How to Pick a Tankless Water Heater

Sizing is the decision that matters

Tankless units are rated by how much temperature rise they can deliver at a given flow rate. Both halves matter. A unit that comfortably runs one shower may not run a shower and a dishwasher at once, and incoming water temperature changes the answer with the season.

Groundwater here arrives cold in winter, which means the unit has to lift it further to reach a usable temperature, which reduces the flow it can deliver. A unit sized on summer performance will disappoint in January. Sizing is done against the coldest case, not the average.

Gas or electric

Gas units generally deliver higher flow and suit whole-house duty. They need a gas line capable of their full rated demand, and on a retrofit the existing line is frequently too small. That upgrade is part of the real cost and is often left out of a quote that looks cheap.

Electric units avoid venting and gas work entirely but draw heavily, and whole-house electric tankless often means a service panel upgrade. They suit point-of-use duty well.

Venting

Gas tankless units need their own vent, and they cannot generally share the flue of the appliance they replaced. Where the unit can go is usually decided by where a vent can reasonably run, not by where the old tank stood.

Installation details that decide the next ten years

Isolation valves, so descaling is a routine job rather than a cutting job. A sediment filter where the supply warrants it. Softening ahead of the unit on hard water. None of these are exciting and all of them are cheaper to do at installation than later.

What we would ask about your house

Fixture count and likely simultaneous demand, the size of the existing gas line, where a vent can run, and how hard the incoming water is. Those four answers narrow the choice quickly, and they matter far more than the brand on the front.