Replace gas boiler with heat pump

Gas Boiler to Heat Pump

Replace your gas boiler with a hydronic air-to-water heat pump for operating savings using your solar power. Also, contribute to reducing greenhouse gas emissions.

Hydrosol has seen a rise of enquiries from people asking if their hydronic gas boiler can be effectively replaced with a heat pump. In short, the answer is yes.

Common questions

  1. Can it be done?
  2. What does it cost?
  3. Will it work with my radiators?
  4. How does the cooling work?
  5. When should I change over my gas boiler?
  6. Do I have enough space for a heat pump?


  1. Yes, it can be done. Hydrosol has been involved in many projects where clients have wanted to replace their gas boiler with an air-to-water hydronic heat pump. For best results, clients have worked on improving the thermal performance of their houses to reduce heat load. This makes the task of the heat pump easier, using less power from your solar panels. For example: Brunswick, Ascot Vale
  2. A hydronic heat pump for an average house will cost around $15k plus installation. A modern condensing gas boiler will cost around $5k plus installation. Allow $2k for other costs such as upgraded power supply and additional labour. You will recover the difference by using your own solar power to run your new heat pump. Also, your heat pump will last longer, be safer and add value to your home
  3. You could replace your gas boiler with a high-temperature heat pump that can heat water to 75 degrees. This would certainly work with your existing radiator panels. However, you probably could, or may already, have reduced your panel heat to less than 60 degrees. If you have been working on improving thermal performance, your heat load will be less and your radiator panels can be set lower (see below). 
  4. The cooling works by running the heat pump in reverse cycle. It cools the hydronic water and absorbs heat inside your house. Cooling works best with fan-coil convectors but underfloor area cooling is also an option. This heat is then transferred outside (see below).
  5. Replace your gas boiler after 10 to 15 years, which is its typical life span. If older than this, it may be operating inefficiently or may even be unsafe and leaking gas. Check your winter gas bills and/or ask your gas boiler service technician. In our experience, a heat pump last up to 30 years.
  6. The best location for your hydronic heat pump is where your gas boiler is currently located. This is because your hydronic flow and return pipes and fittings are located there. Your heat pump can be installed on the ground or raised up if the outlet air needs better airflow. The outlet air should not feed back into the inlet side otherwise this will reduce operating efficiency.


  • Set your boiler to less than 60 degrees and monitor its effectiveness. A lower temperature will be make your heat pump more efficient, be safer with toddlers and less wearing on furnishings. 
  • Try turning down your radiator panels as you work on improving the thermal performance of your house. Every step you take will improve your operating costs.
  • Reduce your night-time temperature settings from day-time.
  • Install thermostatic heads on your radiator panels in rooms so they automatically adjust to your settings.
  • Zone your bedrooms to be cooler than your Living/Dining/Kitchen or home-office areas. Turn off radiator panels in unused rooms.
  • If you can reduce the power demand of your heating and cooling equipment, you will optimize your solar power.

Heat Pump Cooling

A hydronic heat pump can also operate in reverse cycle for summer cooling. Mix and match underfloor circuits, radiator panels and fan-coil convectors with just one hydronic heat pump in heating and cooling modes.

There are two approaches for heat pump cooling:

Hydronic Convector Cooling

Cooling via hydronic fan-coil convectors is the most effective approach for summer cooling. Your heat pump can produce chilled water as low as 7 degrees.

Chilled water can circulate through the coils of your convector. This will produce condensation that is then drained outside to reduce humidity inside.

The process behind this is called latent cooling. It is what happens when there is a change of state from water to gas. Energy in the form of heat is absorbed from inside your home to enable this process. It is the same process that cools us when we sweat.

Consider adding a separate fan-coil convector circuit for effective heating and cooling.

Hydronic Area Cooling

For underfloor heating systems, you get the option of reverse-cycle area cooling if you replace your gas boiler with a hydronic heat pump. It will produce a comfortable floor temperature of around 18 degrees, above the dew point. Whilst this is not as effective as convector cooling, you can make it work. Here are some points to consider:

  • The larger the surface area, the better
  • Reduce your heat load by improving the thermal performance of your house
  • Improve shading to remove sunshine radiation through windows, particularly east and west
  • Install ceiling fans to improve effectiveness
  • Use floor fans if ceiling fans are not an option
Improve thermal performance to effectively change a gas boiler to heat pump
Star Ratings: Guide to Ongoing Power Savings, Tasmanian Government

Thermal Performance Objective

Your thermal performance objective should be to achieve 6 Stars at least. Improving thermal performance is an important consideration if you plan to replace your gas boiler with a hydronic heat pump.

The chart shows the significant reduction in energy use by improving thermal performance. Each higher Star Rating reduces energy use by between 22% and 31%.

Reduce Heat Load

Improve the thermal performance of your house as part of your project to replace your gas boiler with a hydronic heat pump. This doesn’t have to be done all at once, it can be staged. 

Contact us to discuss a prioritised improvement plan.


Heat load benefits include the following:

  • Lower heating and cooling costs
  • Smaller and less expensive heat pump
  • More effective use of your solar power
  • Adds value to your house