Not a swap. A conversion.Replacing a storage tank with a tankless water heater in Cleveland.

What actually changes

The wall box is the easy part.

A conversion replaces a storage water heater with an on-demand unit. The new heater is usually smaller and wall-mounted, which frees basement floor space. Almost everything around it may change.

DOE Building America guidance on transitioning to tankless is blunt about infrastructure: gas supply, venting, and water piping often have to be reworked, and electric tankless can demand a large electrical service.^[1]

1. Gas supply

A typical gas storage tank sips fuel compared with a whole-home tankless burner at full fire. The existing half-inch run that was fine for the tank may be too small once the furnace, stove, and tankless unit can all call for gas at once. Sometimes the meter needs attention from the utility. That discovery should happen at the quote visit, not at mid-install.

2. Venting

The old draft-hood vent — the metal pipe into a chimney — is rarely the right vent for a tankless unit.^[1] Condensing models often use plastic pipe out a sidewall, with clearances to windows, doors, and grade. In a Cleveland winter, a sidewall termination needs to stay clear of snow drifts. Non-condensing models use different materials. If the old tank was the last appliance on a masonry chimney, converting it can leave a chimney that now needs a cap or liner for whatever remains.

3. Water lines and isolation valves

The tankless unit will not sit on the same footprint. Hot and cold lines get rerouted. Isolation (service) valves let someone descale the heat exchanger later without cutting pipe. Given Cleveland Water's reported hardness range of 105–130 mg/L as CaCO3, those valves are not a nicety.^[2]

4. Condensate

Condensing tankless units make acidic condensate that needs a drain, often with a neutralizer. A dry basement corner with no drain nearby complicates the job.

5. Power

Gas tankless units still need electricity for ignition, fans, and controls — usually a nearby outlet. Whole-home electric tankless is a different scale of electrical work.^[1]

When conversion is a good conversation

• The household regularly runs out of hot water and a larger tank would not fix simultaneous use
• Natural gas is already in the house (about 77.9% of occupied Cleveland homes use utility gas for space heat)^[3]
• There is a clean sidewall path for a new vent
• Someone will keep up with descaling

When a new tank is the wiser quote

• The current tank simply reached the end of a normal 10–15 year life^[4] and the vent and gas line are sound
• The gas service cannot support the extra input without major work
• There is no good vent path
• The house is all-electric and a heat pump water heater fits the basement better^[4][5]

Use the sizing calculator to sketch flow and temperature rise, then send the form. Mention that you are asking about a conversion so the installer looks at gas and venting, not just the old tank.

FAQ

Conversion questions.