How to Choose the Right Hydronic Heating Boiler or Heat Pump for your System

Gas Boilers have been the traditional go-to option for Hydronic Heating Systems and still will be for many years to come, however, Heat Pump technology has come along in leaps and bounds as Europe drives towards more efficient and renewable appliances in their response to changes in our climate. Gas Boilers easily heat most projects while Heat Pumps won’t suit all projects. So how do you choose a hydronic boiler or heat pump for your system?

In this article, we aim to cover topics so that you can make a much more informed decision including;

  • How much heat energy does your home require to heat?
  • What energy options are there and how efficient are they?
  • Is a Heat Pump or Gas Boiler more suited to your Project?
  • How to the upfront and running costs compare?
  • Should you Include Domestic Hot Water or Not?
  • What Brand should you choose?
  • What other considerations are there?
Keep Calm Choosing a Boiler for Hydronic Heating is all about the kW

How much heat energy does your home require to heat?

Knowing how much heat energy your home requires to heat to a comfortable temperature is very important in choosing your hydronic boiler. It is also the first step in understanding if a heat pump is going to be suitable for your project.

In the heating industry kilowatts (kW’s) is the unit of measure used to denote the amount of heat energy that a home requires to heat to a comfortable level in winter. At dPP Hydronics we use a range of calculation methods depending on the type of hydronic heating (Slab or Radiators), and type of boiler (Gas or Heat Pump)

Gas with Panels

We calculate that 0.14kWs per square meter will heat a room easily and quickly. It’s a high number, but it guarantees a home will heat up correctly and quickly.

Gas with Slab Heating

For Slab heating, we use a far smaller number, as it is a heat that slowly builds up and then maintains a temperature in the slab that creates a comfortable home at high efficiency. To ensure a boiler is the correct size we allocate 1.5kWs per circuit of heating, which covers around 20 sqm.

Heat Pumps

Because Heat Pumps are very expensive as they go up in size, it is best to use a homes energy report to ensure we can use the smallest (most affordable) heat pump. An energy report will tell us exactly how much energy that build will need to heat in the coldest days of its location. This way we can safely choose the smallest one, instead of over calculating the way we do for a gas boiler as they are much cheaper and much larger in terms of heat output.

If you are considering radiator panels you can use our calculator to give you an idea of what size panels you may need.

Different kWs from other Suppliers

It’s important to note that due to many components in the construction of a home, different people can easily calculate a different kW rating. A slightly different rating will have a negligible effect on the most important result: the comfort of your home.

If you would like to know the kW’s that your home requires feel free to send through your floor plans – we can calculate this within a day and give you a price at the same time. You can then use that info to continue your research if you wish.

What energy options are there and how efficient are they?

Knowing what energy options you have to power your hydronic heating system along with their pros and cons is another large step in making a decision in choosing your hydronic heating boiler or heat pump.

While Gas fired boilers are the most common and affordable heating system to install, Heat Pumps are becoming more and more popular due to their very low running costs and renewable credentials, especially when solar panels and batteries are also being installed.

However, their upfront costs are much larger than boilers and they produce far less kWs and so don’t suit all projects.

Hydronic Boiler Cost Comparison Graph

Natural Gas

The most common form of energy used in Australia for Hydronic heating systems in Natural Gas. This is due to both the access we have to natural gas in most metro areas, and due to the kW outputs being most suitable to our usually very large homes when compared to European ones.

In Australia, we offer both a standard and a high-efficiency boiler that is around 15% cheaper to run. Standard boilers are cheaper upfront, however, we highly recommend upgrading to a high-efficiency condensing boiler due to the running costs being much lower. In 1985 Bosch invented the condensing boiler that is around 99% efficient by preheating the water entering the boiler with what would otherwise be the ‘leftover’ hot exhaust gas.

Bottled Gas – LPG

Most new clients are very wary of LPG fired systems during their investigation period, but they need not be. Due to the exceptional efficiency of a condensing boiler, LPG fired hydronic systems are surprisingly affordable to run. Condensing boilers are around 99% efficient and most clients with them report they go through far less than they would expect. Around 6 – 12 bottles a year depending on the size of the home.

While LPG can seem like hard work, most areas that don’t have town gas have a great local supplier – and LPG is still going to be the best solution in terms of both install and running costs. At last check, they were around $150 a bottle delivered. You should have one connected and one spare full cylinder. When you empty one you can order a replacement so that you know you aren’t going to run out in winter.

