Chimneys built before roughly 1930 were frequently constructed with no flue liner, meaning combustion gases pass directly against brick and mortar. In Aurora’s historic districts this is common, and it is a genuine safety matter rather than a cosmetic one.
Why old chimneys were built this way
Flue liners were not standard practice in American residential construction until the early twentieth century, and enforcement lagged well behind that. A great many of Aurora’s late-1800s and early-1900s homes, particularly in the historic districts near downtown and along the river, were built with bare masonry flues.
At the time this was normal. The problem is that a century of heating has taken its toll: mortar joints inside the flue erode, gaps open between bricks, and the passage that was already imperfect becomes genuinely leaky.
What actually goes wrong
Two risks matter. The first is heat transfer: without a liner, the flue wall may be a single brick thickness from framing, and sustained heat can pyrolyse nearby wood, lowering its ignition temperature over years until it can catch at surprisingly low heat.
The second is combustion gases. Gaps in an unlined flue allow carbon monoxide to migrate into wall cavities and living space rather than exiting at the top. Carbon monoxide has no smell, which is exactly what makes it dangerous, and it is the reason a working CO alarm is non-negotiable in an older home.
How you find out, and what the fix is
You cannot determine this from the firebox. It requires a camera scan of the full flue length, which is what a Level 2 chimney inspection provides. We record the footage so you can see the condition rather than take our word for it.
If the flue is unlined or the existing liner has failed, the standard remedy is a stainless steel liner sized to the appliance and insulated where required, installed inside the original masonry. It restores a continuous, correctly sized path without altering the exterior of a historic chimney. We do not quote relining without seeing the flue first, because size, height, and appliance type all change the specification substantially.
Talk to a local chimney pro
If you own an older home in Aurora and do not know whether your chimney is lined, that is worth resolving before you light the first fire of the season.
Written by Josh Amber, co-owner of Ember Chimney Sweepers, Oswego IL. Published September 21, 2026.