Natural Gas Tankless Water Heaters: Models to Compare Before You Replace Your Tank

Your old tank leaks a little at the base, the shower runs cold when the dishwasher starts, and the utility closet is crowded with a cylinder you would love to reclaim. Those are the usual triggers for a switch to a tankless heater, which warms water only when a tap opens. The best natural gas tankless hot water heaters pair enough heating capacity for your household with a venting layout your home can accommodate, since gas models need a proper exhaust path and gas line.

Because installation is part of the purchase, this guide covers sizing and venting rules before reviewing five models by manufacturer and model code. Model numbers ending in N typically indicate natural gas, but always confirm fuel type on the nameplate. As of 2026, condensing designs are common in new installations, and local code, permits and a licensed installer are part of nearly every project.

Quick Picks

The five models below are listed by manufacturer and model code. Flow rate and capacity are not in the codes, so confirm them in the manufacturer’s specification sheet and match them to your fixtures before choosing.

How to Choose

A tankless heater is as much an installation project as an appliance purchase. The four rules below cover sizing, gas supply, efficiency and upkeep, and a licensed installer should confirm each one against your home before any equipment is ordered.

Size by flow rate and temperature rise

Add up the gallons per minute of fixtures you may run at the same time: a shower is often about 2 gallons per minute, a dishwasher about 1.5 and a bathroom faucet about 1. Then calculate temperature rise by subtracting your incoming water temperature from the 120 degree setting. A heater must deliver your total flow at that rise. In cold climates where incoming water is near 40 degrees, a bigger unit is necessary.

Confirm gas line and venting needs

Tankless gas heaters draw large amounts of gas in short bursts, so the existing half-inch line often needs upgrading to three-quarter inch. Venting can be direct vent, which draws air from outside, or power vent, which uses indoor air. Condensing units can use PVC pipe, while non-condensing units require stainless steel. Ask for a quote that includes gas piping, venting and any permits.

Look at efficiency type

Condensing models achieve a uniform energy factor of about 0.90 or higher, while non-condensing models are typically around 0.80 to 0.82. Condensing units cost more up front but can use less gas over their lifetime. They also produce acidic condensate that needs a drain and, in some places, a neutralizer. Check whether your area offers rebates for high-efficiency equipment.

Plan for water quality and maintenance

Hard water can create scale inside the heat exchanger, so plan to flush with vinegar or a descaling solution about once a year. A water softener helps if your supply is above roughly seven grains per gallon. Look at warranty terms: heat exchangers commonly carry 10 to 15 year coverage, but parts and labor are often shorter. Ensure the unit has an accessible filter and drain valves.

Our Picks Reviewed

These five models come from established tankless and water heater makers. Model codes reveal little about flow rate, so the reviews concentrate on what the brand and code suggest, such as direct venting or natural gas fuel. Verify capacity, venting and clearance requirements in the installation manual, and compare quotes from more than one installer.

Rinnai RU199iN

Rinnai is among the best-known tankless brands, and the RU199iN code includes an N for natural gas and an i for indoor.

• Pro: a leading tankless brand generally has a broad installer network, which eases service.
• Pro: the larger model number family typically targets bigger households with multiple bathrooms.
• Con: indoor units need venting through a wall or roof, which raises installation complexity.
• Skip it if you have a small household with one bathroom, where a smaller unit may be enough.

It suits families who want serious capacity from an established name. Ask the installer to size it to your fixtures, confirm the gas line, and discuss maintenance. Registering the product soon after installation helps preserve warranty coverage.

Navien NPE-240A2

Navien specializes in tankless and condensing technology, and the NPE-240A2 is a model in its NPE series.

• Pro: a specialist brand tends to design around efficiency and continuous hot water supply.
• Pro: model families from tankless makers often offer built-in recirculation options, though you should confirm this for the specific model.
• Con: high-efficiency designs require condensate drainage and compatible venting.
• Skip it if your home cannot handle the venting and drain needs without a major remodel.

It is a fit for homes with larger demand, such as multiple showers or a big soaking tub. Verify that the model is the natural gas version before ordering, because some Navien models ship for either fuel. A licensed installer should review your flue, gas line and electrical outlet.

