Several persistent myths about tankless water heaters, from endless hot water to zero maintenance, don't hold up against how these units actually work.
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Common myths about gas tankless water heaters include the ideas that they provide truly unlimited simultaneous hot water regardless of demand, that they need no maintenance at all, that they always save dramatically on gas bills, and that they work during a power outage the same way an old standing-pilot tank did. Each of these has a kernel of truth but misses an important limitation: tankless units still have a maximum flow rate, still need periodic descaling and inspection, savings depend heavily on household usage patterns, and most models require electricity to ignite and run their controls.
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It's true that a correctly sized tankless unit won't run out of hot water the way a storage tank can during a long shower marathon, since it heats water continuously rather than drawing down a fixed reserve. But "unlimited" only applies within the unit's maximum flow rate at a given temperature rise. Ask three showers, a dishwasher, and a load of laundry to run hot water at the exact same moment, and an undersized unit will fall short just as clearly as an empty tank would, just for a different underlying reason.
Tankless units are often marketed around their compact size and on-demand convenience, which can leave the impression that they simply run forever without attention. In reality, mineral scale builds up inside the heat exchanger over time from normal water flow, and periodic descaling, along with inlet filter checks and combustion inspection, is part of keeping the unit performing the way it's designed to. Skipping this maintenance doesn't usually cause immediate failure, but it does lead to a gradual decline in efficiency and, over years, can shorten the unit's useful life.
| Household pattern | Realistic expectation |
|---|---|
| Low, spread-out hot water use | Efficiency gain from not maintaining a hot tank standby can be meaningful |
| Heavy, near-continuous hot water use | Smaller relative benefit, since a tank spends less time idling in standby anyway |
| Any household | No specific percentage of savings can be promised without knowing your actual usage and current equipment |
Tankless units avoid the standby heat loss that comes from keeping a full tank of water hot around the clock, which does offer an efficiency advantage in many households. But the actual dollar impact depends heavily on your specific usage pattern, your current equipment's condition, and gas rates, none of which support a specific savings percentage being stated with confidence for every household.
Many older storage tank water heaters with a standing pilot could continue producing hot water during a power outage, since they didn't rely on electricity to ignite. Most gas tankless units, by contrast, use electronic ignition, a control board, and often a combustion air fan, all of which need power to function. This means a power outage typically stops a tankless unit from producing hot water entirely, which is worth knowing if that continuity matters to your household, particularly given how often winter storms bring brief outages to parts of Metro Vancouver.
Because a tankless unit is compact, it's easy to assume it simply drops into place wherever the old tank was. In practice, gas line sizing, venting requirements, electrical needs, and condensate drainage are all specific to tankless units and often different from what an older storage tank needed, especially in an older home. A proper site assessment before installation catches these differences and avoids the surprise of discovering mid-installation that additional work is needed.
Safety note
Installation, venting, and gas connection for any gas tankless water heater must be performed by a Technical Safety BC licensed gas fitter. If you ever smell gas or suspect a carbon monoxide issue, leave the home immediately and call FortisBC at 1-800-663-9911.
Within their rated flow capacity, yes, they heat continuously rather than drawing from a fixed reserve, but demand beyond that capacity, such as too many fixtures running at once, will still exceed what the unit can supply.
No, periodic descaling, filter checks, and combustion inspection are part of keeping a tankless unit performing well over its life, similar in principle to any gas appliance needing periodic service.
It often improves efficiency by avoiding standby heat loss, but the actual savings depend on your household's usage pattern and current equipment, so no specific percentage can be promised.
Generally no, since most models rely on electricity for ignition and controls, so a power outage typically stops hot water production even though gas is still available.
Not always. Gas line sizing, venting, electrical, and condensate needs are often different for a tankless unit, so a proper site assessment is important before assuming a direct swap will work.
Many homes are good candidates, but sizing, venting options, and existing gas line capacity all affect whether a specific home's tankless installation will be straightforward or require additional work.
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