Wood stoves are near the top of the list of home appliances that can be added to a home to reduce your monthly expenses and provide a comfortable heat to a home or cabin. If you have a reliable source of wood, you can heat almost for free (minus the time to cut, and store wood). I have used a wood stove to heat my home for over 40 years.This article will help people that want to start saving money with a wood stove or just enjoy the heat that a wood stove provides.
How do I regulate the temperature of a wood burning stove? The primary means of regulating the temperature of a wood burning stove is through the amount of air introduced to the firebox. There are many different types of wood stoves produced today including catalytic, non-catalytic, and hybrid models. Each type has its advantages and disadvantages but all types of stove rely on the amount of air that is fed to the fire to increase or decrease temperature.
Other factors have varying degrees of affect on the temperature of a wood stove’s heat output such as type of wood, dryness of the wood, wind speed, and many other small factors. We will start looking at this subject by taking a look at how wood stoves work in general and how specific stove types differ in heating.
The Chemistry of Fire
There must be three elements present for a fire to burn. The three elements are Fuel, in this case wood,Heat, and Oxygen. If you take away one of the three elements the fire will go out. Once the fire is started (the heat is applied), a wood stove is controlled by the amount of air that is introduced into the firebox. More air, hotter fire! Less air, less fire! It is not rocket science, it’s fire science.
Wood stoves have a device that controls the amount of air that is introduced into the firebox. Most older stoves employ some type of manual control. They have a lever, sliding vent, or valve that is used to open or close the air flow. The newer stoves have an automated valve that is controlled by a thermostat. Either way, monitoring the temperature of the firebox will assist in controlling the fire better and keeping your home safer.
The outdoor wind speed has a definite effect on the amount of air drawn into a wood stove. The output of a stove is through a chimney. This chimney must exhaust the fumes directly to the outdoors. When the wind speed increases, which is typical of a cold winter day, the effect on a stove can be dramatic. The wind across the chimney will draw more air out of the stove (up the chimney) thus creating a vacuum in the firebox and then drawing more air into the stove. This quickly raises the temperature of the fire.
With a stove that has manual control for air, the effect of increased wind could raise the temperature in minutes. If there is no automated control of the input air, the stove could burn out of control quickly. A digital stove thermometer (especially one with a high temperature alarm) could alleviate the problem before it becomes an issue. The alarm would alert the owner of the need to reduce the air flow to the firebox and thus reduce the temperature of the fire.
Low Temperature
The other end of the scale is a wood stove that has burnt up all its fuel (second part of the fire triangle) and is losing temperature fast due to the lack of fuel. This could happen overnight or after a brief wind event burns up additional fuel (wood) and is out of wood before expected. A low temperature alarm that is sent to a smartphone would save having to restart the stove and having the home reach a much colder temperature than desired.
Keeping the stove at a consistent temperature is key to keeping a home at a comfortable temperature. If a wood stove swings from too cold to too hot, this makes the output of the stove also swing too high and too low. An inconsistent stove temperature makes the objects in a home, the floors, walls, furniture, etc. also cool and heat. Once these objects have cooled down the requirement for additional heat to warm not only the air but also the objects increases the demand for heat from the stove.
This creates an overworked and inefficient system for heating. Keeping the stove consistent is the key to a comfortable home heating system. A consistent temperature in the wood stove creates a consistent temperature in the home and an efficient home heating system.
Fuel for the Fire
The type of wood you burn is the next most important element in the fire triangle. Different wood species have very different properties when it comes to burning. The denser the wood, generally the better it burns. Typically, hardwood trees that provide fruit or nuts are the best burning wood. The denser properties of the wood allow the wood to burn hotter, providing more BTU’s per cord of wood for longer periods of time.
There have been many studies completed on wood types and heat outputs. They are always measured in BTU’s per hour. The BTU (British Thermal Unit) has been used for years as the standard for measuring heat output in any heat producing appliance. Fuel is measured by taking the output of heat produced over time, generally an hour.
Burning wood that is at the top of the list of high BTU per hour will allow a wood stove to operate more efficiently. This also lets the owner of the stove get more heat out of the stove and fill the stove fewer times per day. All of these benefits are appreciated by the owner of the stove providing less work for more heat. Definitely a win-win situation!
Here is a list of the best hardwood to burn by BTU’s per hour.
