Heat exchanger inspection: how often, and what to look at

Three gas-fired appliances in the same building can carry the same part — a wall separating combustion gases from the air people breathe — and share no inspection calendar whatsoever. The steam boiler in the basement falls under a regulation that schedules periodic inspections. The rooftop unit over the gym answers only to its installation manual. The hot water boiler next door could go either way, depending on its operating pressure. That is where heat exchanger inspection actually gets decided in Quebec: not in the method, which is well documented, but in knowing which of your appliances has nobody scheduling it.

A heat exchanger is the only component whose failure changes what is in the air of an occupied space. A failed burner stops the heat; a breached exchanger keeps heating and adds combustion products to the supply. That asymmetry is why its inspection deserves a date on a calendar rather than a line item among thirty on a service sheet.

What you need on hand

• Inspection camera with a small-diameter articulating probe and adjustable lighting.
• Calibrated combustion analyzer, O₂ and CO cells in good condition.
• A separate ambient CO monitor worn on the person, not the analyzer.
• Inspection mirror, a strong light and a non-metallic brush to clear soot before looking at anything.
• A camera or phone: every questionable area gets photographed with something for scale.
• The manufacturer’s manual for that appliance, not a generic one.

⚠ Safety: three conditions before a panel comes off

Gas closed and electrical supply locked out before any panel is removed. The appliance must be cold — a combustion chamber surface stays hot long after the burner stops, and a steam boiler holds pressure well after shutdown. And a boiler room is not an ordinary space: if the inspection means entering a boiler shell, the confined space procedure applies in full, with an attendant and atmospheric testing.

How often does a heat exchanger inspection have to happen?

There is no single answer, and that is exactly what creates the blind spots. Two regimes coexist in Quebec. Appliances covered by the Pressure Equipment Regulation get periodic external and internal inspections, at intervals the regulation sets by equipment type, performed by a person recognized by the RBQ. Every other gas appliance has no regulatory calendar at all — only the manufacturer’s manual and the general duty to keep a compliant installation in good order.

The practical consequence runs against intuition. The best-watched appliances are the ones whose risk is already well framed; the forgotten ones are frequently the gas-fired rooftop units — which blow straight into occupied space. In a Montreal-area portfolio that typically holds more rooftops than boilers, the blind spot is on the roof.

Step 1 — Read the file before opening the appliance

An inspection starts in the binder. Three data sets steer everything after: the history of combustion analyses, the volume of make-up water added to the loop, and the lockouts logged since last season. A loop that keeps drinking make-up water eventually pays for that mineral content somewhere. A slow year-over-year drift in CO, even below any threshold, says a surface is changing shape.

Step 2 — The external inspection, appliance cold

Before any panel comes off: rust staining and leak tracks underneath, bulging or distorted panels, condensation or beading at the vent connection, unusual play at the mounts. On a condensing appliance, the condensate pan and trap report directly on what is happening inside — condensate carrying black particulate points to combustion dirtying a surface you cannot see yet.

Step 3 — The fire side, and what soot tells you

The face exposed to the flame says the most. Clear the soot with the brush first, otherwise you are inspecting a deposit rather than metal. Then look for three things: flaking, which means corrosion in progress; distortion, which means local overheating; and cracking, which gets confirmed rather than assumed. A borescope inspection reaches the flue passages without disassembly, provided each questionable area is photographed with a reference so next year’s image can be compared. If a serious indication appears, the cracked heat exchanger decision tree takes over — a periodic inspection does not settle that question on its own.

Step 4 — The water side, or the air side

On a hydronic or steam appliance, the question is scale and sludge. A mineral layer on the exchange surface insulates the metal from the fluid meant to cool it, and the resulting hot spot is a rupture mechanism, not merely an efficiency loss. On a forced-air appliance, the equivalent question is airflow: clogged filters, a fouled blower wheel, dampers closed by an occupant. A unit that still heats adequately on reduced airflow is slowly cooking its own exchanger.

Step 5 — The running test

The inspection is not over when the panels go back on. Restart, let the appliance reach steady state, and log two things: ambient CO at breathing height in the space, and a full combustion analysis. Those values get compared against the previous inspection — the comparison, not the isolated reading, is what exposes an exchange surface that has started to move. For reference, Quebec’s occupational health and safety regulation sets a time-weighted average exposure value of 35 ppm over eight hours for carbon monoxide. In the supply air of a heating appliance, the only acceptable value is still zero.

From the field: a steam boiler and six compliant years

Institutional building in Longueuil, steam boiler feeding radiators and two ventilation coils. The file was spotless: periodic inspection certificates current, nothing outstanding. The call was about something else entirely — gas consumption climbing season over season with no change in occupancy.

The water-side inspection found a heavily scaled exchange surface, consistent with the history. The steam loop was losing water through failed traps, and the make-up water added every week brought its minerals with it. The certificates were all there; nobody had connected the make-up water volume to the condition of the exchanger. A regulatory inspection addresses the integrity of pressure equipment — it does not rule on efficiency, and it does not trace a cause upstream.

The fix ran in two stages: repair the traps to stop the water loss, then descale the exchanger. Consumption came back down, and one line was added to the monthly log — make-up water volume. It is the single measurement that warns of scaling before it costs an exchanger.

Set the date before the first -15 °C night

The useful move this week is not technical, it is clerical. List every combustion appliance in the portfolio and, next to each, two columns: which inspection regime applies, and the date someone last looked inside the exchanger. The rows with an empty second column are your fall work list, and nearly all of them will be rooftop units.

For an owner or property manager, that list is worth more than one more service contract: it converts a recurring expense into a defensible schedule, with appliances ranked by risk instead of by the order in which they broke down. It is the basis on which Montréal Combustion plans boiler service across a portfolio — starting with the appliances nobody had written down anywhere.