Stove efficiency

On our website we show an efficiency rating for many stoves. We only list this because it is the "Standard" measure of efficiency in the UK and EU. The efficiency rating is not reliable for comparing stoves to each other.

What is the efficiency of a stove?

The efficiency of a stove tells you how much of the energy in a fuel will be given to the room when you use the stove.

How efficiency of stoves are measured

In line with the BS and European EN standards the efficiency of stoves are now measured in the following way:

1. The manufacturer gets to specify a refuelling period, with a minimum period of 45 mins and no upper limit.
2. The manufacturer gets to specify the heat output to test at.
3. The manufactuer can also specify the size of the fuel (within reason) - but apparently this rarely happens (I spoke to a technician at Gastec at CRE Ltd where they test a lot of stoves in the UK)
4. The efficiency is then calculated as the average efficiency over the period.
5. The flue gas temperature is measured as well as the carbon content of the flue gases. This allows the wasted heat and wasted fuel to be known, because there is a known quantity of fuel being burnt this allows the efficiency of the stove to be calculated

This means that if the manufacturers wants their stove to appear to be very efficient all they have to do is change the refuelling period and the heat output to test at to get the efficiency they want.

So this means that:

1. You cannot compare the efficiency of stoves with each other as they are all tested with different refuelling periods and with the air vents open to varying degrees.
2. The end user is not really left with a way of knowing how efficient the stove is going to be (other than when running under the specific conditions of the test).

For more information about the stove heat output test see our stove heat output page.

As an example have a look at some examples of stove test result anomalies.