A homeowner in Dunkirk called us after their 12-year-old 40-gallon electric water heater finally failed — the bottom element had burned out and the tank had developed a slow leak at the drain valve. They had been researching tankless water heaters and wanted to upgrade rather than replace with another tank unit. They had a family of four and frequently ran out of hot water during morning showers. They had also heard that tankless water heaters could be problematic with well water and wanted honest advice before committing to the upgrade.

We tested the water before sizing the unit. Iron was 3.8 ppm, hardness was 17 GPG, and pH was 6.7. The hardness level was the primary concern for a tankless water heater — hard water deposits scale on the heat exchanger, which reduces efficiency and can cause premature failure. At 17 GPG, scale buildup would be significant without treatment. We recommended a whole-home scale inhibitor (template-assisted crystallization, or TAC) upstream of the water heater to prevent scale without adding salt. We also recommended a water softener for the full home, but the homeowner wanted to address the water heater first. We sized the tankless unit for the home's peak demand: a family of four with two simultaneous showers requires approximately 5–6 GPM at a 70°F temperature rise.

1. 1Tested water: iron 3.8 ppm, hardness 17 GPG, pH 6.7 — identified scale risk for heat exchanger
2. 2Calculated peak demand: 2 simultaneous showers + 1 fixture = 5.5 GPM at 70°F rise
3. 3Selected Rinnai RU199iN (199,000 BTU) — sized for peak demand with capacity margin
4. 4Installed TAC scale inhibitor on cold water supply to water heater — prevents scale without salt
5. 5Ran new 3/4" gas line from meter to water heater location — existing 1/2" line undersized for unit
6. 6Installed concentric PVC vent through exterior wall — sealed and weatherproofed
7. 7Installed isolation valves and flush ports for annual descaling maintenance
8. 8Registered unit with Rinnai for 12-year heat exchanger warranty
9. 9Tested unit at full flow: 5.5 GPM at 120°F output — consistent temperature throughout test

The homeowner now has unlimited hot water — no more running out during morning showers. The Rinnai RU199iN delivers consistent 120°F water at the full 5.5 GPM peak demand. The TAC scale inhibitor protects the heat exchanger from the hard water that would otherwise cause premature failure. The unit is registered for the 12-year heat exchanger warranty. The homeowner's electric bill dropped significantly — a tankless unit only heats water on demand, eliminating the standby heat loss of a tank unit.

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