Home / Glossary
Fireplace and wood stove terms, in plain English
The words you'll run into when you shop for a stove or fireplace, or read your local burn rules.
- BTU
- British thermal unit, the standard measure of heat. Stoves and fireplaces are rated in BTU per hour: the higher the number, the more heat. See it in action →
- Burn ban (no-burn day)
- A day when your local air agency bans burning wood because air quality is poor. Fines can apply. See it in action →
- Catalytic stove
- A wood stove with a catalytic combustor, a honeycomb part that helps burn off smoke at lower temperatures. The combustor wears out over time and needs replacing. See it in action →
- Chimney liner
- A metal or clay tube inside the chimney that carries smoke out safely. When you add a stove or insert to a masonry chimney, the liner is usually matched to the stove's flue collar size.
- Cordwood
- Ordinary split firewood, the logs most people burn. Some stoves are tested by the EPA on cordwood, which allows a slightly higher smoke limit (2.5 grams an hour) than the standard test. See it in action →
- Creosote
- A tar-like residue that builds up inside chimneys when wood smoke cools. Too much of it is a fire risk, which is why chimneys need regular sweeping.
- Crib wood
- Stacked, uniform lumber the EPA uses in its standard stove test, so every stove is tested the same way.
- Direct vent
- A gas fireplace that pulls in outside air and sends exhaust out through a pipe in the wall, sealed off from the room. See it in action →
- Draft
- The upward pull of air through a chimney that keeps smoke going out instead of into the room.
- Efficiency
- The share of the fuel's energy that ends up as heat in your home. On our stove pages we call it "heat from each log." See it in action →
- Emissions (smoke)
- The fine particles a stove gives off, measured by the EPA in grams per hour. Lower is cleaner. New wood stoves must stay at or under 2.0 grams an hour (2.5 on the cordwood test). See it in action →
- EPA-certified
- A stove that passed the EPA's smoke test and can legally be sold new in the U.S. See it in action →
- Firebox
- The part of the stove that holds the fire. A bigger firebox holds more wood, so a load burns longer. See it in action →
- Flue collar
- The round opening on top or back of a stove where the stovepipe connects. Its size decides your pipe and liner size.
- Hybrid stove
- A wood stove that combines a catalytic combustor with the secondary-burn design of non-catalytic stoves. See it in action →
- Insert
- A stove (wood, pellet, gas or electric) built to slide into an existing fireplace opening, turning it into a better heater. See it in action →
- kWh (kilowatt-hour)
- The unit your electric bill uses. A 1,500-watt electric fireplace on full heat uses 1.5 kWh every hour. See it in action →
- Non-catalytic stove
- A wood stove with no catalytic combustor. It burns off smoke with extra air fed into the firebox instead. See it in action →
- Pellet stove
- A stove that burns small compressed wood pellets, fed automatically from a hopper by an electric motor. See it in action →
- Therm
- The unit many gas bills use. One therm is 100,000 BTU. See it in action →
- Vent-free (ventless)
- A gas fireplace or log set that has no vent to the outside. Some places restrict or ban them, so check local rules.
- Zero-clearance fireplace
- A factory-built fireplace designed to sit close to wood framing, so it can be built into a wall without a masonry chimney.