Hot Water Sized for a New Hampshire Winter

We install tankless water heaters for homes in Laconia and across the Lakes Region. Most of the questions we hear come down to one: will it keep up in January? Here is how to think about that before anyone quotes you a unit.

Will tankless keep up in winter?

A tankless water heater's output depends on two things:

1. How much hot water you use at the same time, measured in gallons per minute (GPM). A shower and a kitchen tap running together add up.
2. How many degrees the heater has to raise the water. This is the temperature rise: the temperature you want at the tap minus the temperature of the water coming into the house.

In winter the water coming into a New Hampshire home is colder than in summer, so the heater has to raise it by more degrees. The more it has to raise the water, the fewer gallons per minute a given unit can deliver. ^[1] A unit that easily ran two showers in August can struggle with the same two showers in February.

That is why a tankless heater is sized for your household's winter demand, using the manufacturer's published flow-versus-temperature-rise figures for that model, and not by the largest GPM number on the box. See how sizing works.

"Endless hot water" doesn't mean unlimited flow

A properly sized tankless heater heats water as it flows, so it does not run out the way a storage tank empties. ^[2] That is the real advantage.

But every unit has a maximum output at a given temperature rise. Open more hot taps than it can handle and the water gets cooler or the flow drops. The goal of sizing is to make that limit sit above the way your household actually uses water at its busiest time, on the coldest days.

What changes a tankless installation?

Two homes with the same heater can be very different jobs. Things that change the scope:

• Fuel. Natural gas, propane or electric, and whether the home already has the right fuel where the heater will go.
• Gas supply. A gas tankless heater can draw far more gas at full output than an old tank heater. The gas line, and sometimes the meter or propane regulator, has to be able to supply it. ^[2]
• Venting. Gas tankless heaters need their own vent system to the outdoors, installed to the manufacturer's instructions. Condensing models cannot vent through a chimney or share a vent with other appliances.
• Condensate. High-efficiency condensing models produce acidic condensate that has to be drained properly, and that drain must not freeze.
• Electrical. Gas tankless heaters still need electricity for their controls, fans and ignition.
• Location. Indoors or out, and how far it is from the fixtures that use the most hot water.
• Recirculation and piping. Whether you want faster hot water at distant taps, and what shape the existing piping is in.
• The old heater. Removal and disposal of the existing unit.
• Permits and inspection. Water heater and gas work is permitted and inspected work in New Hampshire.

This is why an honest estimate starts with seeing the existing setup. More on installation cost factors.

Tankless isn't always the only answer

A gas or propane tankless heater, a conventional storage tank, and a heat-pump water heater each suit different homes. The right choice depends on:

• the fuel your home already has
• how much hot water you use, and how much of it at once
• the space available and where the heater can go
• your electrical service
• how often you have long power outages
• your budget, and which incentives you qualify for

If a tank or a heat-pump water heater suits your home better, we will say so. Compare tankless, tank and heat-pump water heaters.

Freezing and power outages

Many tankless heaters protect themselves from freezing with built-in electric heaters, and that protection needs electricity. During a winter power outage a tankless heater cannot make hot water, and a unit in a cold space can be at risk of freezing unless it is protected as the manufacturer directs. ^[3] Outdoor and freeze-exposed installations need to be planned for this from the start. Read about maintenance and winter care.

Rebates and incentives

Some New Hampshire utility customers may be eligible for current incentives. Checked September 23, 2026:

• NHSaves natural gas water heating. Tankless heaters with a UEF of 0.87 or higher are listed at $500 on the 2026 rebate forms, for Liberty and Unitil natural gas customers only. Propane accounts do not qualify. ^[4]
• NHSaves heat-pump water heaters. $900 on qualifying ENERGY STAR models, for Eversource, Liberty, NHEC and Unitil electric customers. ^[5]
• Federal tax credit. The federal home-improvement credit for water heaters ended with equipment placed in service in 2025.

Eligibility depends on your utility and the model, programs change, and funds are limited. Confirm with NHSaves before you buy. More on rebates.

Permits and qualified installation

New Hampshire licenses gas fitters and plumbers, and state law treats installing a gas or propane water heater as gas-fitting work. Towns issue the permits. In Laconia, plumbing permits go only to licensed master plumbers, and gas permits come from the Fire Department before installation starts. Ask any installer who will pull the permits and who will be on site doing the gas and plumbing work. More about permits and choosing an installer.

Common questions

Will one tankless unit run two showers? Often, but it depends on your showerheads' flow, how cold your incoming water gets, and the model's output at that temperature rise. Some homes need a larger unit or two units.

Does tankless work in a New Hampshire winter? Yes, when it is sized for winter incoming-water temperatures and installed with freezing and power outages in mind.

Does a tankless heater need maintenance? Yes. Manufacturers call for periodic descaling and filter cleaning, and how often depends on your water.

See all questions

Areas we serve

We serve homes in Belknap, Carroll, Grafton and Merrimack counties, including Laconia, Gilford, Meredith, Belmont, Tilton, Franklin, Bristol, Plymouth, Wolfeboro and Alton. See the full service area.