The world of wood heating has a lot of jargon. If you’re new to wood-burning appliances, the question, “How many water column inches of static pressure should be in a wood stove’s chimney flue to ensure a good draft that prevents creosote?” will probably draw a blank stare.
And if you’re thinking of buying a wood stove, a pellet stove, or a wood-burning furnace, all of these technical terms can be a little intimidating. There’s a lot to learn.
At the same time, though, all the complicated lingo shouldn’t stop you from diving into the wonderful world of wood heat.
At HY-C, we’ve been manufacturing forced-air wood-burning furnaces for over 40 years. And in this guide, we want to cover some of the most commonly used terms in wood heating to help you understand what it all means.
By the time you’re finished here, you’ll be much more well-versed in the vernacular of wood heating products. And of course, you’re welcome to bookmark this page and refer back to it if you ever run into trouble.
Wood Heating Glossary (click to jump to a term):
A
Ash
B
BTUs
C
CFM
Chimney
Chimney cap
Class A chimney pipe
Clearances to combustibles
Cord
Creosote
S
Seasoning
Secondary combustion
Softwood
Spark arrestor
Static pressure
W
Water column inches
Wood furnace
Wood pellets
Wood stove
Wood Heating Terminology Defined
Note that the terms covered here are listed in alphabetical order.
Ash
Ash is a solid, powdery residue left behind from burning wood. Most wood heating appliances have a grate in their firebox that filters ash down into an ash pan — a separate compartment in the appliance designed to hold accumulated ash.
This ash pan needs to be cleaned periodically to ensure the appliance continues to function properly and efficiently.
BTUs
British thermal units, or BTUs, are one of the most common terms used in wood heating. Their true definition is, “The amount of heat energy needed to raise the temperature of one pound of water by one degree Fahrenheit.”
In the wood heating world, BTUs act as a quantifiable indicator of the amount of heat energy an appliance can deliver. Simply put: Higher BTUs mean more heat delivered. Our guide to BTUs covers the subject in much greater depth.
CFM
Cubic feet per minute, or CFM, is used to refer to the amount of air that a blower motor can move in a minute. Many wood heating appliances (especially wood burning furnaces) utilize a fan to push their heat through a home. The higher the CFM of that fan, the more heat it can move around.
Chimney
A chimney is one of the most important components of a wood heating system. It’s the structure through which combustion byproducts (like smoke and carbon monoxide) are filtered out of the home.
A chimney should not be confused with a flue, which is a smaller part of the whole chimney system.
Chimney Cap
Typically situated on a chimney flue, a chimney cap consists of metal mesh topped with a flat metal hood. Its job is to keep precipitation and nuisance wildlife from entering the flue while preventing downdrafts and arresting sparks. Our chimney cap guide covers these caps in depth.
Class A Chimney Pipe
Class A chimney pipe is a durable, fire-resistant type of metal pipe commonly used in wood stoves, pellet stoves, and wood furnaces. It’s easier to install than traditional masonry chimneys, which makes its use popular among appliance installers.
Clearances to Combustibles
Clearances to combustibles are the distances from which specific parts or sides of a wood heating appliance must be kept from flammable materials.
These distances typically change from appliance to appliance. They also tend to change for different sides of the same appliance (i.e., the side of a furnace vs. the back of that furnace).
Cord
A cord is a unit used to describe an amount of split, stacked, and stored firewood fuel. A cord of wood has a volume of 128 cubic feet and generally consists of 600 to 800 logs.
Cords may be further divided into half cords, face cords, and full cords. You can learn more about these measurements in our firewood size guide.
Creosote
Like smoke, creosote is a byproduct of combustion. It’s caused by a poor draft, a cold flue, and incomplete combustion of wood fuel. A sticky, tar-like substance, creosote builds up on the inner walls of a chimney over time, hardening into a highly flammable material that blocks the flue.
You can learn more about what creosote is, how it forms, and how to prevent and get rid of it in our guide to creosote.
Downdraft
A downdraft occurs when flue gasses flow downward in the chimney flue rather than drafting upward and out of the chimney. Downdrafts are caused by damaged chimneys, poorly built chimneys, and temperature and pressure differences inside and outside of the chimney.
Draft
In a chimney, draft is the upward flow of air caused by the pressure differences inside and outside the flue. Draft is affected by the height of the chimney, the width of the flue, inside and outside temperatures, and more factors.
Keeping the static pressure inside the chimney as low as possible helps to maintain a good draft.
Efficiency
A wood heating appliance’s efficiency is the percentage of the heat energy in its fuel load that is actually delivered to the area meant to be heated. For instance, if a wood stove’s fuel load contains 100,000 BTUs and 78,000 of those BTUs are delivered into the home as heat, that stove’s efficiency rating is 78%.
