Water Heaters & Boilers

Tankless water heaters and condensing combi-boilers from Navien, Rinnai and A. O. Smith.

How to choose a tankless water heater or boiler

A tankless water heater heats water only when you open a tap, so it never runs out and does not waste energy keeping a tank hot. Sizing is about flow and temperature rise, not tank gallons.

1

Flow rate (GPM)

Add up the fixtures that run at the same time: a shower uses about 2 GPM, a kitchen faucet about 1.5 GPM and a dishwasher around 1–1.5 GPM. Two showers and a sink need about 5–6 GPM.

2

Temperature rise

Subtract your incoming groundwater temperature from the hot water you want (usually 120 °F). Northern homes need a bigger rise, so they need a more powerful unit for the same flow.

3

Condensing

Condensing units recover heat from the exhaust and reach efficiency above 90%, which lowers gas bills and allows PVC venting.

4

Combi-boiler

A combi-boiler heats your home and your domestic hot water from one wall-hung appliance, freeing floor space.

Read the full buying guide

Questions & answers

Can I replace a tank heater with a tankless unit?

Usually yes, but gas tankless units often need a larger gas line and new venting. Have a licensed plumber confirm gas supply and venting before you order.

Indoor or outdoor model?

In warm climates an outdoor model saves venting costs. In cold climates, indoor units are the norm.

Do tankless heaters need maintenance?

Yes: flush the heat exchanger about once a year, more often with hard water, to prevent scale.

Not sure which model fits? Ask our team and a real person will answer within one business day.