Stove efficiency can drop to as little as 20% if any number of things are wrong with the chimney!

 “Your Chimney is more important to understand than your stove!”

The EPA has instituted some rules regarding wood and pellet stoves to improve air quality standards and to reduce emissions, but is that what the problem is? The rules became law on May 15, 2015 but don’t expect to see changes in your local hearth store until Jan. 1, 2016. This rule is a NSPS – New Source Performance Standard. Owner’s manuals will be updated with information on how to run the stoves more efficiently. Wood stoves will be tested and certified to a standard for improved consistency. Improvement to chimneys will help reduce emissions. Pellet stoves will need to also meet a standard and while the standards have changed most pellet stoves already meet or exceed that standard. Pellet fuel will be tested and labeled to a standard which will improve the fuel used. Improved air quality and reduced emissions are good goals but these rules may not be addressing the real problem, in fact they do nothing to address CO2 levels, it is not known if those standards are coming.

A local dealer of wood and pellet stoves, Dave Wiggers in Youngsville Pa., believes the chimney is more important to understand than the new EPA rules. Chimneys are required for stoves; wood, pellet or gas, and that is where most people’s understanding of them ends. Just as a race car needs a good engine it also needs the proper exhaust system to reach peak efficiency. Chimneys also do more than provide a method to vent exhaust. A properly sized, designed and installed chimney can improve stove efficiency, reduce fuel consumption, prevent chimney fires and reduce emissions. Remember that Indians lived in their chimney, a teepee, because they burned clean.  The chimney has not been given enough credit for its role in heating system performance yet it is as critical as the stove itself. So what is a good chimney?

Let’s look first at how we get bad chimneys. Chimneys are installed when building a new home without knowing what type of stove will be used. In most cases the contractor will install a “big” chimney thinking that will be able to work for any stove. A stove with a properly sized and insulated chimney may be replaced with a different unit requiring a different sized chimney, but due to costs or lack of understanding the chimney is not changed. Age or improper sealing during installation may open up air leaks in the chimney and create a bad chimney, $4.50 furnace cement could solve a lot of these issues. Good chimneys do not allow excess air in as that will decrease the draft and cause creosote or destroy the stove, bricks and gaskets due to excess draft. The industry has also designed and built more efficient stoves, catalytic stoves for example, these newer stoves have lower flue gas temperatures and are less tolerant of “oversized” chimneys or those with leaks.

How does the chimney work? In order for a stove to operate it first is started and then as it heats up the chimney will be heated. Once the chimney is up to temperature then a ‘thermal lift’, or draft (heat rises), is created causing fresh air to be pulled into the stove, fuel to be burnt and gases exhausted. This process is “tuned”, like a race car, by the manufacturer who has designed the stove with an exhaust port (chimney) that will allow for the air to move through properly and burn the fuel in the most effective process. The chimney of a stove has the greatest control over the balance in the system. Too much air flowing thru will cause the air to cool in the chimney, allowing creosote to build up, and potentially cause a chimney fire! As Dave Wiggers says; “Creosote is not the real problem, the real problem is not understanding what causes creosote. Too large a chimney, and leaky clean out door, are major cause of creosote…”  Likewise if the chimney is to small the stove has to work harder to burn the fuel due to not having enough air. In either case the stove does not produce the heat that is desired and problems will result.

So which chimney is best for your needs?  The answer lies in the type of fuel you are going to burn, and what type of stove is going to be used. Wood stoves typically have either a 6” or 8” flue and while 2” does not seem a lot the increase is almost double in area. A chimney must be balanced to the stove so that both can operate at peak efficiency, allow for maximum heat from the fuel and to do it safely. Three categories of chimney systems exist, solid pack double walled, triple wall insulated, and 3 walled air cooled. Industry and third-party tests show that there is not a significant internal temperature difference between the solid pack double wall and the more expensive 3 wall air insulated systems. The only type of prefab chimney NOT recommended for wood stove or furnace use would be the complete thermo-system. These designs were made primarily for zero clearance fireplaces and freestanding decorative fireplaces. They would probably run too cool for slow burning wood stoves and would cause significant creosote build-up. The final answer on the best chimney is that you, your dealer/retailer and installer, need to understand the heating system; stove, chimney, your home structure and area to be heated. It is also important to inspect the chimney frequently for creosote deposits or air leaks, and to regularly clean the chimney and stove!

Fresh air for your all stoves becomes as issue as you button up your older home, or as newer homes become more air tight. Adding a fresh air supply from outside the home can improve the efficiency of the heating system greatly! Balancing the whole system will help insure that you stay safe, warm and comfortable. Do not sacrifice any part of the system for short term cost savings! If all stoves had the proper chimney, emissions would be reduced worldwide, stoves would last longer, fewer homes lost to fires and many lives saved.

The EPA has started the process of educating the industry, but more needs to be done. The industry and consumers need to understand the chimney, and how it is an integral part of the overall system working efficiently. The saying goes that you cannot legislate morality or common sense, so perhaps the EPA and the industry need to do more to educate themselves and the consumer on the importance of the chimney. Maybe someday we will all be able to live in our chimneys again.