Connect a Wood Stove to a Solar Water Heater
For a wood stove with wetback or water jacket, or using the flue
- Solar hot water and wood heaters make the perfect combination.
- With a correctly sized solar hot water system, the sun will provide at least 70% of a household’s hot water needs.
- However, in the colder months, solar hot water systems may need boosting, and this is when households with wood heaters can use them to keep the house warm.
- So why not use some of that heat going up the flue to heat the water?
- It makes good sense to use wood heaters or stoves fitted with water jackets, otherwise known as ‘wet-backs’, to provide hot water boosting.
Electric and gas boosters have thermostats to switch them off when the hot water systems storage tank reaches a predetermined temperature, normally 65°C, but wood heaters, on the other hand, are an ‘uncontrolled heat source’. This means that the input of heat from the firebox to the hot water storage tank cannot be easily and quickly switched on or off; wetbacks will just keep on adding heat whilst the fire is going. We recommend that you never cut off the water flow to the wetback, as this can cause a potentially explosive build-up of steam, and running the fire with an empty wetback can cause it to burn out very quickly, reducing its lifespan.
There are two options for dealing with this safely. Both options require the hot water storage tank to be located above the wood heater and sufficiently high so as to ensure the wetback always has water in it. The systems thermosyphon heat transfer must not be impeded by any constrictions. As the water heats up, it is critical that the flow of hot water up to the storage tank and the return of cooler water back down to the wetback is not impeded.
Connecting a wood stove to a low-pressure hot water storage tank
Some solar hot water systems have the storage tanks ‘open vented’ so that the main body of stored hot water is not under mains pressure. These systems may rely on gravity feed to supply the hot water to the house, or they have their own heat exchanger coil inside the tank, that supplies the house at mains pressure.
Wetbacks can be safely connected directly to the low-pressure open vented part of these tanks, so with these systems, no separate heat exchanger is required.
Connecting a stove wet-back to a mains pressure hot water storage tank
Using wood stoves to heat mains pressure solar hot water systems works best with the traditional roof-mounted ‘close-coupled’ solar tanks because the solar tank is aleady located above the level of the wood heater, and no pump will be required.
Most solar hot water storage tanks are at mains pressure and therefore need to use a heat exchanger, which must be installed below the level of the solar hot water tank.
In principle, this is a simple device with one pipe inside another, larger pipe. The outside pipe usually has the water from the wetback flowing through it and is ‘open vented’ at low pressure, whilst the inner pipe transfers heat from the outer pipe into the solar storage tank at mains pressure. The outer pipe has an extension rising up to a small open vented make-up or header tank situated just above the centreline of the main storage tank. Any water lost due to boiling is replenished from this header tank. Heat-exchangers and their header tanks are available through Solazone. Many solar roof tanks in Australia’s cooler states have glycol (a frost-resistant heat transfer fluid) going through the solar collector panels and a separate heat exchanger within the solar tank. In these types of systems, it is this fluid, glycol, that the water from the wetback heats in the heat exchanger suspended inside the roof space below the solar unit.
Using a wood fire on a winter’s day to keep warm, while at the same time boosting the solar hot water system, allows households with this set-up to enjoy free hot water all year round. Well-maintained wood fires burn so efficiently that they produce relatively small quantities of greenhouse gases, using the renewable resource of wood. In fact, they emit less than 20% of the greenhouse gases emitted from open fireplaces! Wood is not a fossil fuel and can be harvested from timber planted for wood and firewood.
These pictures show an Edwards LX solar hot water unit connected to a wood stove, using an encased 2-metre heat exchanger. Mains pressure can be maintained for the hot water service, whilst the stove circuit is open vented for safety.
Connecting an LX model Edwards Solar is easy using a heat exchanger. The glycol circuit of the Edwards unit is connected to the heat exchanger, and the stove side of the heat exchanger is maintained at low pressure using the supplied stainless steel top-up tank. The glycol circuit of the Edwards LX must never be connected directly into the woodstove. This would void the warranty and cause a potentially very dangerous situation.
How to install the 2m heat exchanger to a roof-mounted tank
- The heat exchanger is installed immediately below the solar hot water tank, either inside or outside of the roof, with a definite slope on it to assist in heat transfer.
- The stove water pipes must be installed with a continuous slope downwards towards the stove, with no flat or up-hill sections to cause heat locks.
- In general, the slope must at least 1 in 10, and the pipe diameter at least 20 mm or 3/4″ copper.
- The hot pipe should be well-insulated all the way up, as should the entire heat exchanger.
Other types of Heat Exchangers are also available to suit unusual situations. Feel free to ask what would be best suited to your particular application.
Thermosyphon Kit
To connect up your mains pressure solar water heater with tank located on the roof, to your wood stove located below.
It includes:
-
- Two-metre long Tedson heat exchanger
- 12-litre top-up tank with float valve for the stove circuit
- Splash tray for the top-up tank, if it is to be installed inside the ceiling space.
- Installation instructions and plumbing diagram.
Tedson bare copper heat exchanger (uninsulated)
Connecting a Tedson Heat Exchanger
For Ground-mounted pumped systems, this is how it works
- The pressure in ground-mounted tanks is usually higher than what you can put through a wood stove, so a heat exchanger may be required for the different pressure fluids.
- You will also need an overflow and top-up tank for the stove circuit to allow for the chance of boiling
The ground-mounted tank high-pressure installation kit:conprises:
- Solar Mio Compact heat exchanger – 830mm long x 110mm square.
- 12 litre Header and top-up tank, with safety tray
- Pump and controller
Solar Mio compact heat exchanger – all connections are 3/4″ BSP
The Solar Mio heat exchanger is for pumped systems connected to ground-mounted tanks, or where the height difference between tank and wood stove is insufficient for thermosyphon to work.
Heat Exchanger Plumbing Diagram
This is how you connect your wood stove to the heat exchanger and hot water storage tank
Download Heat Exchanger Plumbing Instructions Diagram here
Overflow, expansion and automatic top-up tanks
 Various sized copper and stainless steel top-up tanks with ball valve |
Various sized copper and stainless steel top-up tanks are available, with ball valve for automatic filling.
Stove Flue Heat Exchangers – use when the wood stove has no water jacket
The Stainless steel stove flue heat exchanger fits to the base of any standard 6 or 8 inch stove flue base, to capture some of the waste heat going up the flue, and to use it to heat water.
Very simple installation, and always available.
Heat Exchanger Kits & Accessories Prices – February 2026
| Thermosypon Kit – Tedson HE, 12l Top up tank, splash tray and instructions | $1300 |
| Ground-mounted tank kit – Solar Mio HE, Top up tank, circulation pump & controller | $1990 |
| Separate items | |
| Tedson 2m copper heat exchanger for in-roof connections | $895 |
| Solar Mio 830mm compact high performance heat exchanger (only for pumped systems) | $899 |
| Header Tank 4-litre copper expansion tank & ball valve | $295 |
| Header Tank 12-litre copper expansion tank with ball valve, check valve & tray | $450 |
| Header Tank 22-litre copper expansion tank with ball valve, check valve & tray | $495 |
| 3-litre Insol Stainless steel top up tank & ball valve | $475 |
| Stainless steel stove flue heat exchanger for 150mm Flue | $795 |
| Stainless steel stove flue heat exchanger for 200mm Flue | $825 |
Delivery cost from the factory is extra.