Maintaining your chimney; truth about oil-fired condensing boilers

Alaska HomeWise: Ask a Builder

By Cold Climate Housing Research Center Staff

The “Ask a Builder” series is dedicated to answering some of the many questions Fairbanks residents have about building, energy and the many other parts of home life.

How often should I clean my stovepipe?

How often a chimney or stovepipe should be cleaned is case dependent. If you have more than an eighth inch of creosote buildup inside, it should be cleaned out. In order to determine how often you should clean your stove, burn wood on your regular schedule and go on your roof and look down the chimney pipe every so often. After some time you will see creosote buildup on the inside of the chimney. Clean out the stack and continue your schedule. With regular monitoring, you will start to get an idea of how quickly the stack builds creosote and how often you need to clean it.

In addition, if you have just bought a house that has a chimney and a wood stove, make sure you get a thorough inspection. Just because a stove did not burn the house down previously, does not mean it will not happen to you. Get as much information as possible about how the stove operates and if every component is properly sized before you start using it. Be especially wary of a stovepipe that goes through a back wall rather than up through a roof. Pipes that go through a wall have more problems with drafting because they bend after coming directly out of the stove, which reduces airflow. They then go immediately outside where they are not insulated, so the combustion gas cools quickly and has a harder time exiting. Sometimes this configuration can create a “cold plug” because it takes a lot of energy for the stove to warm up the pipe and create a proper draft. Cold plugs can contribute to backdrafting as well. Any time smoke does not exit the pipe properly, it can also create more creosote.

I heard that the condensate produced by new oil-fired condensing boilers contains “strong acids” and they should be avoided for that reason. Any truth?

The CCHRC facility has a Monitor FCX oil-fired condensing boiler. We use a site-made trap of black ABS 3 inch drain fittings filled with limestone chips. This neutralizes the condensate before we discharge it to the sewage treatment plant that is in the basement of our facility. We have had no problems at all with the condensate from our boiler.

The LifeWater Engineering facility is heated by a Monitor FCX oil-fired condensing unit with the condensate drained directly into the sewage treatment plant the serves that facility. They have not been able to detect any change in the ph of the waste water system with the addition of the acidic condensate. The boiler itself uses a high grade of stainless steal and polypropylene exhaust components that can handle the acidity without any problems.

The acidity of this condensate is around that of very acidic wine. A ph test strip for pool water or hot tub water would give you some info on the acidity of the condensate from the fuel you are using.

Alaska HomeWise articles promote home awareness for the Cold Climate Housing Research Center (CCHRC). If you have a question, e-mail us at You can also call the CCHRC at (907) 457-3454.


Comments are closed.