Burning overnight, what you need to know
Are you looking for the secrets to burning overnight in a wood burning or a multi fuel stove? Do you spend all day nurturing and crafting the perfect fire inside your wood or multi fuel stove, timing the refuel periods just right to maintain a good flame and heat output throughout the day only to go to bed and wake up the next morning having to do it all over again. Sound familiar? The good news is that it is possible to successfully keep a fire burning overnight so your home is warm when you wake up. We will share with you the secrets to achieving this in regular stoves, look at stoves that are designed to keep the heat in for longer and answer the question:
What are the dangers in burning overnight on my stove?
Okay, so lets start at the beginning, assuming that you are looking to burn for around 7hours overnight (say 11pm – 6am), while it is possible to achieve this remember the longer you leave the fire, the more likely it is to go out. Fuel and air are the two big factors that you need to get right in order to succeed, but other external factors such as high winds and cold outdoor temperatures will also factor in and can in some cases make it next to impossible to achieve. As with anything practise makes perfect when it comes to burning overnight, and it will often take several attempts to get it right, but that first feeling of success when you come down to a warm stove will outweigh the failures of the previous attempts.
Safety – Before we start we feel that it is important to say that while doing this is possible, leaving a fire untended for any pro-longed period of time is not recommended by us or any stove manufacture. So if you are looking to do this please proceed with caution. We have a checklist of safety tips further down the post which we would suggest you read before attempting.
Multi-fuel Stoves – Smokeless coal has a refuel period of approx 4 hours, under normal conditions, so by removing the air supply and replacing it with just a trickle of air you will be able to prolong this longer. Banking your stove up with as much smokeless coal as is safe to do so is vital to success here, as is ensuring that the vents on your grate beneath the fuel bed are open allowing air to seep up into the fuel bed. You should not go above the log retaining bar, and should not cover any air holes in the rear of the stove. There should also be space between the top of the fuel bed and the baffle plate. Ash is also a good insulator and tests have shown that placing a small amount of ash from the ash pan back on top of the coals prior to closing the stove down and going to bed can help to sustain the fire for longer.
Wood Stoves – Burning wood overnight is considerably harder to achieve as a typical charge will last 1-1.5 hours under normal burning conditions, so you will need to extend this by as much as 6 times, to last the night. Choosing the right wood is vital to success, it must be hardwood and have as lower moisture content as possible (read our guide about choosing the right wood here). Utilise the firebox space by using wood that is as close to the max length as will fit in your stove, and stack your wood so that there are air gaps between the logs, but keep the gaps as minimal as possible to maximise the amount of fuel you can fit in. Dedicated wood burning stoves, keeping a bed of wood ash in the base of the stove will also act as in insulator helping keep heat in the firebox. If your stove has a riddling grate see if you can position the openings in the grate so that they are closed. This will prevent ash from falling into the ash pan below and build up an insulator bed on top of your grate.
Air Supply – Next you have air regulation, when you first light your stove you will have all of the air vents open allowing as much air into the firebox as possible to assist in getting your stove lit and up to temperature. You almost need to do the opposite when it comes to sustaining a fire overnight, and will need to close off almost all of the air supply to your stove to try and slow the burn process down to a slumber/tick over mode. Depending upon which model stove you have this can be done differently and more completely then others. The more control you have over the flames when the stove is burning by adjusting the air controls, the better chance you have of maintaining a low burning fire for a longer period of time, remember you do not want to fully close all of the air supply on your stove, you need to maintain just a trickle of air into the firebox to achieve burning overnight.
So now your know the top tips on how to keep a fire in overnight on a wood or multi fuel stove is about mastering the air supply and loading your stove up correctly before going to bed. The question still remains, should you burn fuel in your stove in this way? What are the dangers in burning overnight on my stove? While the desire to maintain a low burning fire overnight may be appealing to prevent having to restart building your fire every morning. Is burning at low temperatures actually doing more harm to your stove, and would you be better off in the long run just relighting it from cold the next morning?
Primarily wood and multi fuel stoves are not designed for continuous burning and most manufactures will state in their manuals that the appliance is for intermittent use only. A big part of this is that room heating stoves are not really designed to be operated at low temperatures for extended periods of time. Stoves are meant to be run within their operating output range, when you burn at lower temperatures you will not achieve complete combustion, which will often result in unburnt logs of coal pieces left in the firebox. Another tell tale sign of incomplete combustion and low temperature burning is a milky or sooty residue left on the inside of glass. So this is what you can see, which while is an inconvenience is easily rectified by having a hot fire or cleaning the firebox, but it is what you can’t see that is the more worrying concern.It is the unseen the tar build up inside the chimney and high emissions/particulates that are produced due to the lower burning temperatures. High emissions and high particulate content is bad for the environment we live in and especially bad inside smoke control areas such as London that have higher levels of air pollution already. Tar build up if left unchecked will reduce the diameter of your flue/chimney and is one of the highest risks of chimney fires.