Hardwoods and Their Statistics
| Species | Green Weight Per cord | Dry Weight Per Cord | Millions BTU’s Per Cord | Ease of Splitting |
| Apple | 4850 | 3890 | 27.0 | Medium |
| Ash, Green | 4180 | 2880 | 20.0 | Easy |
| Ash, White | 3950 | 3470 | 24.2 | Easy |
| Beech | 3760 | 27.5 | Easy | |
| Cherry | 3690 | 2930 | 20.4 | Easy |
| Dogwood | 4230 | 27.0 | Difficult | |
| Hackberry | 3980 | 3048 | 21.2 | Easy |
| Black Locust | 4620 | 4020 | 27.9 | Difficult |
| Maple | 4680 | 3680 | 25.5 | Easy |
| Sugar Maple | 3900 | 2750 | 19.0 | Medium |
| Mullberry | 4710 | 3712 | 25.8 | Easy |
| Red Oak | 4890 | 3528 | 24.6 | Medium |
| White Oak | 5570 | 4200 | 29.1 | Medium |
| Osage Orange | 5120 | 4728 | 32.9 | Easy |
| Black Walnut | 4584 | 3190 | 22.2 | Easy |
| Hickory | 5400 | 4650 | 29.2 | Medium |
Seasoning Your Wood
In addition to burning the best type of wood, preparing your wood to be burnt is critical to efficiently operating your wood stove. Proper preparation of the wood means storing and drying the wood or “seasoning” your wood correctly.
The fuel that a tree needs before it is cut down is water. Water is drawn out of the ground, through the roots and pumped up the trunk of the tree to the leaves. This needs to happen for the tree to continue to grow.
When the tree is cut down, the source of water is severed and the tree begins to die. This does not mean the moisture in the wood is gone. This moisture must be drawn out of the wood for it to burn efficiently. Some wood when cut down will have up to 85% moisture content. This needs to be reduced to between 15% – 18% for the wood to be ready to burn properly.
What is the best way to remove this moisture from the wood? First the wood must be cut to the length at which it will be burnt. It must also be split down to size for burning. This opens the log and provides more surface area which will allow air to pass over the wood and dry it faster.
Once the wood is cut and split, it needs to be stacked loosely so it is exposed to outside air as long as possible. Air and sunlight will evaporate the moisture out of the wood as it is stacked and waiting to be burnt. This is why a two to three year supply of wood is necessary to keep dry wood prepared for burning.
Using a simple moisture meter to test your wood before burning will assure that your wood is in the correct moisture range to burn. This keeps the higher moisture levels out of the stove where it collects particles and builds unwanted creosote on the walls of your stove and chimney.
Fire Needs Air
We have discussed the type of wood and the seasoning of the wood. Let’s take a look at how the air feeding the fire affects the burning process.
Assuming you have a high BTU wood type and have seasoned the wood properly, the flow of air into the wood stove is the primary controlling factor for the output of heat from a stove. Increasing the air flow to the firebox will increase the heat output of a wood stove. If the wood stove is maintained by a manual air inlet, small increases in air are advised. The heat will rise slowly but steadily once the air has been increased.
Closing the air vents should typically be done the same way. Small adjustments in airflow will allow for a slow drop in temperature also. Decreasing the temperature of a stove will take much longer as the heat in a stove is held for long periods of time in the firebrick and steel of the actual stove.
Knowing if the temperature of a stove is rising or falling is critical in each of these situations. Since the temperature rises and falls very slowly in each direction, having an accurate measuring tool is crucial.
The Best Thermometer
A thermometer should have the following characteristics. First it should be digital and read to the tenth of a degree. This assures that a minute change in temperature is noticeable. A tenth of a degree in temperature rise is very obvious when an air vent on a stove is opened or there is an increase in the wind speed.
The second attribute of a quality thermometer is a thermocouple that is capable of at least 1000 degrees Fahrenheit. The thermocouple is the device that is in contact with the stove and connects to the digital readout device. The thermocouple detects the temperature, transmits the signal through a cable to the digital readout device where it is displayed.
Ideally this thermocouple is magnetic so it can be placed anywhere on a metal stove. This allows the movement of the thermocouple to find the consistent hot spot on the exterior of the stove.
The need to read up to and survive over 1000 degrees Fahrenheit is critical because a stove can easily and quickly exceed this temperature if a creosote burn out of the stove occurs. This is when the creosote builds up in the firebox or chimney reaches a temperature that ignites the creosote and it flash burns.
