How each one works
A tank heater keeps a fixed volume of water hot and ready, reheating it as you use it. When the stored hot water runs out, you wait for the tank to recover.
A tankless heater stores nothing. When a hot tap opens, it senses flow and fires a burner or elements to heat water as it passes through a heat exchanger. It does not run out the way a tank does, but it can only heat so many gallons per minute at once.
Side by side
Tank
- Simple, familiar installation in a garage or closet
- Usually fits the existing vent and gas connection on a like-for-like swap
- Hot water limited by stored volume and recovery
- Sediment settles in the tank and benefits from flushing
- Must be seismically strapped in California
Tankless
- Compact, often wall-mounted outside
- Gas units often need different venting and more gas supply than a tank
- Continuous hot water up to its flow limit
- Scale builds in the heat exchanger and needs periodic descaling
- Needs electrical power even on gas models
Questions that decide it
| Question | Points toward tank | Points toward tankless |
|---|---|---|
| How much space do you have? | An existing tank spot you are happy with | You want the garage or closet space back |
| How many showers run at once? | Large simultaneous use and a big tank | Use spread through the day, or a unit sized for peak flow |
| Can the gas line supply more? | Existing line is modest | A plumber confirms the line and meter can carry it |
| Will you keep up maintenance? | Prefer occasional flushing | Willing to descale on the manufacturer's schedule |
| Budget for the change itself | Lowest disruption | Accepting venting, gas or electrical work |
If you are considering a switch to tankless
- Have the gas supply checked.A plumber should confirm whether the existing gas line can carry the larger load, or whether it needs upsizing.
- Plan the venting.Many gas tankless units use dedicated venting different from a tank's vent pipe. The location affects how simple that is.
- Confirm power.Tankless units need an electrical outlet or circuit for controls, even when they burn gas.
- Size for your peak.Count the fixtures you run together and the temperature rise needed. Undersizing means lukewarm water at busy times.
- Ask about permits.Changing heater type is more than a swap. Check with the city about permit and inspection requirements.
Terms you will hear
- First-hour rating
- How much hot water a tank can deliver in an hour starting full. Printed on the label.
- Flow rate (GPM)
- Gallons per minute a tankless unit can heat at a given temperature rise.
- Temperature rise
- The difference between incoming water temperature and the temperature you want at the tap.
- Recovery
- How quickly a tank reheats after hot water has been used.
Common questions
- Will a tankless heater fit where my tank was?
- Sometimes, but many are mounted on an exterior wall instead. Location depends on venting, gas supply and where the water lines run.
- Do tankless heaters really never run out?
- They do not run out the way a tank does, but they have a flow limit. Ask too much at once and the water gets cooler.
- Is switching to tankless a simple swap?
- Usually not. Expect possible gas line, venting and electrical work, and check with the city about permits.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.