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Hydronic Heating

Last Updated May 12, 2021 · Written by Craig Gibson · 3 min read

Hydronic Heating

Hydronic heating is a common form of domestic heating in Europe and the UK in particular (where it is simply called "central heating"). It is ideal for colder climates because it is an energy-efficient way to heat large spaces for extended periods.

However, it is relatively expensive to install, and takes a while to warm up, making it unsuitable for short, quick bursts of heat. For these reasons, it is less common in Australia, with its warmer climate and cheaper energy.

However, as energy prices rise, hydronic heating is becoming a viable and energy-efficient option, especially in areas with colder winters such as Melbourne, Canberra or Tasmania.

Hydronic heating involves a pump circulating hot water from a water heater through copper or plastic pipes to radiators throughout your home. The water is then piped back to the heater to be reheated.

Radiators (which actually provide a mix of radiant and convection heat) are panels fixed to your walls. You can also get heated towel rails for bathrooms and long, thin panels that run along skirting boards. Radiators are generally made of pressed steel or cast iron. Properly serviced, they will last indefinitely.

A variant is in-slab systems, where hot water is piped through coils laid in the concrete slab during construction to provide under floor heating.

Benefits of hydronic heating

Very energy efficient if used correctly.

No smoke or dust circulation.

Flexibility - radiators can be controlled individually to only heat the rooms you want.

Low maintenance.

Factors affecting energy efficiency in a hydronic heating system

1.Water heater: the water heater can run on natural gas, LPG, electricity, a solid fuel such as wood, or using a solar hot water heat pump system. Gas, solar and wood produce fewer emissions than an electric system. The heater should also be insulated to prevent heat loss.

2. Storage or instantaneous heater: water heaters can be either storage systems that keep water continually heated, or instantaneous heating systems that only heat up when the system is turned on. Storage boilers have higher running costs because they keep water hot even when it is not needed, but they respond faster when switched on.

3. Piping: the water cools as it circulates through the pipes, so the shorter the network of pipes and the better insulated they are, the less heat will be lost

4. Thermostats: radiators will generally have individual temperature controls, but a system with an automatic thermostat is usually more energy-efficient system than one controlled manually. Temperatures should be 18-20C for living areas,16C for bedrooms and hallways, and turned off at night. The system should only come on during cooler times of the year and day.

5. In-slab heating is energy-efficient, but is only cost-effective to install during the construction of a new home.

6. Insulating board with reflective foil behind the radiators can reduce heat loss up to 30 per cent on uninsulated walls.

7. Radiators with low water content respond faster and use less energy

Combined heating and hot water

A hydronic heating system can be connected to an existing hot water tank. This has two benefits. Firstly, it reduces installation costs. Secondly, the water flows through the hydronic system, heating your home, on its way to taps and showers, so the system achieves efficiencies by using your hot water to heat your home.

Solar hydronic heating

You can use a heat pump hot water heater system to run a combined heating/hot water system. Heat pumps are regarded as a form of solar hot water, because they use a heat exchanger to extract heat from the air. (Combined heat pump systems use two heat exchange coils - one to heat domestic water and one to heat water for the hydronic heating system.)

Unlike rooftop solar hot water panels, heat pumps don't need direct sunlight and work even in very low temperatures, making them suitable for heating during winter and at night.

A standard domestic heat pump will not generate enough hot water to heat an entire house, but it is sufficient to heat one or two radiators for a few hours a day (which is all you need in warmer regions) and still provide hot water for your home.

In heat an entire home, you would need a second boiler to boost the water temperature when necessary. Such systems - especially with a gas-fired backup boiler - are still very environmentally friendly and energy efficient, with low running costs.

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