This is another time when an immediate notice from a digital thermometer could prevent a chimney or even home fire. Closing the doors or air vents quickly is the best way to squelch the flames and drop the temperature quickly.
The last but definitely not the least feature that a digital thermometer should have is a connection to a WiFi signal. This allows the thermometer to send its data to an APP. The APP can then be viewed on any smartphone and gives the owner the ability to view the temperature of their stove from anywhere and receive alerts for high and low temperature events.
This gives the wood stove owner the freedom to leave the room where the stove is located or even leave the house as needed. With the ability to view the stove temperature from anywhere you have a cell signal (which is pretty much everywhere today), you are not tied down to watching a stove 24/7 throughout the winter months.
The analog, round, metal thermometers that are on almost every wood stove manufactured for the past 50 years will no longer be the standard found on stoves around North America. The new normal will be a digital thermometer that is connected to your smartphone.
Chimneys and Stove Control
Your wood stove chimney has a huge effect on the control of air leaving a wood stove. Maintaining a clean chimney allows the air to effectively exit the wood stove. If the air cannot exit easily, the air cannot enter properly.
One of the most important maintenance procedures that need to be completed on a wood stove is inspecting and cleaning the chimney. A by-product of burning wood is a substance called creosote. Creosote will build up in a chimney especially if the wood burned is not seasoned properly and has too high of a moisture content.
Creosote can build up in the chimney to the point of actually blocking the airflow out of the chimney pipe. This in turn stops the flow of air into the firebox. Typically if the fire is still burning, the smoke will back up into the home as it has to go somewhere. This usually happens when the doors are opened to stoke the fire. A large amount of air is introduced to the smoldering fire and the wood ignites as it has been air starved for a period of time. Smoke that cannot go up and out the chimney is pushed out of the stove through the open doors.
A regular inspection of the chimney pipe from top to bottom is recommended to keep this from happening. If the chimney is found to be coated in creosote, the chimney should be cleaned. If you do not have the proper tools and equipment (ladders, brushes, etc.), find a local professional that can clean the chimney for you. If you need more information on chimneys, see my post: How can I Reduce Creosote Buildup in My Chimney?
Housekeeping
No, I am not going to get you in trouble with your wife! I am talking about cleaning your stove. A wood stove burning, sends most of the elements of the fire up the chimney. Newer stoves are capable of eliminating well over 93% of the particles by reburning many of them. This still leaves a pile of ash in the stove that must be emptied out at some point. Again, the better the wood and the closer the moisture content to the ideal (15%-18%), the less ash you will have to clean out of the stove.
Cleaning this ash out is not only necessary for room in the stove, but is helpful in making the stove more efficient. The buildup of ash eventually absorbs heat that should be sent to the home. Too much ash also will reduce the space in the firebox (more important in small stoves) which in turn limits the amount of wood you can load in the stove. Less wood means a shorter burn time which can really be an issue when you want a long burn overnight.
Why is Regulating the Temperature Important
Keeping the temperature of your stove consistent is not only a safety issue, but is also a stability issue for the temperature of your home. Once a home cools down, it takes more energy (heat) to raise the temperature back to normal. If the stove cools, the resultant temperature of the floors, walls, furniture, etc. all drop. To bring all these items back to the desired temperature takes more energy than it takes to maintain these items at a consistent temperature.
The ideal is to keep the output of the stove at a stable temperature which means the fire needs to be maintained at a steady temperature also. To accomplish this, the stove needs to be monitored to ensure the firebox is properly stoked with wood and the input of air is sufficient to burn at the required temperature.
Conclusion
Regulating a wood stove temperature can be accomplished by a few simple procedures.
- Using the best wood you have available with a high BTU/hr will help regulate your wood stove. Choosing your wood carefully (rather than whatever you can get) is recommended.
- Seasoning your wood for 15%-18% moisture content will provide a best case burning scenario for heat output.
- The airflow into your wood stove is the primary means of controlling the temperature of any wood stove.
- Monitoring your stove with a digital thermometer will allow you to know and react to any change in your stove’s behavior. See TempSure.net for the best wood digital thermometer.
- Check and clean your chimney and stove regularly.
Additional Questions
Should I draw outside air to feed my wood burning stove? Drawing outside air should make your stove and your home more efficient. Before doing this make sure you check with the manufacturers’ recommendations on installation and maintenance.
Are wood burning stoves safe today? When operated safely, a wood stove is as safe as a furnace based on statistics from the fire safety institute.