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East Tamaki, Auckland

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Central Heating Explained

Example Central Heating Schematic

Example Central Heating Layout

The heating our living or working environments, by the use of hot water, is not new. The Romans used this excellent system 2,000 years ago. You may recall seeing wall radiators in use in schools or hospitals. Now more and more New Zealanders are centrally heating their homes with this most comfortable and efficient form of heating available. At the same time as providing their domestic hot water for little extra cost. Hydronic Central Heating is pumped hot water throughout your home to either Radiators (attached to a wall) or Underfloor (within a concrete slab).

These methods are briefly explained further on.

Hydronic Central Heating offers:

  • Easily regulated heat
  • Quiet, clean and unobtrusive
  • Lack of dust movement means minimal dust irritation to allergy sufferers.
  • Easy to install – even in existing houses.
  • Compatible with Solar water heating
  • Compatible with pump/mains pressure or low pressure Domestic Hot Water systems
  • No window condensation
  • The ability to use excess hot water to other areas, eg spa pool or hot house.

 The design of a heating system for your home is based primarily upon the heat transfer characteristics of the building structure.  It is necessary to calculate the internal heat load and the heat flow to and from the appliance (heat loss/gain).  This allows for the proper selection and sizing of the appliance to meet the designed heat load.

What can produce sufficient hot water to run a Hydronic System? 

A standard wetback on a free standing woodburner, or an open fireplace can only cope with a Domestic Hot Water Cylinder, therefore a specifically designed boiler is required – fuelled by solid fuel wood. 

Dependent on fuel source and choice of model boiler a system can be manually or thermostatically controlled.  This helps conserve energy, eg when your home is not occupied.

RADIATORS are available in a wide range of styles to suit various needs. They can be easily retrofitted to existing homes where there is under floor space available. They are best located on outer walls of the room, ideally located beneath window sills (where height permits) but can be installed elsewhere to accomodate specific room design or furniture. Radiators are very responsive, coming up to temperature more quickly than underfloor heating. 

UNDERFLOOR HEATING.  Warm water is circulated by a pump via a distribution manifold to individual rooms (known as circuits), using 13mm internal diameter polybutylene pipes embedded in the concrete floor. Ideally the floor screed is insulated with polystyrene to improve the thermal response of the system. Variable spacing of the pipe layout within the floor screed gives the heating engineer freedom to compensate the potential cold zones and to make allowances for thermal conduction of the required floor finish in order to maximise heating conditions. Due to the flexibility of this system a large variation of design can be incorporated including zone controls, radiators, domestic hot water heating and additional heating run off the primary circuits.

 For advice as to the best Central Heating system to suit your requirements we suggest you contact us for a no obligation, comprehensive quotation. Please send us your plans if building new or renovating, or a rough floor plan or your exisitng home

















The following table and guide gives you an idea of how much hot water is used by typical household usage, and how quickly this hot water can be recovered by the heating source (boiler). A typical hot water cylinder powered by electricity only has a 2kw or 3kw electric element.




Recovery Hours from Cold



180 Litres

HWC Size

225 Litres



270 Litres

1 kw/hr

12 hours

15 hours

18 hours

2 kw/hr




3 kw/hr




4 kw/hr




5 kw/hr




8 kw/hr




10 kw/hr




12 kw/hr




14 kw/hr





 Hot Water Usage Guide

Here are some examples of the approximate quantities of hot water that would be drawn from a hot water cylinder set at 65º C.

 *          A five minute shower at 40ºC – low pressure or mains pressure with a flow control valve uses 18-25 litres.

*          A 5 minute shower at 40ºC – set for heavy flow or without a flow control valve fitted uses 75 litres or more.

*          A shallow warm bath uses 32 litres.

*          A full hot bath uses 73 litres.

 Automatic top loading washing machines draw hot water from the cylinder.

*          A hot wash at 60ºC with cold rinses uses 72 litres.

*          A warm wash at 40ºC with cold rinses uses 40 litres.


Many front loading washing machines are connected to the cold water supply only and heat the hot water required.  Some have dual supply and draw hot water requirements from the hot water cylinder.

*          A hot wash at 60ºC with cold rinses uses 14 litres.

*          A warm wash at 40ºC with cold rinses uses 8 litres.

 Many Dishwashers connect to the cold water supply only and do not draw from the hot water cylinder.

*          Dual supply with hot and cold connections for a hot wash and final hot rinse uses approximately 13 litres.

*          A single connection to the hot water supply for a 65ºC wash and rinses uses 24 litres.

 Hand Washing

*          A small sink of hot water at 55ºC uses 12 litres.

*          A large sink of water at 55ºC uses 17 litres.