Chimneys Part 1: What’s Your Chimney Done For You Lately?

Once I started in the stove department I was surprised at how little I knew about the fire raging in the middle of my house. There’s a lot to know – this is the first in a series of articles explain what’s going on with your stove & chimney.

Most people don’t realize the chimney has as much or more to do with how the stove runs than the stove itself!

A wood stove (fireplace, etc) is a safe place to turn wood into fire and smoke. How the appliance is designed will affect how much heat is harvested into the house and how much pollution comes out of the chimney. But it’s the chimney that determines how (& why) your stove works.

Your heater needs a chimney like your car needs an engine, it won’t go without one.

Chimneys work like a hot air balloon. The balloon is filled with hot air until it is warmer and more buoyant (lighter) than the cooler air around it, so the balloon rises. Smoke in the chimney is hotter and lighter than the air outside the house, so it rises – same concept. So get this – the colder it is outside, the better the chimney will draw and the stove will work (there are exceptions, of course).

So smoke gets sucked from the firebox which has to replace that air from somewhere. Fresh air gets sucked into the stove from the house or an outside air duct and feeds the fire. If there is a weak draw in the chimney, you will get a weak supply of air for your fire.

Some facts about how chimneys work:

  • The taller the stack, the stronger the pull. In some cases a small stove on a tall chimney needs a damper so that the chimney doesn’t pull too hard & over-fire the stove. You can increase the draft of your chimney by making it taller & many stove manuals list a minimum chimney height.
  • A chimney inside the house (or in an insulated chase outside) will work better than an exposed outside chimney that will always try to cool to ambient temperature.
  • If the stove’s been out for a while & everything is cold, pre-heat the chimney before lighting your kindling. Light a few pieces of newspaper in a spot where the smoke will go right up the chimney. That heat will get your draft started. Experiment to find out how much newspaper you need to use to get the fire to reliably go. One of my customers keeps a hair dryer near his stove & shoots it up into the chimney to pre-heat it. Apparently it works well & fast.

New stoves & old chimneys sometimes don’t mix. People who are upgrading from their old Fischer or other ancient stoves to a new high-efficiency appliance find their chimneys don’t work as well. It’s a phenomenon plaguing many homes. See, a pre-80’s stove lost 45% – 65% of its heat up the chimney. Smoke that hot made any chimney work well. Now stoves only give up 18% – 25% in the chimney – way less heat (good news is you’re harvesting that heat into your house). More consideration has to be given to the chimney system with a newer, more efficient stove.

The next articles will deal with forces inside and outside the house that act on your chimney and make your stove sometimes work better & sometimes worse.

For answers to your specific stove and chimney questions call me at Gray Creek Store – 250 227 9315.

By Dan Silakiewicz

 

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