Heat powered wood stove fan

How about a wood stove fan? The wood or multi-fuel burning stove is a great way to give a heat source to any room. It is not only practical, but is often a design feature and brings a welcoming feel to most rooms. Everyone who owns a stove knows that a major short coming with a stove is the area in front is the warmest place in the room and the further away you get the cooler the room becomes. Quite often the family pet has the best seat in the house right in front.

Getting an even spread of heat around the room got the engineers working in overdrive to find the best solution and making the stove burner more effective. It was generally agreed that a stove top fan is the best solution, as a fairly small fan has the capacity to move a large quantity of air around a room without cooling the air too much and still creating an even heat throughout. The modern stove fan is built around this premise. By using a fire place fan, the warm air reaches all corners and disperses any heat pockets that gather on the ceiling.

There were obstacles in getting a good source of power to drive the fan though. They found that using batteries not only added cost to the whole exercise, but the stove top could reach temperatures in excess of 570 Fahrenheit, which was beyond the safe usage of most batteries bought in ordinary stores.

Wood stove fan efficiency

Electricity was the obvious answer, but with this solution also came added cost to the wood stove fan. Not only the cost in electricity to power the wood burning stove fan – but also added costs to shield the wires inside from the extreme heat of the stove top.

The final solution was to somehow harness the heat from the wood stove to power the fan itself, and so the heat activated stove fan was born. The heat is transferred into power to drive the stove fan blades by using either the TEG Module and Seebeck effect, or by a miniature Stirling Engine.

Seeback effect in TEG moduleThe TEG Module

TEG is an abbreviation for Thermoelectric Power Generator. The transfer of heat from the heat source or hot body, in this case the stove top, through the electrical conductors to the cold body generates a current and is also known as the Seebeck Effect:

This method generates enough power to run the motor that powers the fan. With no moving parts it’s very reliable, as there are fewer things that can go wrong or will need replacing.

The Stirling Engine

Created in the early 1800s by Robert Stirling to rival the steam powered combustion engines, this small engine was largely ignored by the powerhouses behind the industrial revolution, but used for smaller household devices over the last hundred years.

The Stirling engine uses the heat from the stove top to heat the air inside a cylinder that is sealed with a compressor. The hot air drives a piston up, which turns the flywheel, when the air cools the compressor at the top plunges and completes the turn of the flywheel and resets the piston. The flywheel is attached to the wood stove fan blades and this is how the mechanical energy is created to drive the fan.

The Stirling engine is at a mechanical advantage and is capable of pushing huge quantities of hot air around a room and is used our models such as the Warpfive and is possible to move a staggering 260 cubic feet of air per minute.

Stirling engine animation

The common factor of both of these power sources is they have a low torque motor that stops and starts easily. With models such as the ones from Valiant they have a low temperature starting point of just 113 Fahrenheit, but most will start at around 150 Fahrenheit. You also have to be mindful of the top temperature limits for the heat powered stove fan. We suggest using a thermometer on the stove, the SFR Stove Thermometer quite clearly shows the maximum temperatures for both the TEG Module fans and the Stirling Engine fans. When your stove gets to this temperature you just move the heat powered fan off the stove.

Where to place the fan

The Carfamo Wood Stove Fan placementWhere you place your wood stove fan helps you get the best results. Your fan will usually come with clear suggestions about the best position. Most fans use a Peltier module to guarantee a sufficient heat difference between the cool side and the hot side of the fan, the position of this in the fan means the best place for it on your stove top is to the rear of the stove far away from the flue pipe so cooler air can be drawn in.

Other factors will affect the efficiency of the stove fan like the position of the stove in the room, is it freestanding? Is there much airflow if it’s set inside a fireplace? The rule of thumb is that the fans for wood burning stoves should be placed away from the flue and never directly in front, so set to the right would be best.

As with all these things, everyone’s room is different and we do recommend that you try different positions to find the optimum placement for your i.e., Ecofan. Of course, fan won’t stop working if you can’t put it in exactly the spot shown in the above diagram.

Stirling powered fans, such as the Vulcan or Warpfive, can withstand greater temperatures and don’t rely on a cooling system in the same way, so their placement on your stove top. We suggest you look closely at these fans if you have a large room to heat, or if your stove reaches very high temperatures.

What about gas stoves & inset stoves?

Stoves whose output are generally a lot lower than regular multi-fuel or wood burning stoves can still benefit from the stove fan – look out for SmartFan marked with ‘LT’, Warpfive Glasshoppers or Caframo BelAir  if your stove’s top doesn’t reach 390Fahrenheit.The BelAir low temperature stove fan The stove fan for the inset stove has been brought to the market recently, the Sirocco can be mounted to the door front of inbuilt stoves.

The stove fans have been around now for a while, design tweaks and improvements come in every successive model, which means there is very likely a fan which will suit your particular setup.

Whether you’re looking for something that will improve the heat solutions to the largest of rooms or are looking for something to bring your fuel costs down, many manufactures believe having a fan can reduce your fuel usage by up to 14%. We have taken some of the strain from knowing which is the best one for you by reviewing each wood stove fan model we sell with a reliable and impartial evaluation.