We have a wood burning stove in our house and it provides the only source of heat for the 200 square meter space. It’s a good one, it’s heavy and burns well and it can stay in overnight. We do not, however, have any means of circulating the heat it generates; it simply rises and disperses mainly to the upper floors meaning that the bedrooms up there are generally warmer than the living spaces below, i.e. the wrong way around.
I did temporarily install a fan within the chimney enclosure which enabled me to transfer some of the heat to another room. This is the basis of a popular method of heat transference. It worked well although it was a bit noisy. So when I heard about stove fans (via an earlier post on SFN) I was intrigued.
Stove fans sit on top of your wood burner and are powered by a small thermoelectric generator, this requires no mains power or battery; they are completely autonomous and even vary their speed according to the the heat produced by your stove.
Positioning is important, they must draw cooler air from behind to function correctly. For this reason they must be placed at the rear of the stove. One thing you need to be aware of is that they have an upper temperature limit, there is a bimetallic strip on the underside and if they get too hot this will lift the base up slightly to reduce the temperature of the fan. This failsafe will only protect the device up to a point, if your stove pipe reaches 345 degrees Celsius they should be removed to avoid permanent damage. According to my stove pipe thermometer, 345 degrees is way too hot for efficient operation anyway, so under normal circumstances there is no need to touch it.
So what do they actually do? The principal is simple and could be, though not quite so elegantly, re-created with a desk fan. (Do not put a desk fan on top of your wood burner!) The heat produced by your wood burner will travel directly upward to the top of your room and that hot air will gently descend as it cools or is displaced by more hot air. The further from the burner you are the cooler it will be. The stove fan moves some of that hot air directly from the top of the stove further than it would naturally travel thus creating a more even dispersion of heat.
It works, there is no question about that. How well it will work will be determined by your installation. If you have a ventilation system in place then you may not notice a difference. We do not and as a consequence the result is dramatic. Draughty spots are lessened and there is not so much of a hot spot near the burner.
I have two of these fans, one I purchased and another sent to me for review by Valiant Stoves, a UK based company.
Upon initial inspection they look very similar; they are approximately the same dimensions and of a similar design. The Valiant is the 4 blade model (FIR360) whereas the unbranded model has two blades. Place both on the stove operating at an ideal temperature of 200 degrees Celsius and they begin to spin within a few seconds of each other. The unbranded one always starts first, possibly due to the lighter weight of the blade arrangement. Removal of the fans stops them both after a couple of minutes.
The Valiant is better finished than the ebay purchase, the motor is painted to match the colour of the unit and the handle functions properly, the unbranded one gets stuck easily.
I have tested both for a period of days under similar conditions, they operate similarly, the Valiant is totally silent, the ebay purchase is very nearly silent, I can hear a click every revolution if I put my ear right next to it. I hadn’t noticed until I did that so it’s not noisy by any means. After a few days of use when the stove pipe temperature had reached the upper limit of their recommended use, the unbranded one had a slightly distorted pillar, it had not coped well within the limit of it’s stated capacity and had warped! I was able to bend it back into place but that did nothing to restore my confidence in the cheaper unit. The Valiant had not suffered at all.
In summary, I am impressed with the performance, they both do what they are supposed to but the Valiant does it better, it is made to a higher standard and I expect it will stand the test of time.
If you want a flue thermometer to go with it you can get one here
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