A tankless, or on demand, water heater heats water as it flows through the unit rather than storing a tank of hot water. They take up less space and can last longer than a conventional tank, but they trade one maintenance job (replacing the anode rod) for another: regular descaling. Hard water minerals build up inside the heat exchanger over time, and without periodic flushing that buildup quietly cuts efficiency and shortens the unit's life.
$150 to $300 a year for professional descaling, $3,900 to $6,500 to replace or install a unitAddress soonPlumbingHeating
The quick answer
A tankless water heater saves space and gives endless hot water, but it isn't maintenance-free: in hard-water areas it needs regular descaling or the heat exchanger scales up and efficiency drops. Budget $150 to $300 a year for professional descaling, $3,900 to $6,500 to replace or install a unit. Ask for service records and have the venting checked, older installs with improper plastic venting are a known safety issue. No maintenance history on an older unit is a fair negotiation point.
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Why it matters
In hard water regions, and much of Alberta, Saskatchewan, Manitoba, and parts of Ontario qualify, skipping descaling can cut a unit's working life roughly in half and push energy use up meaningfully as the heat exchanger scales over. On the gas side, older tankless installations sometimes used plastic venting that wasn't rated for the job. Ontario's technical safety regulator flagged unmarked ABS and PVC gas venting for cracking and melting risk, which is why any gas fired unit needs venting material certified to the current standard, not whatever plastic pipe happened to be on hand at install.
How to spot it
Ask when the unit was installed and whether it's been descaled annually, since this is a maintenance history question more than a visual one. Look at the gas venting where it exits the unit and the wall or roof. Certified venting is typically marked along its length; unmarked, unbranded plastic pipe is the flag. Check whether a scale filter was installed at the unit, a small inline cartridge that reduces how often descaling is needed. For electric units, hard water buildup is less of a fire or safety issue but still reduces efficiency and lifespan the same way.
What it costs
Professional descaling runs roughly $150 to $300 a year, or every six to nine months in harder water areas. A full unit replacement, including a gas line or electrical upgrade if needed, typically runs $3,900 to $6,500 installed.
What to do
Ask the seller or their agent for the maintenance and descaling history. If there's no record of descaling and the home is in a hard water area, budget for a flush soon after move in and factor a shorter remaining lifespan into your number. Have a licensed gas technician check the venting material on any gas fired unit.
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Common questions
How do I know if a tankless unit has been maintained?
You ask, because this is a maintenance history question rather than a visual one. Get the install date and whether it has been descaled annually. Descaling runs $150 to $300 a year and replacement $3,900 to $6,500, and skipping descaling in a hard water area can cut the unit's life roughly in half.
What is the venting concern?
Ontario's technical safety regulator flagged unmarked ABS and PVC gas venting for cracking and melting risk. Certified venting is marked along its length; unmarked, unbranded plastic pipe on a gas-fired unit is a flag for a licensed gas technician.
Is tankless better than a tank?
It takes less space and can last longer, but it trades one maintenance job for another, and the replacement cost is higher. It is a different set of tradeoffs, not a straight upgrade, and a neglected tankless unit can be worse value than a maintained tank.
Should a lack of descaling records change my offer?
It should change your expected remaining lifespan, which is the same thing. If there is no maintenance record and the home is in a hard water area, budget for a flush soon after move-in and shorten the clock you assume on the unit.
Descaling frequency and lifespan vary with local water hardness. Casaroo flags, it does not inspect. Confirm condition with a licensed plumber or gas technician.
Last reviewed 2026-07-09.
This guide is general education, not a home inspection and not advice for your specific property. Always
consult the appropriate licensed professional, and get a licensed home inspection before you remove conditions
or buy. Cost ranges are 2026 estimates that vary by region, size, and access; confirm specifics with a
qualified professional.