Strike a match in your fireplace and the smoke goes up the chimney instead of into your living room. It seems automatic, but a lot of physics is doing quiet work behind that simple fact. Understanding how your chimney draws — what professionals call draft — helps Romeoville homeowners recognize why a fireplace sometimes smokes, and what to do about it.
Why smoke goes up: draft and the stack effect
Draft is the upward flow of gases through the flue, and it runs on a simple principle: hot air rises. When you burn a fire, the combustion gases are far hotter and lighter than the surrounding air, so they climb the chimney. That rising column does two things at once — it carries smoke out of the house and it pulls fresh air into the fire to keep it burning. The taller and warmer the flue, the stronger the pull. Your whole house plays a part too, through the stack effect: warm indoor air naturally rises and seeks to escape up high, and the chimney is the tallest, easiest exit it has.
What goes wrong when a fireplace smokes
When smoke rolls into the room, the draft has failed somewhere. The most common reasons are a cold flue that was never primed, so the air column is too heavy to rise; a flue narrowed by heavy creosote or blocked by debris; a house so airtight that the fire cannot get the makeup air it needs; or a flue poorly matched in size to the fireplace. Weather plays in as well — warm days weaken the temperature difference that drives draft, and wind or a depressurized house can push air back down the flue.
Getting a strong, clean draft
Several of these fixes are simple. Prime a cold flue by holding a rolled-up, lit newspaper near the open damper for a minute before lighting the fire, so the air column warms and starts to rise. Crack a nearby window in a tight house to supply makeup air. And keep the flue at full diameter with regular chimney sweeping, since creosote buildup steadily chokes the draft. When smoking persists despite those steps, a chimney inspection can find a sizing problem, a partial blockage, or a structural issue that needs correcting.
A fireplace that smokes is not something you have to tolerate — it is telling you the draft needs attention. Call Indigo Chimney Sweep at (815) 296-9565 or book online. We are bonded and insured, and we tell you the price up front. We will diagnose why your Romeoville fireplace is not drawing and get the smoke going where it belongs.
Frequently asked questions
What is chimney draft?
Draft is the upward flow of air and combustion gases through the flue. Hot gas from the fire is lighter than the cooler air around it, so it rises, and that rising column pulls fresh air into the fire and carries smoke out of the house. Good draft is what makes a fireplace work.
What is the stack effect?
The stack effect is the natural tendency of warm air to rise inside a building and escape through openings up high, drawing replacement air in down low. A chimney is a tall vertical shaft, so it participates strongly in this effect — which is what gets the draft started and keeps it going.
Why does my fireplace smoke into the room?
Smoke in the room means the draft is too weak or reversed. Common causes are a cold flue that has not been primed, a blockage or heavy creosote narrowing the flue, a house that is too airtight to supply makeup air, or an undersized or oversized flue for the fireplace. Each has a specific remedy.
How do I prime a cold flue?
Warm the flue before lighting the main fire. Rolling up newspaper into a torch and holding the lit end up near the open damper for a minute or two warms the air column so it begins to rise. Once the flue is warm, the fire lights and draws far more cleanly.
Can a house be too tight for a fireplace to draft?
Yes. A well-sealed modern home can starve a fireplace of the makeup air it needs, so the draft weakens or reverses and smoke spills in. Cracking a nearby window slightly, or providing a dedicated air supply, often restores the draft in a tight house.
Does flue size affect draft?
Very much. A flue that is too large for the fireplace lets gases cool and slow before they exit, while one that is too small cannot carry the volume of smoke produced. Matching the flue to the appliance is part of why proper sizing matters when relining or installing an insert.
How does creosote hurt draft?
Creosote narrows the flue. As buildup thickens, the passage for smoke and gases shrinks, the draft weakens, and more smoke lingers and spills into the room. Regular sweeping keeps the flue at full diameter so the draft stays strong — another reason cleaning is about performance, not just fire safety.
Can weather change my draft?
It can. Warm outdoor temperatures reduce the difference that drives the draft, wind can push against the flue, and a strongly depressurized house can reverse the flow. Persistent draft trouble that changes with the weather is worth an inspection to find the underlying cause.
Written by Jamie Reed, operations manager at Indigo Chimney Sweep.
Published September 17, 2026