So, while the result may end up that you have a bed of embers left in ready for the next burn tomorrow morning, running your stove at a low temperature overnight might actually cost you much more in the long run than the time of creating a new fire in the morning.
So what can you do? Well if you are doing research before buying a stove, and would like to be able to burn overnight safely and cleanly then there are design considerations you can take into account before buying your stove. These “features” will allow you to safely maintain the firebox temperature for long periods of time so that you get complete clean combustion overnight and still have a warm flue and firebox temperature in the morning.
Insulation/Insulators – These can be the best way of maintaining firebox temperatures, so a stove made from cast-iron will take longer to heat up, but will also hold the heat longer as a result. Firebox linings can also play a part in maintaining firebox temperatures, there are different materials available from ceramic, to brick, cast-iron to fireboards. Stove manufactures Harrie Leenders have taken this a step further by creating their own firebrick material; Prestolith which helps better reflect the heat back into the firebox and thus maintain firebox temperature for longer.
Flue Temperature – Cold dense air sits a flue pipe and takes the most time to clear when establishing a fire, so maintaining some flue temperature will also assist in keeping a fire in overnight. If your flue pipe is insulated, i.e. you have a twinwall or double insulated flue pipe coming off the top of your stove, then while this can take longer to heat up due to the insulation, but it will maintain the inner flue pipe temperature for longer during and after the burn cycle. If your stove connects into a chimney, a liner helps with maintaining a consistent flue temperature from the top of the stove to the top of the chimney, this can be further increased by insulating the liner either by a wrapping it in a heat resistant and reflective blanket, or vermiculite granules. Chimney position will also play a factor as a internal chimney in the centre of two semi detached houses for example will be warmer than an external chimney breast that is exposed on three sides.
Heat Storage Systems – This is typically a man made material designed to absorb heat produced from the fire and slowly release it back into the room over a long period of time. Most stoves that offer a high top version can often offer heat storage material to fill this void and help to insulate the flue pipe as well as the firebox. More advanced versions feature this material built into them as standard, such as the Austroflamm Xtra system, which fills all voids with heat storage material making them as thermal efficient as possible without altering the external look.
Natural Stone Cladding – While this stone may look to be decorative, it provides a thermal insulator to the firebox. The thick stones sides absorb the heat produced from the firebox and slowly release that heat out to the room. The end result is that stoves with natural stone cladding on the sides and the top often boast that they stay warm for up to 8 hours after the fire has gone out. There are different levels of cladding available and different materials provide different levels of heat absorption. Weight is perhaps the best indicator for heat retention properties, knowing the weight of the natural stone, of heat storage bricks will give you a better indication as to how long it will continue to heat the room.
Specific Models – Some stove manufactures have thought about this issue and designed their stoves to achieve longer burning times and slow/slumber modes by adjusting their designs accordingly. Here are a couple of specific models that we are aware of that are designed to slowly and safely burn fuel for long periods of time.
The Stuv 30 wood burning series features a unique rotating door system where by the firebox can be rotated round so that only a sliver of glass is visible, insulating the firebox even further for long slow burning periods. To enhance this even further, Stuv 30-H models can be equipped with heat storage stones to help prolong the period of time that your stove can produce heat.
Dovre Tai and Saey 94 multi fuel stoves can be supplied with a coal hopper fitted to the top of the stove whereby you can load the stove up with more than a standard load of smokeless coal, and the hopper will feed the firebox with coal over a longer period of time. Combining the techniques outlined above with one of these stoves are ideal for burning overnight.
Pellet Stoves – The last thing to consider if burning overnight is important to you is a pellet stove. While yes this is not a wood burning stove, if being able to burn for long periods of time without having to refuel is what you are looking for you should defiantly consider a pellet stove, which can go for days at a time between refuelling. Furthermore many models can have timers and programmes set so that you can choose when the stove comes on and off. See our post about pellet stoves for more information on these stoves.
In Summary – If you already have a stove burning overnight is possible providing the conditions are right and your using the correct amount and quality of fuel combined with a limited supply of air. Doing so for long periods of time can lead to higher emissions and tar build up inside your chimney which if left can result in chimney fires. If your looking for a new stove, choose one that has as much thermal mass as possible, by looking into cast-iron, heat storage, or natural stone cladding. Alternatively consider the Stuv 30, Dovre Tai or Seay 94 models which have designed for long burning periods or a pellet stove that can last over 24 hours without refuelling.