Electric Hydronic Heating Boiler

Electric Boiler

When you don’t have any form of gas and a smaller home an electric boiler is an option. Running costs are high but can be offset by solar panels. Installation costs are similar to a gas boiler for a standard-sized system. A mid to large-sized system will probably require 3 phase power and will increase the install cost by a couple of grand.

A pure electric boiler is rarely installed as they only suit very small apartments that are often built where natural gas is available. The running costs of a pure electric boiler are far higher than a gas-fired boiler.

Hydronic Heat Pump

Heat Pumps are a renewable technology as they take energy from the air and convert it into heat energy in water at around 300 – 500% efficiency depending on the quality of the heat pump. It almost sounds like magic to be able to absorb 1kW of air energy into 3-5kWs of heat energy in water, and the fact is it’s not, but, the technology to do this is very expensive and has its limitations.

Heat Pumps are still considered new technology and are easily misunderstood by clients and installers alike. dPP Hydronics has invested significant resources into staff training and having installed numerous heat pumps on a variety of installation types now consider ourselves experts in heat pump installation. It is our aim to become leaders in the industry and this is why our key heat pump partnership is with Stiebel Eltron, the global leaders in heat pump technology.
If you are considering a heat pump you will want to read our article ANSWERED: Is a heat pump suitable for your hydronic system?


Geothermal is a Heat Pump hydronic system that draws on the constant temperature of the earth to boost water temperatures to around 50ºC which is perfect for in-slab heating. Circuits of pipe are installed under the earth where a constant 18°C is present no matter what time of year it is. The running costs are incredibly efficient, however, the installation costs are high due to the cost of the heat pump and the extent of the earthworks.

We recommend contacting Stiebel Eltron for further exploration. dPP Hydronics don’t currently install geothermal in earth circuits but can install the in-slab pipework, manifold and mains pipework to the heat pump.

Timber & Pellet Fires

A great option when you have access to large amounts of firewood and the time to manage the fire. Adding a fire powered heating unit to a hydronic heating system will add quite a few thousand dollars to your system. Most commonly they are installed on working land such as farms, up in the mountains where there are limited services or in enthusiasts homes.

To get heat from a hydronic system, you must first have built a fire to raise the water temperature enough so that the hydronic system functions. They can be backed up by a booster, but then you’ve simply invested a lot in ‘adding’ a fire to a functioning hydronic system. If you are not trying to get off the grid and have access to gas or power then we would recommend installing a standard fireplace that will complement the hydronic heating and being independent has its advantages.

What Brand should you Choose?

As with all purchasing decisions, you should consider your budget, quality of the product, expected service and intend in the purchase.

At dPP Hydronics we have partnered with Bosch Hydronics and Steibel Eltron Heat Pumps. They are the highest quality hydronic appliances, and German brands synonymous with quality, durability and technology.

Having installed hundreds of boilers from such brands as Sime, Immergas, Bosch and Baxi we can confidently say that Bosch boilers are the best. Not only are they the most efficient, but they are truly the leaders in the manufacturer of gas boilers having invented both the Combi Boiler in 1968 and the Condensing Boiler in 1985.

How to Choose a Hydronic Heating Boiler Presentation

Other Considerations with Hydronic Heating

Combi Boilers – Instant Domestic Hot Water

A Combi boiler is a boiler that can provide domestic hot water as well as water for hydronic heating. These are a great option for a small home or single bathroom, however, there are important limitations to be aware of.

A Combi boiler has a low flow rate so when they are used as an instant domestic hot water system they are only suitable for a single hot tap being on at one time. They also need to be installed as close as possible to the hot water location so the hot water reaches the outlet quickly.

Combi Boilers – Boosted Storage Domestic Hot Water

An all in one unit that provides a boiler for the hydronic heating and domestic hot water with a storage unit. Having a storage unit means that you can provide all domestic hot water with your hydronic heating boiler. This unit can provide a home with up to 3 bathrooms with its total hot water requirements, and means you don’t require a separate domestic hot water system.

Solar Heated Water

Hydronic heating is a closed circuit so solar hot water can’t be used in a hydronic heating system. However, it can be used for domestic hot water with a combi boiler as a boosted storage system.

Solar Power

Solar power can be used to offset the power costs of an electric fired system. Hydronic heating requires a large amount of kW’s so realistically you would never be able to generate enough kW’s from solar in winter to completely cover your energy costs.

If you have any questions please write them in the comments section below.