Combustion And Draft In Your Chimney
When Basic Chimney Sweep & Repair technicians come to your home for a chimney sweeping appointment, you’ll probably hear us talk a lot about byproducts, and creosote, and the combustion process. Those topics are kind of the basic building blocks of why chimney sweeping is so important — combustion in your fireplace creates byproducts, including creosote, which build up on the flue walls, affecting draft, potentially damaging your flue liner and, if left unswept, leading toward a fire hazard.
It’s good to know about the combustion process and how draft occurs so that you can prevent accidents related to your chimney
If you’ve ever wondered how the combustion process works inside your fireplace or flue, you’re not alone — we give a fireplace and chimney combustion rundown to a lot of clients, because it helps to have a sense of how things work when you’re trying to make informed decisions about the care of your chimney system.
Here are some of the basics:
Combustion In Your Chimney System
Combustion, at its most basic, is burning — or, if we’re talking the dictionary definition, a speedy chemical process that results in heat and light. When we’re focused on your chimney system, by referencing combustion, we’re talking about the process of burning fuel inside your firebox — be it wood, wood pellets or gas. You start your fire or hit your gas ignition switch, the fuel burns, heat and light result, and you get what you’re looking for out of your fireplace or stove.
Heat and light aren’t all that follows, though, and as chimney technicians, our job has a lot to do with keeping up with the other stuff — namely, byproducts and draft.
Draft And How It Occurs In Your Chimney
Draft is the force that pulls heat and byproducts up your flue, and out of your home, so proper draft is key to your chimney’s function. It occurs in your flue because of a principle we all know well: hotter air rises, and cooler air sinks. Air always moves from an area with higher pressure to lower pressure, and aressure difference occurs while combustion is happening in your fireplace or stove — hot air rising in your flue creates a lower-pressure area below, and that pulls in cooler air near your firebox opening, and draft moves along as it should.
What Can Impede Draft?
Issues with smoke, stains, odors and improper burning in your combustion appliance often have something to do with impeded draft. The specific culprits behind that impeded draft, though, can vary.
It could be something simple, like a failure to open your chimney damper all the way, or a lack of sufficient combustion air (that lower-temperature air getting pulled into your firebox). The latter happens a lot in homes with well-sealed energy-efficient windows and doors, and if cracking a window when you have a fire clears up the issue, you’ve found your culprit.
Draft problems could also be due to a size issue. A chimney that isn’t the correct height won’t achieve the right level of draft, and a flue that’s too big or too small in diameter will lead to draft issues, greater byproduct production and less efficient burning, among other issues,
Often enough, Basic Chimney techs find that draft issues are the result of flue liner damage. If your flue liner is cracked, or spotted with voids or gaps, it limits the force of your draft. Think of it kind of like a straw: Apply some force to an intact straw, and your drink comes right up; try with a straw that has a hole in it, and you’ll struggle and struggle with little success. That’s why it’s key to have your chimney inspected annually, and to have flue liner damage taken care of as soon as possible.
If you have any questions about combustion or draft in your chimney, Basic Chimney Sweeps is always here to help – just give us a call!
