What a tankless unit changes

A storage heater keeps a tank hot and waits. A tankless unit fires when you open a hot tap and heats the water on the way past. Nothing stands by losing heat, and the hot water does not run out at the end of a tank.

Flow rate is the ceiling, not volume. A unit sized around one shower can fall behind when a dishwasher and a second shower join in, so that conversation belongs before the purchase rather than after. Federal figures put these units past 20 years of service.

What a conversion involves

Swapping a tank for a tankless unit is more than a like for like change.

  • Sizing the unit to the fixtures you run at once, not to the old tank
  • Gas line sizing, since a gas tankless unit draws far more than a tank burner
  • A dedicated vent, because most units cannot use the old flue
  • Electrical supply for an electric unit, which can mean panel work
  • Isolation valves at the unit so it can be descaled without draining the house
  • Somewhere to mount it, indoors or on a protected outside wall

The plumber prices all of that in the estimate, so the number you compare covers the work and not the price of the box.

Keeping one working

Tankless units need descaling on a schedule. Minerals build up on the heat exchanger, output drops and the unit starts throwing error codes. With isolation valves fitted, a descale is a short visit with a pump and a bucket.

If a unit is already fitted and the hot water has gone weak or the burner cuts out under load, book a service call. Descaling, a cleaned inlet filter or a vent check fixes a good share of those.

Common questions

How long do tankless water heaters last?

Past 20 years on most models by federal estimates, against 10 to 15 on a storage tank. Components are replaceable too, which a rusted tank cannot claim.

Will one unit run two showers?

That comes down to flow rate and how cold the incoming water runs. Sizing follows the fixtures you expect to run at once, so say up front if two showers and a washer overlap on a school morning.

Do I have to descale it?

Yes, on a schedule set by the manufacturer and by how hard your water is. Fitting isolation valves at install time makes that a short job later.

Can it go on an outside wall?

Some units are rated for outdoor mounting, which suits a house with no good indoor spot. On the coast, ask about the location, the housing and salt air before you settle on it.