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Hydronic heating

Hydronic heating’s the technical name for water-based heating – a well proven and effective method of warming the whole of your house. It’s very common in Europe but less so here because it's more expensive to install than our more common heating systems. We take a look at what to consider.

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Central heating

The heat from a traditional heater, woodburner, gas fireplace, electric heater or heat pump is released directly into the room where the appliance is installed. In open-plan houses this heat can spread somewhat throughout the open area. That's unlikely in houses with separate rooms: the heat source can overheat the room where it's installed and the rest of the house remain cold.

Historically our houses have been poorly insulated. Poor insulation means high heating costs from avoidable heat loss. This is changing because modern houses – and older ones that have been insulated and double glazed – leak much less heat. Less heat loss means lower running costs, opening the way for even whole-of-house (central) heating.

Enter: hydronic heating

Hydronic heating is suited to uniformly heating the whole house, including multi-storey dwellings. It can often also be used to heat the household’s hot water.

Hydronic heating works by separating the place where the heat is generated from where it's released. To do this it needs a way of moving heat from one place to another as quietly as possible. The answer is hot water in insulated pipes.

It takes a lot of heat to raise the temperature of water – and so hot water carries a great deal of heat energy. With insulated pipes moving the hot water around, a substantial amount of heat can be spread relatively easily from a single source to other places throughout the house.

Components

A hydronic heating system has 3 major components:

  • a heat source that's located in a convenient place (away from where the heat’s required)
  • a hot-water distribution system that transfers and distributes the heat
  • a means of releasing the heat where it's required.

A control system monitors and controls the overall system.

Heating

The heat source is commonly called a boiler – although the water isn't heated to boiling point. Different models burn gas, diesel, logs or wood pellets. Others use a heat pump to heat the water (see below). You need to check with at least two heating companies to determine which type is best for your locality.

Heat pumps
Most domestic heat pumps extract heat from the air outside your house and use it to directly heat the indoor air. The heat pumps mentioned in this article are slightly different: they extract heat either from the outside air or from the ground outside the house and use this to heat water – which is then piped throughout the house.

Distribution

Once the water is heated it needs to be distributed to where the heat’s required. This is done through a system of insulated pipes and any associated control valves and pumps: the pipes are run from the boiler to an underfloor slab or to individual radiators. The house can be divided into several heating zones that can be heated at different times, to different temperatures.

Releasing

There are two main systems for releasing the heat into the house: underfloor heating and radiators.

Underfloor heating. (Image: Central Heating New Zealand Ltd.)
Underfloor heating. (Image: Central Heating New Zealand Ltd.)

Sometimes underfloor heating can be retrofitted under timber floors or over existing concrete floors. But it's mostly formed by a buried grid of pipes laid before an insulated concrete floor slab is poured. The hot water’s circulated through the pipe grid and this warms the concrete floor.

Radiators are often mounted close to a wall with a gap behind them to allow air to circulate. The radiators can be placed throughout the house and sized to suit each room. Various sizes and shapes are available. Most radiators have a control valve so the temperature of each room can be individually controlled.

Radiator heating can be retrofitted because the connecting pipes can be run under timber floors, inside walls and over ceilings.

Costs

Installation costs vary from $13,000 to more than $40,000 (it depends on your house and which system you choose). Running costs can vary from around 6 cents per kWh to over 20 cents – again depending on the house and system.

Heat-pump systems usually have the lowest running costs. However, if your house has reticulated gas, then a gas system may be the most cost-effective combination of installation and running costs.

Our view

  • Hydronic heating is a well-proven method of central heating for suitably insulated houses of all sizes.
  • All the system components need to be specified correctly for the system to deliver the desired level of warmth throughout your home.
  • Use an experienced heating company to specify the system’s components and oversee the commissioning and installation.
  • Make sure you get more than one quote.

Report by Bill Whitley.

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