Fireplace Insert Installation in St. Marys

A traditional masonry fireplace flue is sized for an open fire drawing a large volume of air, which is many times larger than what a sealed insert's combustion process actually needs. Connecting an insert to that oversized flue without a properly sized liner causes the exhaust gases to cool too much before reaching the top, leading to condensation, poor draft, and creosote buildup that accumulates faster than a normal wood-burning system would produce.

The fix is running a new liner, sized specifically to the insert's flue outlet, from the appliance connection point to the top of the chimney. For gas inserts this is typically a flexible stainless liner; for wood inserts it is usually an insulated rigid or flexible stainless liner rated for solid-fuel temperatures. Either way, the liner is what makes the whole system perform at its rated efficiency rather than well below it.

This is the step most often skipped or done poorly on cut-price insert installations, because it adds real material and labour cost that is invisible once the insert and surround are in place. It is also the step that most affects long-term performance and safety, which is why we treat it as non-negotiable regardless of budget pressure.

Before selecting a model, we measure the existing masonry opening's depth, width, height and the flue's internal dimensions, since insert models vary considerably in their footprint and not every unit fits every fireplace. A firebox that looks like standard size to the eye can be a few centimetres off from what a particular insert requires, which rules that model out regardless of how well it suits your heating goals otherwise.

We also check the condition of the existing masonry firebox itself during this step, since an insert installed into a deteriorated firebox is still sitting against damaged material even though it is no longer directly visible. Where the firebox shows significant deterioration, that repair typically needs to happen before or alongside the insert installation rather than being covered up by it.

Where the existing masonry opening is slightly undersized or irregularly shaped for the insert a homeowner has their heart set on, we will say so before ordering rather than after, since minor masonry modification to widen an opening is sometimes possible but adds cost and time that is worth knowing about upfront rather than discovering mid-installation.

Gas inserts are the most popular retrofit choice because they combine strong heat output with the convenience of a switch or remote start, and they need a liner but no chimney sweeping in the traditional sense once installed. Wood inserts retain the traditional burning experience while dramatically improving heat delivery over an open fireplace, though they still need annual sweeping like any solid-fuel appliance.

Electric inserts need no liner or venting at all, making them the simplest and least invasive installation, though they provide supplemental and ambiance heat rather than the higher output of gas or wood options. The choice generally comes down to whether you want a heating appliance you use regularly through winter or an ambiance feature used occasionally, since that changes which fuel type makes the most practical sense for your household.

Most gas and wood inserts offer an optional or built-in blower that pulls room air across the firebox and pushes it back out warmed, which meaningfully increases how far the insert's heat actually travels into the room rather than radiating only immediately in front of the opening. For larger or more open-concept rooms, this option is worth the modest additional cost in nearly every case we see.

Blower noise and speed control vary by manufacturer, and some higher-end models offer variable speed control paired with a thermostat so the blower ramps up and down automatically rather than running at a single fixed speed regardless of how warm the room already is. We walk through these options relative to your room size and usage pattern before you commit to a specific model.

It is worth noting that a blower is an electrical component, and its failure does not affect the insert's core heating or combustion safety, only the distribution of the heat produced, which is a useful distinction if a blower motor ever needs replacing down the line.

Sealed inserts are particularly valuable in Ontario's climate because an open fireplace's constant draft loss works directly against a furnace trying to heat the same house through a long winter. Homeowners who switch from an open fireplace to a sealed insert often notice a genuine difference in how warm the room stays and how much less the furnace runs during evening fireplace use.

A correctly insulated liner also matters more here than in milder climates, since flue gas that cools too quickly in cold outdoor conditions condenses faster, and Ontario winters provide plenty of very cold nights for that to happen if the liner is undersized or uninsulated.

Liner sizing for insert installations follows manufacturer specifications and applicable CSA and WETT-referenced installation standards, and gas insert connections must be completed by a licensed gas technician under Ontario's gas safety framework. These are not optional refinements — an incorrectly sized or uninsulated liner is a recognized cause of chimney fires and carbon monoxide issues, which is why it sits at the centre of any insert inspection.

Clearances between the insert, its surround panels, and any combustible mantel or trim above the opening also need to be verified against the specific appliance's listing, since inserts vary in how much heat they radiate forward compared to the original open fireplace.

Where an insert is already installed but underperforming, the fault often traces back to an undersized or damaged liner rather than the appliance itself, and correcting the liner alone can restore expected performance without replacing the whole unit. We check liner condition with a camera inspection before assuming the insert itself needs replacement.

Genuine appliance replacement becomes the right call when the insert's heat exchanger, burner assembly, or firebox has failed beyond economical repair, or when a homeowner wants to change fuel type entirely, since converting fuel type generally means a new appliance and reworked venting rather than a partial swap.

A properly installed insert with a documented, correctly sized liner is viewed favourably by both buyers and insurers, since it demonstrates the fireplace was upgraded to current safety and performance standards rather than left as an aging open masonry system. Undocumented or improperly linered inserts, by contrast, are a common finding in pre-purchase inspections and can raise questions about past workmanship.

Keeping the installation paperwork, including liner specifications and appliance model information, gives future buyers or your insurer a clear record of what was done and to what standard, which is worth far more at resale time than the marginal cost saved by skipping proper documentation initially.