Tankless versus tank
A tankless heater is not a better water heater. It is a different set of trade-offs, and which one wins depends on things that have nothing to do with the unit.
What tankless genuinely gives you
- Unlimited duration. Not unlimited flow, unlimited duration. It cannot run out, though it can fail to keep up.
- No standby loss. A tank reheats water nobody is using. Tankless does not.
- Space, and long life. No cylinder, and a longer service life than a tank if it is descaled.
What it costs you
- Flow limits in winter. The whole subject of this site.
- Installation. A larger gas line, new venting, and for electric a service that can cost more than the heater.
- Descaling. In hard water a tankless unit needs flushing periodically, and neglecting it is the main cause of premature failure.
- The cold water sandwich. Short draws in quick succession can deliver a slug of cold water between them.
When a tank is the better answer
- Cold climate, high simultaneous demand. If the honest calculation says two units, a single tank may serve better for less money.
- Electric with a modest service. A heat pump water heater is usually the stronger electric option, and draws a fraction of the current.
- Short, infrequent draws. Standby loss is small in a modern insulated tank, and the cold water sandwich is most annoying in exactly this pattern of use.
When tankless clearly wins
Warm climate, gas already sized, long showers, limited space, or a household whose complaint about the current heater is that it runs out rather than that it is slow. Those are the cases where the trade is straightforwardly good.
Run your own numbers first, because the answer turns on the temperature rise more than on anything a brochure will tell you.
Frequently asked questions
Is a tankless water heater worth it?
In a warm climate with gas already in place, usually yes. In a cold climate with high simultaneous demand, often not: the honest sizing calculation frequently calls for two units, and a tank does the job for less. The deciding factor is temperature rise, not the unit.
Do tankless water heaters really save money?
They remove standby loss, which is real but modest in a modern insulated tank. Against that, installation costs more and descaling is an ongoing job. Payback is usually measured in many years and depends heavily on how much hot water the household uses.
What is the cold water sandwich?
A slug of cold water between two short hot draws. The first draw leaves hot water in the pipe, the heater shuts off, and the next draw pulls that hot water through followed by the cold that was behind it before the burner catches up. Some units mitigate it with a small buffer tank.
How long do tankless water heaters last?
Commonly 15 to 20 years, longer than a typical tank, provided the heat exchanger is descaled on the schedule the manufacturer sets. In hard water, skipping that is the usual cause of early failure.