Calculate the efficiency of your wood stove

The efficiency of a wood stove is a very useful indicator of how much fuel is used and how much is 'wasted'. We see figures close to 80% for the modern stove. Although they give an indication of the effectiveness of the latter.

How do they calculate the efficiency of a wood stove?

First of all, it is essential not to confuse the heat production figure, expressed in kilowatts, with the efficiency coefficient indicated as a percentage. These are two very different numbers, because the heat output takes into account the lowest and highest output of the machine.

In the most basic terms, the stove's efficiency rating indicates how much heat and fuel is "wasted" going straight down the chimney flue.

If we give you an example, a stove with an efficiency rate of 80% loses 20% of heat and fuel in the combustion process. To compare and contrast, an open fireplace has an efficiency of around 30%, meaning 70% of the energy is lost.

So, on this basis, stoves are much more efficient than their fireplace counterparts.

Stoves in France are tested against French and European standards and, although there is considerable flexibility regarding the circumstances of each test, they provide a useful indicator. For the record, it should be noted that there is room for maneuver for:

• -The heat at which the test will be carried out
• -The amount of fuel burned during the test
• -How often is the stove refilled with fuel
• -Although it is not less than 45 minutes

The current process is simple. The designated tester will measure the temperature and carbon content of the flue gas. As the amount of fuel added to the machine is precise, these three elements are used to calculate the amount of heat and fuel that was lost (i.e. not retained in the stove), hence the calculation of the yield.

DIFFERENT MEASUREMENT CRITERIA

As mentioned above, some elements of the performance test may vary from manufacturer to manufacturer. In some circumstances this can make comparisons between stoves made by different companies not useless but somewhat less meaningful. It should also be noted that during the testing period the air supply (impacted by the stove vents) may also be manipulated although this is fully within the rules. In theory, it is therefore possible for stove manufacturers to achieve a certain level of efficiency by using their own parameters in the measurement process protocol. However, their machines still need to reach this level, so these are true readings.

Calculating heat and fuel loss through the flue is relatively easy to calculate assuming that an accurate measurement of the fuel added to the stove has been taken. The fact that the environment in which testing is carried out can vary from company to company can make direct comparisons between different stove manufacturers difficult, although this figure remains a useful indicator of effectiveness.

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