Central heating systems
Central heating simply fills the overall area – the whole house - with warm air. It does this by slowly drawing all the air out of the overall area through a centrally located return air duct and passing it through a heater before returning it to the overall area via a network of smaller ducts.
This warm air is then reintroduced through floor or ceiling outlets at the outer edges of the house. From there it slowly makes its way back to the return air duct to start the cycle over again.
A central heating system offers many benefits and should add value to the building.
Warm zones and times
Central heating responds quickly to climactic changes and can be programmed to come on and off at a desired temperature level. This ensures the home will be at a comfortable temperature when, for example, owners return home or wake in the morning. Additionally, central heating systems can be zoned so that the home can be heated in different areas as desired. For example, living areas can be heated during the day and the sleeping areas at night.
Health benefits
Central heating provides long term health and maintenance benefits because the warm air being circulated results in a drier house, eliminating mould and mildew problems. During the warmer months the system may be used for ventilation purposes, which also assists in the prevention of mould and mildew. Over time this will reduce household maintenance costs.
The drier environment also reduces the incidence of dust mites in the building.
Central heating units
Central heating units for internal or external installation are available in a range of sizes. Depending on the unit chosen, with output varying from 13.5 – 35kW, dimensions may be approximately:
- smaller models 457 x 395 x 1122mm (LxWxH)
- larger models 1320 x 565 x 1160mm (LxWxH)
The unit is connected to a series of outlets, or ducts, which are positioned strategically throughout the home. By drawing air through a return air grille and heater, the unit then returns warmed air through the outlets for whole-home heating.
The heating unit itself can be installed under the floor, in roof space, or on the exterior of the building. If installing the unit under the floor or in the roof area, it will need to be flued to the outside. See Ventilation and flueing for the required clearances. The system should be located to minimise noise transmission to the heated area.
Installation - external units
External units should be located to ensure that operation of the unit - fan noise, flue emissions - and aesthetic considerations are acceptable to the home owner or neighbours.
The flue terminal is located on the appliance itself so the appliance must be located in accordance with NZS5261:2003, Table 16. Refer to Ventilation and flueing for more details.
Installation - internal units
Consideration should be given to the noise the unit will make whilst operating, and should not be located directly over sleeping areas.
Central heating units most commonly have fan assisted flues and the flue terminal must exit the building in accordance with NZS5261:2003, Table 16.
Central heating with floor outlets
The introduction of heat at floor level will achieve a good heating effect because the heat enters and mixes at a low level, where the air is at its coldest, and then rises to heat the room. The floor inlet position should be carefully selected to give the best heating effect.
Positioning of floor outlets
Whenever practical, the outlets should be placed below any window to offset the cold transmitted through the glass, to reverse cold air currents and to reduce condensation on the window.
The outlet will normally be placed 100mm from the wall. However, when placing below windows, a greater distance should be allowed so that the warm air will not billow behind the curtains, impeding the heat circulation.
As a general guide, each heating outlet will heat around 15 square metres (at a stud height of 2.4m).
The floor vents are available in a range of colours and are approximately 350mm x 150mm making them very unobtrusive.
Central heating with ceiling outlets
With the correct airflow, ceiling outlets are approximately three percent more effective than floor grills.
For maximum efficiency, ceiling diffusers should be carefully located to counteract cold transmitted through windows and the draw of air returning to the return air grill. Unlike floor outlet systems, ceiling outlets require a higher velocity to direct the warm air down to floor level in order to create the right mixing effect.
Installation
The return air intake for ceiling outlet installations must be positioned as low as possible to avoid short cycling and to allow the draw-off of the coolest air from the floor level. This can generally be accomplished by using a bedroom wardrobe, linen or broom cupboard, or even boxing in a duct on an internal corner down to floor level.
Ceiling outlet installations with a height of 3.2m or more need special consideration.
The ceiling vents are round with diameters of either 250mm or 300mm and available in white.
Return air grills
The return air creates an undetectable vacuum which draws air from throughout the home. This air passes over the central heating unit heat exchanger, gaining additional temperature before being redistributed throughout the system outlets.
Return air grills installation
The return air grills should be placed in a reasonably central location that is both aesthetically pleasing and has an unrestricted airflow from as many outlets as possible. The most common location is either an entrance way or hallway, with the grill being fitted to an inside wall and the ducting brought through a cupboard. When this is not possible, a heavy grade floor grill can be fitted.
Grills must be at a low level due to thermal air characteristics, and kept away from supply outlets and anywhere where strong smells may be introduced and circulated throughout the building.
