Limestone chimney relined for a new high-efficiency furnace: matching the liner to the appliance
A new furnace is sized to the house. The flue venting it has to be sized to the appliance, and in Limestone an old masonry chimney was far too big for the mid-efficiency unit now using it.
A flue that is too big is its own problem
People assume a bigger flue is a safer flue. With combustion appliances the opposite is true. A furnace needs its exhaust to move fast enough to clear before it cools. In an oversized masonry flue the exhaust slows, cools, and condenses, and that condensate is acidic. It eats mortar joints and clay tile from the inside, and it keeps the flue from drafting cleanly.
This Limestone home had a tall old chimney built for a coal or oil setup decades ago. The new furnace was a fraction of that capacity, so the flue was cavernous by comparison. The tile had already started to flake where the acidic moisture had been working on it.
Sizing the liner to the appliance
Relining is how you fix a mismatch like this. We size a stainless liner to what the furnace’s exhaust actually needs, run it the full height, and insulate it so it warms quickly and stays warm. A right-sized, insulated liner holds its draft, keeps the condensate from ever touching the old brick, and gives the appliance a clean, predictable path out.
We size to the NFPA 211 standard, and the liners we install are listed to UL 1777. That listing is not decoration. It means the liner has been tested for the service it is doing, which matters when it is carrying combustion gas day in and day out all winter.
When to think about it
The right time to look at the flue is when you change the appliance, not years later when a stain shows up on the ceiling or the furnace starts short-cycling. If you have put in a new furnace or boiler and the installer did not touch the chimney, that is worth a second look.
We have been relining chimneys across Kankakee County for 29 years and can tell you quickly whether yours is sized right for what is venting through it. We are open seven days a week, 7am to 9pm. Pricing for relining is published on our pricing page.
If this sounds like your house: we handle chimney relining across Kankakee County, and our Limestone page covers what we usually find there. Call (815) 449-4264, 7am to 9pm, any day.
Quick questions
Can a chimney be too big for a furnace?
Yes. An oversized flue lets exhaust slow and cool, which causes acidic condensation that damages the masonry and weakens draft. The flue should match the appliance, not just be large.
What does UL 1777 mean on a liner?
It means the liner has been tested and listed for venting that service. It is the standard we hold our relining work to, alongside the NFPA 211 sizing guidance.
Do I need a new liner just because I changed furnaces?
Not always, but it should be checked. A new, smaller appliance often leaves the old flue oversized, which is exactly the mismatch that calls for a right-sized liner.
How long does relining take?
Most residential relines are a one-day job once we have confirmed the sizing and the condition of the chimney. We go over the scope with you before we start.
Published October 24, 2026 · By Jacob Dove, Friendship Chimney Sweep, Bourbonnais IL