vent

This is a term which is also used to describe a Regular boiler type. A Open vent system will include an open vent as well as tanks within the surrounding area. This type of heating system is an outdated construction, typically common in older property’s.

Passive heating

A heating system of features incorporated into a buildings design that uses and maximises the effects of the suns natural heating capability.


Transfer of heat to cooler object or person through contact, as contrasted with that transferred by conduction or convection.

Stack ventilation

The upward movement of air through openings in a building fabric due to thermal buoyancy and/or negative pressure generated by the wind over the roof. Also known as convective air movement

Temperature differential (ΔT)

Heat flow through any building element (e.g. wall, floor, ceiling, window) is directly proportional to the temperature difference on either side of that element. This is called delta T (ΔT) or temperature differential. The greater the temperature differential, the greater the heat flow through the element

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Author: nick thorn