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, 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.
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.
Education and triage, not a home inspection. Casaroo flags unit age and vent material from your photos where visible. A licensed plumber or gas technician confirms condition and maintenance history. We flag; we don't inspect.
Common questions
What is Tankless water heaters: maintenance and venting?
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.
Why does it matter for home buyers?
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 can I 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.
How much does it cost to fix?
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.
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.