Hydronic heating

Hot water is one of the most effective form of home heating.

13apr hydronic heating hero2

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.

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.


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.


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.


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.


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

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.


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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Member comments

Get access to comment

Geoffrey M.
14 Mar 2019
Polarenergi NZ

I recently saw this technology at a home show and it seemed very interesting. We are building a new house so the very low running costs were of interest.

The benefits they claim are the following. Any feedback would be most welcome.

Some key differences and benefits of Polar Energi over and above other systems...

The unique design in the transfer of energy in the refrigerant gas to the DHW and waterborne floor heating system is what makes Polar Energi more effective in operation and a world-leading product.

• No circulation pumps for domestic hot water.

• No 3-way valves for domestic hot water.

• No electric input for the domestic hot water.

• No additional energy losses through a secondary heat exchanger for domestic hot water.

• Low storage volume – quick recovery it equals more efficiencies with 400L plus of hot water in the first hour. (This is equivalent to a 300L system).

• No buffer tanks required for fluctuating flow rates on the central heating system.

Its efficiencies come from a unique, future thinking design of the Polar Energi cylinder.

Key Benefits - Superior warranties

• Panasonic Inverter Heat Pump – 5 years warranty

• Polar Energi Cylinder – Stainless Steel, electric anode – 10 years warranty

• PV compatible with its intelligent RTC5 controller (standard)

• Great for new homes and existing systems upgrades

• It’s 35% more efficient than any other heat pump and equates in an actual saving in running costs of 100%

• Polar Energi has options to suit your personal requirements.

Lynda M.
22 Feb 2019
Diesel boilers

Have you any comments re diesel boilers for radiators? We live out of town in a villa so no piped gas and gather bottled gas is a costly system. thanks

Consumer staff
27 Feb 2019
Re: Diesel boilers

Hi Lynda,

We don’t currently have any information on diesel boilers, but you might find our article on home heating useful when comparing running costs: https://www.consumer.org.nz/topics/home-energy-costs

Kind regards,
Natalie - Consumer NZ staff

David M.
27 Jun 2018
Can suck a lot of energy

We built & installed our own underfloor and radiator hydronic heating from standard components. Some lessons after the fact
* Pipes have to be securely tied to mesh, surge of concrete pour can dislodge them from sticky brackets
* Pipes closer to the surface obviously heat better and lose less heat to ground
* The special under concrete plastic compression pipes aren't sun tollerant. You can't leave the exposed tails out in the sun during the construction process, they go brittle & crack.
* Edge insulation of the slab is essential, often missed in older documentation or underfloor install guides
* Can suck a lot of energy. We use solar hot water, it would be uneconomic with direct electricity.
* Our European made steel with chrome over radiator has rusted in NZ conditions.

Previous member
15 Aug 2015
Review of Different Suppliers

Is there any review available of the different suppliers of hydronic heating systems? Also, is there a review of air-water heat pumps? I can only see the review of air-air heat pumps?

Previous member
17 Aug 2015
re: Review of Different Suppliers

Hi Mark,

Thanks for your inquiry. We don’t currently review hydronic heating systems or air-water heat pumps. EECA have some good information on heat pump water heating on their website: http://www.energywise.govt.nz/products-and-appliances/water-heating/heat-pump

You may also be interested in this 2009 pilot report comparing the energy and economic performance of a range of residential heat pump water heating technologies: http://www.eeca.govt.nz/sites/all/files/hpwh-pilot-report-final-15042011.pdf

George - Consumer NZ staff.