Thermal Stores and Wood Burning Stoves – What You Need to Know

Thermal Stores ModelsWood burning stoves are an increasingly popular feature for home-owners and while some opt for a decorative heating appliance, many are looking to use the heat generated to also provide hot water.

Using unvented cylinders is generally not allowed due to the uncontrollable heat generated by the stove.  There are certain stoves on the market capable of linking to a pressurised system but they have multiple levels of safety control which can be very complicated.

The optimum hot water storage solution for wood burning stoves, are therefore thermal stores, thanks to their unique ability to deliver mains pressure hot water, while keeping the rest of the system open vented.

How Does a Thermal Store Work

The thermal store reverses the traditional approach to hot water, where the stored water goes to the taps.  Instead a thermal store is heated, to generally a higher temperature and the store of water can be circulated round the Central Heating circuit.

Additionally - mains pressure secondary water is passed through a high efficiency coil or external plate heat exchanger and draws its heat from the store, before going through a thermostatic mixing valve, blending it to the required tap temperature. 

The stored water is primarily heated by the solid fuel appliance, while a traditional boiler, solar thermal or PV, or an electric immersion can be used for additional heat. Thermal stores are recognised as the most flexible hot water storage solution for incorporating multiple energy sources, including renewables.

How to integrate a Wood Burning Stove with a Thermal StoreThermal Store Wood Burning Stove

To allow gravitational forces to take effect and start the cycle of heat flowing round the system there must be a minimum of 500mm between the centre of the  Feed and Return connections on the wood burning stove and the thermal store Feed and Return. The more height between these connections, the quicker the stored water will heat up.

How Do You Prevent Over Heating Your Thermal Store?

A thermal store will generally sit at around 75-85ºC however when the wood burning stove is used regularly, the heat generated needs to be controlled.  

This is achieved by installing an overheat stat linked to the central heating pump which is activated when the stored water reaches in excess of 85ºC, dissipating the heat through the heating circuit.

A “quench coil” maybe also be advisable where power cuts are likely, allowing cold mains to pass through a small coil in the thermal store which in turn cools it down.

McDonald Engineers UK can also fit a Pressure & Temperature Relief Valve to the store.

Why a Thermal Store

Ideal for solid fuel and multiple heat sources, reduced installation requirements, no unvented discharge rules, very limited servicing requirements., zero legionella risk and drinkable hot water at all hot taps. 

McDonald Engineers UK have the widest range of thermal stores – including their CUBEflow rectangular thermal store CUBEflow unit.  

As well as providing full technical advice on any aspect of hot water storage solutions, McDonald Engineers UK can also customise connection layouts to simplify the installation process.

Click here for more information on our range of thermal stores or call on 01592 611123.