Tankless Water Heater Questions From Lakes Region Homeowners

Will one tankless unit run two showers?

Often, yes, but it depends on three things: your showerheads' actual flow, how cold your incoming water gets in winter, and what the specific model delivers at that temperature rise. The Department of Energy notes that even a large gas unit can be stretched by simultaneous uses such as a shower and a dishwasher, and that some homes use two units. ^[1] See sizing.

Does tankless work in a New Hampshire winter?

Yes, when it is sized for winter conditions and installed with freezing and power outages in mind. Colder incoming water means the heater has to raise it by more degrees, which lowers the flow a given unit can deliver.

What does GPM mean?

Gallons per minute: how much water flows. For sizing, it is the total hot water flowing from everything that runs at the same time.

What is temperature rise?

The number of degrees the heater has to warm the water: the temperature you want at the tap minus the temperature coming in. The Department of Energy suggests assuming 50°F incoming water unless you know otherwise; your actual winter water may differ. ^[2]

Why can't I size it by the number of bathrooms?

Because the heater doesn't care how many bathrooms you have. It cares how much hot water flows at the same moment, and how cold that water starts. Two households with the same number of bathrooms can have very different peak demand.

Can I reuse my current gas line?

Sometimes. A gas tankless heater can draw far more gas at full output than the tank it replaces, so the line has to be checked against the heater's full input, and sometimes the meter or a propane regulator as well. ENERGY STAR lists this as one of the first things an installer should confirm. ^[3]

Can I reuse my existing vent?

Usually not. Condensing tankless heaters need their own venting to the manufacturer's specifications and cannot vent through a chimney or share venting with other appliances. ^[4]

What happens if the power goes out?

A tankless heater needs electricity to make hot water, so it won't work during an outage. Its freeze protection also needs power, so in freezing weather a long outage calls for the manufacturer's freeze precautions, such as draining the unit or a backup power source. ^[5]

Does a tankless heater need maintenance?

Yes. Manufacturers call for periodic descaling to remove mineral buildup and cleaning the inlet filter. How often depends on your water and your model. See maintenance and winter care.

Tankless or a conventional tank?

Tankless doesn't run out the way a tank does, avoids standby heat loss and saves space, but it has an output limit at any moment and usually needs more gas and venting work. A tank is usually the simpler replacement. Compare them.

What about a heat-pump water heater?

It is an efficient electric storage heater, and often the best fit for homes without gas or propane. It needs space and air around it, and it cools the room it sits in. NHSaves currently offers a rebate on qualifying models. Compare the options.

Are rebates available?

For some homes. As of September 23, 2026, NHSaves lists a $500 rebate for a qualifying natural gas tankless heater (0.87 UEF or higher) on both the Liberty and Unitil 2026 forms; it is for those utilities' natural gas customers only, not propane accounts. ^[6] NHSaves also offers $900 on qualifying ENERGY STAR heat-pump water heaters for Eversource, Liberty, NHEC and Unitil electric customers. ^[7] The federal Energy Efficient Home Improvement Credit does not apply to equipment installed in 2026. ^[8] Programs change and funds are limited, so confirm before you buy.

Why does installation price vary so much?

Because most of the work is around the heater: gas supply, venting, condensate drainage, electrical, location, piping, removing the old heater, and permits. See what changes the cost.

Do permits apply?

Yes. In Laconia, plumbing permits are issued only to New Hampshire licensed master plumbers, and gas permits are issued by the Fire Department before installation begins. ^{[9] [10]} Other towns run their own permit processes. More on permits and licensing.