Do I need a new chimney liner with a high-efficiency furnace?

Yes, you typically need a new chimney liner when upgrading to a high-efficiency furnace. High-efficiency furnaces (90%+ AFUE) produce cooler, more acidic exhaust that can damage existing clay or metal liners not designed for condensing appliances.

High-efficiency furnaces create condensation as part of their operation, which makes the exhaust more acidic than traditional furnaces. This acidic moisture can deteriorate clay tile liners and cause corrosion in metal chimneys. Additionally, the cooler exhaust temperatures mean less natural draft, which can lead to poor venting and potential carbon monoxide issues if you use an oversized or inappropriate liner.

Most high-efficiency furnaces use PVC or ABS plastic venting that exits through a sidewall rather than up the chimney. This is actually preferred because it's designed specifically for the cooler, acidic exhaust these units produce. However, if you must vent through the existing chimney, you'll need a properly sized stainless steel liner rated for condensing appliances.

In Ottawa, TSSA regulations require proper venting for all gas appliances. Your licensed HVAC contractor will need to follow Ontario Building Code requirements and obtain the necessary TSSA permit for the installation. The venting method must match the furnace manufacturer's specifications - using an inappropriate liner or venting system violates code and creates serious safety risks.

Never attempt to connect a high-efficiency furnace to an existing chimney without professional assessment. The sizing, materials, and installation must be done by a licensed G2 technician who can ensure proper draft and safe operation. Carbon monoxide poisoning is a real risk with improper venting.

For a proper assessment of your specific chimney and venting needs, request a consultation with Ottawa HVAC Pro's licensed technicians who can ensure your installation meets all TSSA requirements.