Why might I need a chimney liner?
If you live in an older home (30 years or older), the chimney on your house has probably worked just fine for years and you may wonder why you’d suddenly need a flue liner when you replace your furnace.
Most older flues are masonry, either brick or clay, and were sized and designed for furnaces and water heaters that were anywhere from 45-65% efficient. Because of the low efficiency of the furnace, high volume and high-temperature flue gases from the equipment kept the flue warm and dry.
A lot of mid-efficiency 80% AFUE furnaces generally have lower volume and lower temperature exhaust. Many are still vented into existing flues and, because of the lower temperature, the acidic moisture from the flue gas can condense out and collect on the porous masonry, eating it away. High-efficiency 90+% AFUE condensing furnaces are usually vented separately to the outside using PVC (vs. through an existing chimney) and tend to leave the water heater venting alone into the flue. Water heaters have very low volume and low-temperature flue gas and, like mid-efficiency furnaces, the same masonry damage can happen.
Installing a flexible liner is the best way to protect your existing masonry or clay chimney by providing a barrier from the flue gases and moisture. Older chimneys can often have cracks and flue liners help eliminate the danger of preventing leaking gases.