Frequently Asked Questions
- What is the big deal with ‘closed (or slow) combustion’ fireplaces?In short, closed (or slow) combustion refers to the ‘discovery’ many years ago that burning solid fuel in a closed metal box can increase the heat output and at the same time reduce the fuel consumption compared to a traditional open fire.
Instead of throwing fuel into a freely oxygenated fire where it is chewed up very quickly and much of the heat lost up the chimney, you get to control how much oxygen your fire gets with various air vents on your stove. This means that you can optimize your burn to maximize heat output and reduce fuel consumption in comparison to an open fire.
In addition, burning the fuel in a robust stove means that your fuel can achieve a much higher temperature than it would if burned in an open fire. This is another bonus as you require less fuel to achieve the same output.
These stoves can easily be ‘retro-fitted’ into any home. You do not need to build a big chimney stack and fire surround.
Another big ‘plus’ is the fact that your fire is safely contained so that you can fire it up, close the door and go to bed, leaving your heat to radiate well in to the early hours!
- What is secondary and/or tertiary burning?Basically, it is the process by which volatile gases that would normally be emitted up your chimney are re-ignited inside the stove creating more heat and better efficiency and cleaner emissions from the same piece of fuel. Secondary indicates that a second ignition takes place, tertiary indicates that a third ignition takes place.
However, do not be ‘blinded by science’ when you examine and compare your stove manufacturers. A fair comparison can be based on Kilowatt Rating (KW) and Efficiency rating.
- What does ‘Kilowatt rating’ mean?Sorry but we have to get a bit ‘heavy’ here so bear with us!
1 Kilowatt is equivalent to approximately 3,600 BTU (British Thermal Units). A BTU is equivalent to 1,055 ‘joules’ which is now the internationally recognized measurement for this type of energy.
The reason we mention BTUs is because a BTU was traditionally used as a measurement for the thermal energy required to heat 1 pound (453 grams) of water by 1 degree Fahrenheit (approx. 1.8°C).
So, a Kilowatt in terms of thermal measurement is considered to be 3,600 times more than the thermal energy required in this simple experiment heating water.
Ok so far?…
Well, the Kilowatt rating on your stove is not simply the thermal energy being output by your stove. The stove itself does not produce any thermal energy in it’s own right – it is just a metal box.
Really, the KW rating on your stove is more like a measure of the ‘ideal’ thermal output that your stove can maintain during the burning process inside it whilst maintaining a certain level of efficiency and without prematurely damaging the stove body or internal components.
Warning! Stove manufacturers will choose what data suits the market they are targeting and publish accordingly.
For example, a stove rated as 12KW and 75% efficiency during the test process may comfortably be able to kick out 16KW without too much trouble. However, the efficiency at 16 KW may be reduced to 70% which does not suit the manufacturer’s target market so they publish the results based on the 12KW figures.
- What happens if I burn my stove too hot?To start with, you will wear through your fire grate and throat (baffle) plate prematurely which could be a costly and unnecessary replacement.
In addition, evidence of ‘over firing’ will likely invalidate your warranty in the event of damage to the body of the stove. This is the case with any stove manufacturer.
‘Over-firing’ is a common mistake made by new-stove enthusiasts. Generally, the new user believes that he should have a raging inferno at all times, when in fact, the burning process should be ‘slow and steady’ not ‘hard and fast’.
An easy way to avoid this common misunderstanding is to use a stove pipe thermometer until you get used to regulating the heat from your stove. We supply them and they work on any stove.
If used and maintained correctly, your stove body will last you a lifetime. Internal components will normally require replacement over a 5-10 year cycle.
- What is the ‘efficiency rating’?Well, you did ask!
This is supposed to be the measure of how much of a fuel’s latent energy is given to your room during the burning process. The ‘scientists’ set a measure for the amount of fuel to be used (weight etc) and how often the refueling will take place. They will test the emitted flue gases in the flue pipe (chimney) for temperature and carbon content during the burning process allowing them to calculate how much energy contained in a given fuel has not been radiated from the stove to the room compared to how much has been. The difference gives you a percentage rating for how efficient the stove is. E.g a stove with 75% efficiency rating is effectively transferring 75% of the energy stored in the fuel consumed to heating the room.
This is useful in principle. The problem is that each manufacturer may use their own test conditions to measure the efficiency which makes it very subjective! Even within regulated countries, they can choose what fuel, how much fuel, refueling times and oxygen intake they want to use under the test conditions, provided they publish this information.
This makes it close to impossible to measure exactly ‘like for like’ as you do not know what the test conditions set by the manufacturer are.
However, the good manufacturers (like Charnwood) will publish their test conditions and refueling times which means that you have a much more genuine result and can make a better comparison with others (provided they also publish their test conditions). In addition, all Charnwood stoves comply with EN13240 or EN13229 which set down some basic principles of efficiency as a minimum. In addition, all Charnwood stoves are leading the way in terms of compliance with ‘Eco-Design 2022’ which raises the bar for clean solid-fuel burning standards to its cleanest in Europe ever.
- How are Charnwood stoves tested?All Charnwood stoves are tested to meet EN13240 and EN 13229. These are European tests. Among other things, these tests require the appliance to achieve the following standards:
Be soundly constructed
Have means of cleaning their internal flue-ways
Be provided with a glove or tool for handling hot surfaces
When operated according to the manufacturer’s instructions, have an efficiency of at least 50% (Charnwood stoves range between 71% and 82%) and CO emission <1%
Need refueling no more than every 45 mins. on wood, 1 hour on mineral fuels (intermittent use)
Be capable of burning unattended for 10 hours on wood, 12 hrs on mineral fuel (if for continuous use)
Be marked with a label showing the maker’s name or mark and the model, plus relevant performanc data
This is extremely reassuring as you can be assured that your Charnwood stove will meet your expectations!
Some manufacturing areas of the world (such as developing economies and cheap producers) may readily sight high efficiency ratings and KW outputs but one should be cautious when presented with impressive statistics from relatively cheap products. Like most things in life – you get what you pay for with a stove.
- What is the best fuel to burn?We are advocates of wood. Plentiful in supply, sustainable and affordable. You can burn many other fuels on your Charnwood stove but wood is our preferred fuel. Your average tree will consume more carbon dioxide during it’s lifetime that it will produce when burnt in an efficient closed combustion fire place. Our fireplaces work exceptionally well with semi-hard, well seasoned non-resinous woods such as eucalyptus (blue gum).
- What flues should I use?Flues are currently not regulated here in SA so you can even find ‘galvanized’ or low grade stainless steel products on the market. Be cautious of these as you will get issues with leaks, corrosion and smoke which will dampen your fireside experience. Speak to your Charnwood distributor who will offer a full detailed quote fro supply and installation.
As a basic, we recommend an ‘entry level’ grade 304 product (the non-magnetic type if you want to do a quick check with other available products).