Stove efficiency – it affects every owner, just what is it?

It is something you will likely come across when it comes to buying and owning a stove – efficiency. However this is a term that has been banded around for as long as stoves have been sold, yet it can be confusing to pinpoint what exactly it means.

In short, the more efficient a stove is, the more heat you get from your fuel, but with less emissions. However, a number of factors apply when it comes to efficiency which can impact your experience with your stove.

You would think that a higher efficiency rating on a stove the cleaner burning it is with less emissions with greater fuel efficiency, but this is not always the case. To begin with, let’s take a look at two of the most efficient stoves in the world.

Which is the most efficient stove?

Burley Debdale 4

The most efficient stove on is the Burley Debadale 4, coming in an impressive 89.8% efficiency.  The reason it is so efficient is due to a trap at the top of the stove. This trap burns off many soot and particulates heading towards the chimney, burning them and giving even more heat.

The thinking behind this is that the longer you can keep the smoke in the stove the more of it you can burn off, thus helping the overall efficiency of the stove. Hot air is injected through the sides of the stove creating a vortex of whirling flame, raising the internal temperature and ensuring there is plenty of heat on the trap.

burley stove, internal, air flow
The internal workings of a Burley stove

Close on the heels of the Burley Debdale 4 is the Stovax Huntingdon 40 which has an efficiency of 88%, but has been around for more than 10 years! But this is where the testing process can become somewhat subjective – and the reason why you should not base your decision solely on efficiency. Take a look at the chart below comparing the key aspects of these two stoves:

Burley Debdale 4 Stovax Huntingdon 40
Net efficiency 89.80% 88%
CO concentration in emissions 0.28% 0.21%
Output 4kW 9kW
Flue Gas Temperature 156°C 273°C
Stovax Huntingdon 40 efficient stove
Stovax Huntingdon 40

So whilst it is simple to claim the Huntingdon 40 is almost as efficient as the Debdale 4, is is not entirely true. A key element here is that such efficiency with the Huntingdon 40 is only achievable by burning solid fuel briquettes with 9kW of heat being put into the room. This is quite a lot of heat, and a lot of fuel to get it up to that temperature.

However the Debdale 4 produces 4kW of heat burning only wood. Also, the Debdale 4 has less heat going up the chimney, as indicated by the flue gas temperature. This means that most of the particulates are being burnt off before they can go up the flue.

So now we know these are highly efficient, let’s look in to how they can be so efficient.

An air tight stove helps efficiency

An air tight stove means air doesn’t enter the stove in places you don’t want it to, such as around the door or through the air controls when they are closed. This helps efficiency as you are able to greatly control the flame and the speed of the burn.

Air supply is vital

New builds can be too air tight for a stove, consider external air supply

Dependant on how well the primary air vent supplies air to the fire is an indicator as to how efficient the stove is. The better the air supply, the hotter the fire can burn, meaning less particulates leaving the stove, up the chimney and out into the atmosphere.

If a stove was put into a tight opening with a central rear inlet for air, the amount of air a stove has to burn is reduced, which effects efficiency. Air flow around a stove plays a big role, it has to have plenty of air to draw from the room to help give a more complete combustion.

A room, particularly is if it is a new build, which can be very air tight, has a limited amount of air in it. A stove needs a constant supply of air to burn effectively, so if the room within which you wish to install the stove is small, it can be worth considering an external air supply, which will allow the stove to draw all the air it needs from outside. If this is not a suitable alternative, consider adding air vents into the room from outside.

Similarly, a stove needs enough air around it to circulate the heat. In a tight space, the air can gather around the stove, which means not as much of it is being put back into the room. A stove top fan is a good and simply way of moving hot air away from the stove.

Fuel quality is important

Not exactly a factor associated with the stove efficiency, but the quality of the fuel you use in your stove will greatly affect the overall end waste product and running costs.

Poorly seasoned wood, with a high moisture content, will burn slower and with less heat, as the fire expends it energy boiling the moisture out of it. Not only is this a waste of your fuel, it can lead to a dangerous build up of creosote in your chimney, which could cause a chimney fire. Here is a blog post about the importance of seasoning wood properly. This adds to the overall efficiency of a stove, but doesn’t necessarily contribute to the efficiency rating.

Well seasoned, dry fuel is important for an efficient burn

Overall, it is important to take stove efficiency into account when you come to choose your stove, but be sure to look at it subjectively. The rating is only as good as the tests that were performed on the stove, with many test-houses testing the stoves under optimum conditions. Efficiency can be affected by any of the above factors. It should not be the only element of your consideration, but it is important to understand it.

As a general rule of thumb, DEFRA approved stoves are highly efficient, with very low emissions, enabling them to be burn wood in smoke controlled areas. Take a look at our selection of DEFRA approved stoves today!

If you have any questions, get in touch in the comments below!

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