EPA
The Environmental Protection Agency, or EPA, is the government agency charged with (among other things) regulating the number of particulates produced by wood heating appliances.
Wood heating appliance manufacturers must ensure that their appliances meet the agency’s emission standards.
Firebox
The firebox is the heart of a wood stove or furnace. It’s the compartment in which the wood fuel is burnt. Heat energy is drawn from the firebox and delivered throughout the home as radiant heat (in a wood stove or pellet stove) or as forced-air heat (in a wood burning furnace).
Firebrick
Firebrick is a refractory product that lines the fireboxes of many wood heating appliances. Its purpose is twofold:
- It protects the interior of the appliance from heat damage
- It absorbs and radiates heat to facilitate more efficient heat delivery
You can learn more about different types of firebricks in our firebrick comparison.
Flue
A chimney’s flue is the passageway through which the smoke and other gasses travel to be vented out of the home. The chimney is a structure that contains the flue, while the flue itself is the actual pipe through which the combustion gasses move.
In a masonry chimney, a flue is a round or square-shaped clay pipe. In other chimney systems, the flue may be made from Class A chimney pipe.
Hardwood
Hardwood is a generalized category of several wood species. Hardwoods come from the wood of deciduous trees (i.e., trees whose seeds contain a hard outer shell). Because they put out less smoke and relatively more heat energy, hardwoods are ideal for use in wood heating appliances.
Pellet Stove
Pellet stoves are a type of wood heating appliance that utilize wood pellets as their fuel source. Their comparatively low heat output makes them best suited to small- and medium-sized homes. Our guide to the best pellet stoves on the market covers some of the top-rated models.
Seasoning
Seasoning is the process by which freshly cut cordwood is left to cure outdoors for 6 to 12 months to lower its moisture content. Burning unseasoned firewood can result in creosote buildup. That’s why it’s vital to season your firewood before burning it in your heating appliance.
Secondary Combustion
Also known as gasification, secondary combustion occurs when smoke and other gaseous combustion byproducts are burned away before being vented out of a wood heating appliance’s flue. This process results in fewer emissions and more delivered heat.
Many modern wood stoves and furnaces are designed to facilitate secondary combustion as it helps increase efficiency and decrease the creation of particulates.
Softwood
Softwood is a generalized category of several wood species. Softwoods come from the wood of coniferous trees (i.e., trees whose seeds do not contain a hard outer shell). Because they produce more smoke and burn quickly, softwoods are ideal for fire pits and campfires rather than wood stoves or furnaces.
Spark Arrestor
A spark arrestor is typically situated on top of a chimney flue. Consisting of metal mesh (often as part of a chimney cap), a spark arrestor’s job is to intercept any stray sparks or embers that may have wafted up the chimney flue (as these sparks can float away and unintentionally start fires outside of the home).
Static Pressure
Static pressure is a measurement of airflow resistance in a chimney flue. The higher the static pressure, the harder it is for flue gasses to travel up the flue to be vented out of the home. If the static pressure in a flue is too high, a downdraft will occur.
Water Column Inches
Water column inches (WIC) are the units used to measure static pressure. They’re defined as the amount of pressure exerted by a column of water that is a specific number of inches high (e.g., 2 water column inches represents the weight of a column of water that is 2 inches high and 1 inch wide).
Wood Furnace
Wood furnaces are a type of wood heating appliance. They utilize cordwood fuel. A central, forced-air heating unit, a wood furnace connects to a home’s ductwork and relies on a distribution blower to blow heat created in the firebox into the rest of the home.
Our guide to the best wood furnaces compares several of today’s top models.
Wood Pellets
Wood pellets are a type of fuel used in wood heating. They consist of pressed sawdust and other wood waste products. Used in pellet stoves and pellet fire pits, their low moisture content means wood pellets burn very cleanly and produce very little creosote.
Wood Stove
A wood stove is a type of wood heating appliance. Unlike a wood furnace, which relies on a distribution blower to circulate warm air through a home’s ductwork, a wood stove relies solely on radiant heat to warm a home (though some models do include a fan that blows warm air throughout the room in which the unit is installed).
Our guide to the best wood stoves of the year compares some of the market’s top-selling units.
How Do You Get Started with Wood Heating?
Now that you’re more familiar with some of the most commonly used terms in the world of wood heating, where do you go from here? What’s the best way to start heating your home with wood?
One of the best places to start is by finding the right kind of wood heating appliance for your home. Our comparison between wood stoves and wood furnaces, for example, pits both of those appliances against each other to help you discover which one is best suited for you.
