Beecher furnace swap left the water heater venting alone: why the old flue could not do the job
A Beecher homeowner put in a high-efficiency furnace and got a lower gas bill. What nobody checked was the old masonry flue, now venting the water heater by itself.
The furnace moved out and the flue got too big
When a high-efficiency furnace goes in, it usually vents sideways through PVC and no longer uses the chimney. That is good for the furnace. The problem is the water heater that used to share the masonry flue. On its own, a single appliance puts out a fraction of the heat the pair once did, and that masonry channel is suddenly far larger than it needs to be.
In an older Beecher home with a tall exterior chimney, the flue stays cold. Water heater exhaust is cool and wet to begin with, and in an oversized cold flue it slows down, cools further, and never builds the draft it needs to climb. We see the evidence at the base: rust on the draft hood, white mineral staining on the brick, and a damp cleanout.
What we actually look for
A Level 1 inspection here is not a flashlight glance. We check that the water heater is drafting under real conditions, with the exhaust fan and dryer running the way the house runs on a cold morning. We look for spillage at the draft hood, corrosion inside the flue, and loose or missing tiles that let exhaust leak into the chase instead of leaving the roof.
Beecher sits out on open prairie, and that steady wind can push down a cold, oversized flue hard enough to stall a lone water heater. A backdrafting water heater is a carbon monoxide concern, which is exactly why this gets looked at rather than left alone.
The fix is usually a right-sized liner
The standard answer is to line the flue down to the size one appliance actually needs. A correctly sized liner warms up fast, holds its draft, and keeps the acidic condensate off the old brick. We work to the NFPA 211 standard on sizing, and the liners we install are listed to UL 1777.
If you have upgraded a furnace in the last few years and never had the chimney looked at, that is the time to do it. We can tell you quickly whether the flue is still doing its job. Pricing for inspections is published on our pricing page.
If this sounds like your house: we handle chimney inspection across Kankakee County, and our Beecher page covers what we usually find there. Call (815) 449-4264, 7am to 9pm, any day.
Quick questions
Why would a new furnace cause a chimney problem?
The furnace was doing most of the venting work. Remove it and the water heater is left in a flue built for two appliances, so it is oversized, stays cold, and can struggle to draft.
Is a backdrafting water heater dangerous?
It can be. Exhaust that spills back into the room instead of up the flue carries carbon monoxide, so it is worth confirming the appliance drafts correctly under normal household conditions.
How do I know if my flue is too big now?
An inspection tells you. Signs we look for are rust on the draft hood, white staining on the brick, a damp cleanout, and exhaust spilling when the house is running fans.
Do you fix it the same visit?
Not usually. We confirm the problem first, then schedule a right-sized liner. We are open seven days a week, 7am to 9pm, if you want to get on the calendar.
Published October 20, 2026 · By Jacob Dove, Friendship Chimney Sweep, Bourbonnais IL