Why does my wood stove's glass get sooty?

Is the glass of your wood stove getting excessively dirty? Here are 3 possible causes, and what you can do to fix it!

1- The moisture content of your wood is too high.

Solution: Make sure you use good, seasoned cord wood. The wood you burn plays an important role in the overall performance of your heater. Your wood should have been properly dried for approximately one year. Storage is also key. Wood that has been cut for one, two or even more years, will not necessarily be dry if it has been stored in poor conditions. Under extreme conditions, it may have rotten instead of drying. Smaller pieces of wood will dry faster. The wood should be stored in a place where the grass is not too long, and where the wind will be able to circulate between the logs. A 12-inch gap should be kept between the cords. The wood should be placed in the sunniest area and should be protected from the rain and snow on top, but not on the sides. Use a moisture reader to measure the moisture content of your wood. Ideally, it should be below 25%.

2- The logs are positioned too close to the glass and are obstructing the air flow that is necessary to keep the glass clean.

Solution: Make sure to keep a minimum gap of 2 inches between the logs and the glass.

3- The chimney draft is too weak.

Solution #1: In many cases, a weak draft is simply due to insufficient heat in the exhaust system. Build a small, intense fire, and leave the door ajar (never leave the heater unattended). Before inserting larger logs, use dry kindling to obtain a good bed of red embers. Gradually increase the size of the logs. Close the unit’s door when you reach a flue temperature of approximately 475 °F on the chimney thermometer. Leave the air intake fully open for approximately 15 minutes. Then, gradually close the air intake control. Note that there is no danger in letting the temperature inside the flue reach approximately 700 °F during the start-up. This is even favorable in order to properly start your heater. You must, however, avoid maintaining excessive temperatures (above the comfort zone on your thermometer) during a long period of time. Your chimney thermometer should be positioned on the exhaust pipe, approximately 18 inches above the unit.

Solution #2: Your heater may not have all the oxygen it needs to allow for a sufficient draft. You first need to insure that the room where the heater is located is sufficiently large and well ventilated. Open the nearest window by approximately 2 inches. If you notice a significant improvement, it is a sign that the unit needs more oxygen. The room may be too insulated or too small. Without an additional source of oxygen, the draft will remain weak and cause the glass stay dirty.

Solution #3: The chimney may be too short. In order to obtain a sufficient draft, your chimney must have a minimum height. Twelve feet (from the heater to the chimney cap outside the house) is a minimum. A height of 15 feet or higher is ideal.

Solution #4: Your exhaust system may be too tortuous or may lack a sufficiently steep slope. Ideally, your exhaust system should not have more than one 90° elbow. Furthermore, all horizontal sections should be as short as possible and have a minimum slope of ¼" per foot.

Solution #5: Your exhaust system may be oversized. When your chimney is oversized, the volume of air that needs to be warmed-up is larger. It is therefore difficult to reach temperatures that will allow for a sufficient draft. Most advanced combustion systems (those certified to EPA/CSAB415.1-10) have a 6" flue outlet (152 mm). If your exhaust system does not have a 6" diameter, a solution is to insert a stainless liner with a 6" diameter inside the exhaust system.