How they differ
A tank keeps a set volume of water hot all the time. A tankless unit heats water only when a tap opens. That's the source of every trade-off below.
Choose a tank if…
- Your budget is focused on upfront cost
- Your gas line is small or you're on electric with limited panel capacity
- You'd rather not schedule yearly maintenance
Choose tankless if…
- You run out of hot water with a tank
- You want to free up floor space
- You plan to stay in the home long enough for energy savings to add up
The installation questions that decide it
Gas tankless units often need a larger gas line than a tank, plus new venting. Electric tankless units can need a large electrical service. Those costs vary more than the unit price does, so get them assessed before you choose.
What changes during a tankless conversion
Switching from a tank to a gas tankless unit usually means a larger gas line, new stainless or PVC venting, and a dedicated electrical outlet. Electric tankless units often need a large electrical service upgrade. Those extras, not the heater itself, drive most of the difference in installed cost.
Tankless heaters also need periodic descaling, especially where water is hard, to keep the heat exchanger working efficiently.
Tank vs. Tankless Water Heaters: when to call a pro
- Error codes on the unit display
- Water fluctuates between hot and cold
- Unit shuts off during use
- Hasn't been descaled in over a year
Tank vs. Tankless Water Heaters: common questions
Will a tankless water heater run out of hot water?
No, but it has a flow limit. If several showers and appliances run at once, a unit that's too small will deliver cooler water. Correct sizing by gallons per minute avoids that.
How long do tankless water heaters last?
Well-maintained tankless units commonly last around 20 years, compared with about 8 to 12 years for a typical tank heater.
Is a tankless water heater worth it?
It can be if you need endless hot water, want to save space, and have a gas line and venting route available. Installation costs more than a tank swap, so savings depend on usage and fuel prices.
Do tankless water heaters need maintenance?
Yes. Most manufacturers call for periodic descaling and cleaning of the inlet filter.
Every home differs; editorial standards.