How Does A Wood Stove Fan Work?

If you have a wood burning stove you may have seen, or even own, one of these seemingly magical stove fans that sit on top of the stove, spinning, with no evident source of power. Well I hate to burst your bubble but it isn’t magic at all its some clever science!

A wood stove fan works by utilizing the heat from a wood burning stove to generate power. There are two types of stove fan, each thermal powered fan uses temperature differential to generate power in a different way. One type of stove fan works by converting heat into electricity and the other type of fan works mechanically, moving pistons, which in turn rotate the fan.

The two types of stove fan mentioned above are Sterling fans and Thermoelectric Generators (TEG). Each of these fans works in a different way to circulate warm air from a wood burning stove around the room or into another room, depending on where it is pointed.

How Does A Thermoelectric Generator Fan Work?

A thermoelectric fan is essentially a “heat sink”. The heat from the stove is drawn up from the base of the fan to the fins at the top. This movement of heat generates an electrical charge, via two semiconductors, which powers a small motor that rotates the fan moving the warm air away from the fins.

If you look at a thermoelectric fan you may notice sandwiched in-between the base and the fins there is a white plate. This is in fact two semiconductors. One semiconductor is positively charged and the other is negatively charged.

The heat drawn up from the base of the stove fan passes through the semiconductors, causing electrons from the negatively charged side to pass to the positively charged side. This movement of electrons is electricity and is known as the Seebeck effect.

The electricity generated powers a small DC motor that rotates the stove fan blades, cooling the fins, drawing more heat up from the base and so the cycle continues.

How Does A Stirling Engine Fan Work?

A Stirling engine fan for a wood stove works by converting a difference in temperature into mechanical work. The base of the fan contains a cylinder that is warmed by the stove, the air within the cylinder warms and expands moving a piston upwards. The cool top plate cools the air causing it to contract, this pulls the other piston down. This piston movement rotates a drive shaft turning the fan.

The warming and cooling causing the piston movement is called cyclic compression and happens many times per second, producing the energy needed for the Sterling engine fan blades to rotate. 

Stirling engines are mechanical and contain no electronic components, therefore they only need a difference in temperature between the top and bottom plates to work.

Stirling engine fans run very quietly which makes them a great choice of fan to use in your living space, they also look great and it is fun to watch them operate.

At What Temperature Do Stove Fans Work?

As both, thermoelectric stove fans and Stirling engine stove fans work in different ways they also operate in different temperature ranges.

Thermoelectric stove fans generally operate in a temperature range between 122°F(50°C) and 662°F(350°C).

Stirling engine stove fans generally operate in a temperature range between 194°F(90°C) and 845°F(450°C).

These temperatures can vary from manufacturer to manufacturer so it is best to check the specifications on any fan you have bought or are considering to buy.

As you can see thermoelectric fans tend to have a lower minimum start up temperature, the temperature at which the blades of the fan begin to turn, of around 122°F(50°C) compared to Stirling engine fans which have higher start up temperatures of around 194°F(90°C).

Once the fans have started to turn on each of the fans, the speed the fans rotate at will increase as the temperature of the stove rises until they reach their maximum rotational limit.

In addition Stirling engine fans can operate at higher upper temperature of up to 845°F(450°C) compared to 662°F(350°C) for the thermoelectric fans.

Thermoelectric fans can overheat above 662°F(350°C) causing damage to the components. Most fans now have an overheating protection strip on the base. This is a strip of thermo-reactive metal that deforms, causing the base of the fan to lift slightly, when the temperature of the fan is too high.

When the heat protection strip has been activated and the fan base has lifted slightly the fan will usually become noisy while spinning. If this occurs carefully remove the fan and place it somewhere suitable to cool for a few minutes.

You may need to take these temperature considerations into account if you are thinking about buying a stove fan.

How Much Air Does A Stove Fan Move?

The air moved, airflow rate, by a wood burning stove fan is measured in Cubic Feet Per minute (CFM) or Cubic Meters Per Minute, (CMM) in metric.

There is a huge variance in the airflow produced by stove fans because there are many different sizes and designs. Typically Stirling engine fans are more powerful than thermoelectric fans and have a higher airflow rate.

Thermoelectric stove fans can range in maximum airflow speed from 100 CFM (2.83 CMM) to 350 CFM (9.91 CMM).

Stirling engine Stove fans can range in maximum airflow speed from 200 CFM (5.66 CMM) to 442 CFM (12.51 CMM).

The Airflow produced by the fan is something easily overlooked but should definitely be taken into consideration before buying a stove fan. If a stove fan can move more warn air, it will help spread the heat from your stove faster and further.

Where To Place A Wood Stove Fan

The position of a stove fan is an important factor in getting the most out of it. .A stove fan needs to be placed on a flat, level surface to operate correctly, and must be placed away from the flue pipe.

It may seem strange that the fan needs to be kept away from the flue because we want to spread the most heat around the room, but placing the stove fan too close to the flue may cause the fan to become too hot.

The best position for a stove fan is on the back edge of the stove where it can draw cooler air from behind the stove to be mixed with the warm air rising from the top of the stove to then be blown in whichever direction you choose to aim the fan.

As you can see in the picture of my wood burning stove below, I have two thermoelectric stove fans on top of my stove placed away from the flue, on the back edge and pointing in opposite directions to help circulate more warm air.

Thermoelectric Stove Fan VS Stirling Stove Fan

Now that we know how each type of stove fan works lets take a look at the pros and cons of each of them.

Thermoelectric Stove Fan

Stirling Stove Fan

I use thermoelectric stove fans in my home, although I would very much like a Stirling stove fan. I love to watch them running, the extra airflow is an advantage and they have a longer lifespan than thermoelectric fans which can stop working when components fail. At the time of writing this, cost has been the deciding factor in my choice of fan. I have been able to buy two fans for much less than half the cost of a Stirling fan.