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The Sterling Chimney Sweep teamDoes a gas fireplace need a chimney liner?
It depends on the type of unit. A gas insert in an old masonry chimney usually needs a liner, while a direct-vent gas fireplace brings its own pipe. The maker's instructions and the state of your flue make the call. Gas exhaust is cooler than wood smoke and carries moisture, which is hard on old brick and tile.
Why does gas exhaust ask for a liner?
A wood fire is hot enough to carry smoke up a wide flue quickly. A gas fire sends out cooler exhaust with water vapor in it. In an old, oversized flue, that exhaust cools and condenses on the walls, which can break down mortar and tile over time. A liner sized to the unit keeps the exhaust moving and sealed off from the masonry.
Which type of gas fireplace do you have?
| Type | How it vents | Liner? |
|---|---|---|
| Gas insert in a masonry fireplace | Up the existing chimney | Usually yes, a sealed liner sized to the insert |
| Direct-vent gas fireplace | Its own pipe through a wall or the roof | No masonry flue involved |
| Gas logs in a wood-burning fireplace | Through the existing flue, damper fixed open | Depends on the flue's condition |
| Factory-built gas fireplace with a metal chimney | Through its own metal pipe | The pipe is the vent |
What about gas logs in a wood-burning fireplace?
Gas logs burn in the old fireplace, so they vent through the existing chimney. Vented gas logs need the damper held fully open, usually with a clamp, as the maker specifies, so exhaust cannot spill into the room. The flue itself must be sound, because all of that exhaust goes up it. A camera look checks the tile and the joints, and a sweep clears whatever buildup earlier wood fires left behind.
What you can check safely
- Find the make and model on the label inside the unit or in the manual.
- Look outside for a vent fitting on the wall, which usually means a direct-vent unit.
- Check whether the glass front or logs have soot or an unusual film.
Stop and call: if you smell gas, leave the house first, then call your gas utility, such as Xcel Energy or CenterPoint Energy, from outside. When a carbon monoxide alarm goes off, go outside first and then call 911.
How do you know what your flue needs?
A camera look inside the chimney shows the tile, any cracks and the size of the flue. After it, we can tell you whether your unit needs a liner or can use the existing flue as it is. Our chimney liner service covers the options. We look at gas flues in Stillwater, West St. Paul and across the east metro.
Gas liner questions
Short answers first.
How do I tell which gas fireplace I have?
Check the label and the manual first. A pipe or fitting on an outside wall usually means direct vent. A unit sitting inside a brick fireplace is often an insert.
Can a liner be added later?
Yes. A flexible stainless liner can go down an existing flue. We look first, so the liner matches your unit's outlet.
Is a liner the same as a vent pipe?
For a gas insert, the liner is the vent pipe inside the old chimney. For a direct-vent unit, the vent pipe replaces the chimney altogether.
Why is gas exhaust hard on an old chimney?
Cooler, damp exhaust can soften mortar and crack tile over time, and a wide flue lets it condense. A sealed liner protects the masonry.
Gas insert and an old chimney?
Tell us what the unit is and what the chimney looks like, and we will plan the first look.