Q: I'm considering installing two tankless water heaters, one set to a high temperature for the washing machine and dishwasher, the other at a lower temperature for the bathroom to avoid being scalded. Does this make sense?

—Robert Norko, North Haverhill, N.H.

A: Richard Trethewey replies: Not really. Tankless water heaters are expensive, and a single unit, if properly sized, will easily handle the needs of most houses. Just set the unit's water temperature to a nonscalding 120 degrees or so and you'll meet most of your cleaning needs, including clothes washing. Dishwashers do need hotter water than that, so many machines have an internal heater to boost the water to 130 or140 degrees. If yours doesn't already hahave such a heater, it's less expensive to buy a new dishwasher than another tankless unit.

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