Guides › Tankless

Tankless vs tank water heater: which is right for your home?

A tank water heater keeps a supply of water hot and ready. A tankless (on-demand) heater heats water only as it flows through. Neither is better for every home. The right choice depends on how your household uses hot water, what fuel and venting you already have, and how long you plan to stay.

How each one works

Tank (storage): a tank, commonly 30 to 80 gallons, keeps water at a set temperature using a gas burner or electric elements. When you use hot water, cold water refills the bottom and is reheated. Once the hot water in the tank is used up, you wait for it to recover.
Tankless (on-demand): when you open a hot tap, water flows through a heat exchanger and a powerful gas burner or electric elements heat it on the spot. There's no stored hot water, so it doesn't run out, but it can only heat so many gallons per minute at once.

Side-by-side comparison

	Tank	Tankless
Hot water supply	Limited to what's in the tank, then a recovery wait	Continuous, but limited by flow rate (gallons per minute)
Upfront cost	Lower for the unit and usually for installation	Higher; installation can cost more if gas line, venting or electrical upgrades are needed
Operating cost	Loses some heat from the stored water around the clock (standby loss)	No standby loss, so usually uses less energy for the same hot water
Space	Large footprint	Wall-mounted and compact
Expected lifespan	Commonly around 8 to 12 years	Often longer, commonly 20 years with maintenance
Maintenance	Flush sediment and check the anode rod periodically	Descale (flush) the heat exchanger periodically, especially with hard water; clean inlet filter
Power outage	Most gas tanks with a standing pilot still work	Needs electricity to run, even gas models

Lifespans vary a lot with water quality, installation and maintenance. Check the manufacturer's warranty for the specific model you're considering; it's a good clue to how long it's built to last.

Sizing matters more with tankless

A tank is sized by capacity and first-hour rating. A tankless unit is sized by how many gallons per minute it can heat at the temperature rise you need. The temperature rise is the difference between your incoming cold water and the hot water you want, and it's bigger in cold climates and in winter. A unit that easily runs two showers in a warm climate may only keep up with one in a cold one.

Add up the fixtures you realistically run at the same time (for example, a shower plus the dishwasher).
Check the flow rate on each (it's often stamped on showerheads and listed in appliance manuals).
Compare that total against the manufacturer's flow chart at your winter temperature rise, not the best-case number on the box.

Installation: the hidden part of the cost

Swapping a tank for a tank is usually straightforward. Switching from tank to tankless can involve more work:

Gas line: gas tankless units have much larger burners than tank heaters. The existing gas line and meter may need to be upsized.
Venting: gas tankless units need their own type of venting. An old metal flue from a tank often can't be reused.
Electrical: whole-house electric tankless heaters can draw a lot of current and may need multiple large circuits or even a service upgrade. Check your panel capacity before choosing electric tankless.
Condensate: high-efficiency condensing units produce acidic condensate that needs a drain, and often a neutralizer.
Permits: most areas require a permit for water heater replacement, especially when gas or venting changes.

Get a quote that spells out these items, not just the price of the unit.

Common tankless complaints (and what's behind them)

"Cold water sandwich": a short burst of cool water when you turn hot water off and back on quickly, while the unit re-fires.
Longer wait for hot water: the unit has to fire up and the water still has to travel through the pipes. A recirculation system can help.
Won't fire at low flow: each unit has a minimum flow rate to turn on. A barely-open hot tap may stay cold.
Scale buildup: hard water can coat the heat exchanger and cause error codes or reduced output. Regular descaling, and sometimes a water softener or scale filter, prevents it.

Which should you pick?

A tank often makes sense if:

Your current tank has kept up fine and you want the lowest upfront cost.
Your heater died and you need hot water back quickly with a simple like-for-like swap.
Upgrading the gas line, venting or electrical service would be expensive in your house.
You lose power often and have a gas tank with a standing pilot.

Tankless often makes sense if:

You run out of hot water regularly, for example with back-to-back showers or a large soaking tub.
You plan to stay in the home long enough for lower energy use and longer life to make up the higher upfront cost.
You need to free up floor space.
Your gas supply and venting can support it, or you're already doing work that makes the upgrade easier.

Tip: Don't decide during an emergency if you can avoid it. If your tank is getting old (see the signs in the guide below), get quotes for both options now so you can choose calmly instead of taking whatever is on the truck the day it fails.

When to call a plumber

You want a proper sizing calculation for a tankless unit based on your fixtures and climate.
Switching would involve changes to gas piping, venting or electrical service; these should be done by licensed professionals with a permit.
You smell gas or your CO alarm goes off at any point. Leave the house and call your gas utility or 911 from outside.