Tank vs tankless water heater: the honest pros and cons

How they differ

A tank heater keeps a full tank of water hot around the clock. A tankless heater heats water only as it flows through. That's where the savings come from: no tank losing heat while nobody's using water.

Energy savings: real but variable

The DOE's Energy Saver Guide says on-demand heaters can be 24% to 34% more efficient for homes using 41 gallons or less a day, and 8% to 14% more efficient for homes using a lot, around 86 gallons a day. A DOE Building America field study adds a caution: savings vary a lot with how much water each use draws. Tiny draws are less efficient, and the greatest savings came at about 50 gallons a day.

Lifespan

A DOE Building America study used an expected life of 20 years for tankless units and 13 years for tanks. InterNACHI's chart is more conservative for on-demand heaters at about 10 years. Regular descaling is what pushes a tankless toward the long end.

Upfront cost

Angi's 2026 data puts tank replacement at $882 to $1,826 and tankless at $1,400 to $3,900 installed. HomeGuide gives $600 to $3,100 for tanks and $1,400 to $5,600 for tankless. Switching from a tank to tankless can cost more than a like-for-like swap if gas lines, venting or electrical service need upgrading.

The downsides of tankless

• Simultaneous use. The DOE notes that if you use hot water in several places at once, you may need two or more tankless units to keep up.
• Power outages. Bradford White says any water heater that needs external power won't make hot water while the power's out. Many tankless units, gas ones included, need electricity for their controls, so check before you buy.
• Descaling. A. O. Smith says many tankless heaters need descaling with a cleaning solution and kit. In hard water that's a regular job.
• Repair costs. HomeGuide puts tankless repairs at $300 to $1,300.

The downsides of a tank

• Standby heat loss, so higher running costs for most homes
• A shorter life and the risk of a tank leak at the end of it
• Hot water that runs out after a long run of showers
• Yearly flushing to manage sediment

Which is right for you?

Tankless tends to make sense if you plan to stay in the home for years, your daily use is moderate, and you're willing to descale. A tank is often the better value if your budget is tight, your existing tank is being replaced like for like, or your household runs several showers at once. When the tank fails, you don't have to decide in a rush: a plumber can quote both.