How each one works
A tank water heater keeps 40 to 50 gallons of water hot around the clock, ready when you need it. When the tank runs low, you wait for it to reheat.
A tankless water heater has no tank. When you open a hot faucet, it fires up and heats water as it flows through. It keeps going as long as you need hot water, but it can only heat so much at once.
Side by side
| Tank | Tankless | |
|---|---|---|
| Upfront cost | Lower | Higher, especially if the gas line needs upgrading |
| Hot water supply | Can run out | Doesn’t run out |
| Lifespan | About 8 to 12 years | 20 years or more with maintenance |
| Space | Large tank on the floor | Small unit on the wall |
| Standby energy | Keeps a tank hot all day | Only heats when you use it |
| Maintenance | Flush yearly | Descale yearly, especially with hard water |
When a tank makes sense
- Your budget is tight and the old tank simply needs replacing.
- You’re planning to sell in the next few years.
- Your household rarely runs out of hot water.
- Upgrading the gas line or venting would be expensive in your home.
When tankless makes sense
- You regularly run out of hot water.
- You want the floor space back in a garage or closet.
- You plan to stay in the home for many years.
- You’re remodeling, which makes gas and venting changes easier.
Installation costs people miss
Most surprise costs with tankless come from three things: gas, venting and water quality.
- Gas line size. Gas tankless units need much more gas while running than a tank, so many homes need a larger line, and sometimes a bigger gas meter.
- Venting. Tankless units need their own type of vent, which may mean a new route through a wall or the roof.
- Hard water. Scale builds up inside the heat exchanger, so plan for yearly descaling.
What about heat pump water heaters?
Heat pump water heaters are tanks that use electricity to move heat from the surrounding air into the water, instead of making heat directly. They’re very efficient but need space, airflow and an electrical circuit, and they work best in a garage or a large utility area.
Our take
For most households replacing an old tank on a budget, a new tank is the simple, reliable choice. If you run out of hot water, want the space back or plan to stay for years, tankless is worth a serious look. Either way, have the gas line, venting and permit handled properly. That’s where most problems start.