Comparison
Tankless vs. tank water heaters
Updated · Editorial team; not yet technically reviewed
The verdict
A tank water heater is cheaper to buy and install and delivers a large burst of hot water, but it can run out. A tankless heater never runs out at its rated flow and uses less standby energy, but it costs more upfront, often needs gas line and venting upgrades, and needs regular descaling in hard water.
Side-by-side
| Tank | Tankless | |
|---|---|---|
| Hot water supply | Limited by tank size and recovery | Continuous, limited by flow rate |
| Upfront cost | Lower | Higher, more so if gas and venting must change |
| Standby heat loss | Yes, keeps a tank hot | None |
| Space | Floor space for the tank | Wall mounted, compact |
| Typical life | About 8–12 years | Often longer with maintenance |
| Maintenance | Periodic flushing, anode checks | Descaling (often yearly in hard water), inlet filter cleaning |
| Cold climates | Unaffected | Larger temperature rise lowers the flow rate it can deliver |
Which fits your home
- Tank tends to fit households that want the lowest installed cost, homes where the gas supply or venting would be expensive to upgrade, and homes with one big peak (several showers back-to-back).
- Tankless tends to fit households that run out of hot water with a tank, homes short on space, and owners planning to stay long enough for energy savings to count.
- Consider a heat pump water heater if you have electric service and space for it: it's often the most efficient choice for all-electric homes.
Sizing tankless correctly
Tankless heaters are sized by flow (gallons per minute) at a given temperature rise. Add the flow of fixtures you run at the same time, then find the rise from your incoming water temperature to about 120°F. Incoming water is much colder in northern winters, so the same unit delivers less flow there than in the South.
Common questions
Do tankless water heaters save money?
They reduce standby energy loss, so operating costs are usually lower. Whether that repays the higher installed cost depends on your usage, fuel prices and how much installation work is needed.
Why does my tankless water heater go cold in the middle of a shower?
Common reasons are demand above the unit's flow rate, scale buildup, a clogged inlet filter, or a flow rate too low to activate it. Descaling and cleaning the filter solve many cases.
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