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A high-efficiency gas furnace had been vented into the home’s original brick chimney for over a decade — and it was destroying the masonry from the inside out. We installed a properly sized insulated stainless liner before the damage spread further.
The homeowner called us during their annual chimney cleaning — they’d noticed white powdery residue on the brick face of their chimney outside, and a faint musty smell in their basement that seemed to get worse in winter. They wanted to know if it was anything to worry about.
When we got there, it was something to worry about. This was a 1908 Victorian near Woburn Center, originally built with a chimney designed to vent a coal-burning furnace. At some point in the 1990s, that furnace had been replaced with a modern high-efficiency gas unit — and the new appliance had been vented straight into the original chimney without a proper liner.
The problem with that setup: high-efficiency gas appliances produce acidic condensate that attacks unlined brick and clay tile from within. After ten or fifteen years of this, you start to see exactly what we were seeing on this house. The white residue outside was efflorescence — minerals being leached out of the brick by moisture. The musty smell was the masonry slowly absorbing condensate and not drying fast enough between cycles. Inside the flue, our camera showed significant deterioration of the clay tiles, with chunks missing at the joints.
The fix here was straightforward in concept and important to do right: install a stainless steel liner sized specifically for the furnace it would serve, and insulate it properly so the flue gases stay hot enough to vent without condensing inside the masonry.
We sized the liner to the BTU output of the existing furnace — undersized liners don’t draft properly, oversized liners cool too fast and recreate the same condensate problem. The liner itself was 316Ti stainless steel, the grade rated for gas appliances and corrosive condensates. We wrapped it in proper ceramic insulation before feeding it down the chimney, sealed both ends correctly, and added an appropriate cap rated for the appliance type.
We also did a full camera inspection of the existing masonry before and after the liner installation. The damage was significant but contained — no immediate structural concerns, no need for a rebuild. With the liner in place, the masonry will stop deteriorating and slowly dry out over the coming year. We’ll do a follow-up inspection at the one-year mark to confirm.
The new liner is doing exactly what it should — keeping flue gases contained, properly venting the furnace, and protecting the masonry from any further deterioration. The musty smell in the basement was gone within a couple of weeks. The homeowner has documentation of the work for their home file, manufacturer warranties on the liner and insulation, and a five-year workmanship warranty from us.
If your older home has a modern furnace venting into an unlined chimney, this is something worth addressing before the damage gets serious. Learn more about our liner installation work or see other projects in Woburn homes.
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Many older masonry chimneys have unlined flues or clay tiles that have cracked over time. A stainless steel liner creates a safe, correctly sized, continuous flue that vents your appliance properly and protects the surrounding masonry from heat and acidic gases.
Yes. Stainless liners are ideal for historic homes because they restore safe venting without changing the chimney's exterior appearance - preserving the home's character while bringing the flue up to modern safety standards.
A quality stainless steel liner is built to last for decades and typically carries a long manufacturer warranty, making it a durable, long-term solution rather than a repeated patch repair.
Yes. A properly sized liner vents combustion byproducts safely, reduces creosote accumulation, shields the masonry from heat, and helps your fireplace or appliance run more efficiently.
Always. We match the liner diameter to your fireplace or appliance and flue so it drafts correctly and meets code - an incorrectly sized flue can cause drafting and safety problems.
