Scale is a hard mineral deposit, mainly calcium carbonate, that forms inside water heating equipment when dissolved minerals in the water precipitate out as it's heated.
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Scale is the crusty, chalky mineral buildup, primarily calcium carbonate, that forms inside water heaters, boilers, and tankless heat exchangers as hard water is heated. Heating water reduces its ability to hold dissolved minerals in solution, so those minerals precipitate out and cling to hot surfaces inside the appliance. Over time, scale acts as an insulating layer, making the appliance work harder to transfer heat, which can reduce efficiency and, in tankless units especially, restrict flow through narrow passages.
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Water naturally contains dissolved minerals, mainly calcium and magnesium, picked up as it travels through soil and rock before reaching a home's supply. Water with a higher mineral concentration is described as 'hard,' while water with lower mineral content is 'soft.' When hard water is heated, its capacity to hold those minerals dissolved decreases, and the excess mineral content comes out of solution as solid scale, clinging most heavily to the hottest surfaces inside the appliance, exactly where efficient heat transfer matters most.
This is a purely chemical process tied to water hardness and temperature, not a sign of a defective appliance. Any gas water heater, boiler, or tankless unit heating hard water will accumulate scale over time; the only variables are how much and how fast.
Much of Metro Vancouver, including Vancouver proper and areas served by the region's reservoir system, has notably soft water, which means scale tends to accumulate more slowly here than in many other parts of the country. Homes on well water, more common in parts of the Fraser Valley, often deal with considerably harder water and correspondingly faster scale buildup, which can mean different maintenance intervals matter more in those areas.
This regional difference is worth knowing because generic scale-prevention advice written for a harder-water region elsewhere may not apply the same way to a typical Metro Vancouver home on municipal reservoir water, though it's still a real consideration, not a non-issue.
In a storage tank water heater, scale settles at the bottom near the burner or heating surface, insulating the water from the heat source and reducing recovery rate over time. In a tankless water heater, scale is a bigger concern because water passes through a compact heat exchanger with narrow internal passages, and scale buildup there can restrict flow and reduce heat transfer efficiency more noticeably than in a large storage tank. This is part of why tankless manufacturers often recommend periodic descaling flushes, particularly in harder water areas.
Boilers can develop scale in their heat exchangers too, especially where fresh makeup water is frequently introduced to a hydronic loop rather than the same closed water recirculating for years.
Safety note
Any work on the gas piping, burner, venting, or pressure components of a boiler or gas water heater must be done by a Technical Safety BC licensed gas fitter. CANRO holds gas licence LGA0043870 and boiler licence LBP0046450. If you ever smell gas, hear hissing near a gas line, or suspect a carbon monoxide problem, leave the home immediately and call FortisBC at 1-800-663-9911 from outside before doing anything else.
Much of the region served by the reservoir system has relatively soft water, while some areas on well water, more common in parts of the Fraser Valley, have harder water. Your specific location affects how quickly scale accumulates.
Signs can include reduced hot water output, rumbling or popping sounds from a storage tank, or reduced flow and hot water temperature from a tankless unit. A technician can confirm scale is present during a service visit.
Left unaddressed for a long time, scale can reduce efficiency, damage heating elements or heat exchangers, and shorten equipment service life. Periodic flushing and maintenance help manage it before it becomes a bigger problem.
It depends on your specific local water hardness. In Metro Vancouver's generally soft-water areas, a softener may not be necessary, while homes on harder well water might benefit more. A technician can advise based on your actual water conditions.
Frequency depends on your local water hardness and usage. Manufacturers typically recommend periodic descaling, and a technician can suggest an interval appropriate for your specific water conditions and unit.
They're related but not identical. Scale is mineral deposits formed from dissolved minerals precipitating out during heating, while sediment can also include debris and particulates that settle in a tank. Both reduce performance over time.
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