Noritz NRC981-DV-NG

Noritz is another established tankless maker, and the model code includes DV for direct vent and NG for natural gas.

• Pro: direct vent design draws combustion air from outside, which protects indoor air quality.
• Pro: the code states fuel type clearly, reducing ordering mistakes.
• Con: direct vent requires two pipes through the wall or roof, which adds planning.
• Skip it if your home lacks a practical route for exhaust and intake piping.

It suits tight, well-sealed homes where indoor combustion air is a concern. Confirm the clearance requirements near windows and doors, and ask whether your climate requires freeze protection. A well-planned vent run keeps noise low and installation cleaner.

Rheem RTGH-95DVLN

Rheem is a major water heater manufacturer, and DV in the code points to direct venting.

• Pro: a large manufacturer provides an extensive parts and service network.
• Pro: direct venting suits homes where indoor air should be preserved.
• Con: the code does not tell you flow rate, so confirm capacity against your needs.
• Skip it if you cannot arrange for a gas line upgrade or exterior vent route.

It fits homeowners who value brand familiarity and widely available service. Ask your installer whether the unit’s venting works with existing penetrations, and review the warranty terms for the heat exchanger and parts. Many homeowners also add isolation valves for easier yearly flushing.

Takagi T-H3-DV-N

Takagi has a long record in tankless heaters, and the T-H3-DV-N code signals a direct vent natural gas model.

• Pro: tankless specialists often focus on reliability and straightforward controls.
• Pro: direct vent and natural gas are both clearly stated in the code.
• Con: smaller brand recognition may mean fewer local installers familiar with it.
• Skip it if your plumber prefers other brands and will not service this one.

It suits buyers who research installers first and choose equipment they can service. Ask for a written scope of work, including gas line sizing, venting materials and condensate handling. A thorough quote avoids surprises, and annual maintenance keeps performance steady.

Which One Fits

Household size and layout matter most. A large family with several bathrooms needs the biggest capacity, while a couple in a small home may be well served by a smaller unit. Homes with tight utility closets benefit from direct vent models, and buyers in cold regions should prioritize capacity at low incoming water temperature. Local installer familiarity is a strong tiebreaker.

• Large families wanting a recognized brand: Rinnai RU199iN.
• High-demand households: Navien NPE-240A2.
• Sealed homes needing direct vent: Noritz NRC981-DV-NG.
• Buyers who value large-brand service: Rheem RTGH-95DVLN.
• Researchers who select by installer: Takagi T-H3-DV-N.

Hot water also pairs with cleaning routines; read about the best multi purpose steam cleaners for chemical-light cleaning, and see the best mop for hard floors for the rest of the house.

Common Mistakes

Keep the installation manual, the model label photo and the installer’s invoice together in one folder, because warranty claims and future service visits go much faster when those documents are easy to find.

Most tankless problems stem from planning gaps rather than faulty equipment. Reviewing the following points before the installer arrives can prevent cold-water complaints, failed inspections and avoidable repair calls.

• Undersizing the unit. Add all simultaneous fixtures and cold-season water temperature.
• Ignoring gas line capacity. A small line starves the burner.
• Choosing the wrong fuel version. Confirm natural gas on the model label.
• Skipping maintenance. Annual flushing prevents scale.
• Forgetting permits. Gas work usually requires a licensed professional and inspection.

FAQ

Switching to tankless brings questions about energy use, lifespan and installation. The short answers below are general, and local code and your installer’s advice always take priority. Before signing a contract, ask each installer for a written quote that lists gas line work, venting materials, permits, condensate handling and the warranty terms for both equipment and labor. Comparing at least two quotes line by line reveals scope differences that can matter more than the price gap between models, and it helps you avoid surprise add-ons after the old tank has been removed.

Do tankless heaters save energy?

They avoid standby heat loss, which often lowers gas use, particularly in smaller households.

How long do they last?

With maintenance, many run 15 to 20 years, longer than most tank models.

Can I install one myself?

Gas and venting work should be done by a licensed professional to meet code.

Why does the water turn cold briefly?

Short cold bursts can occur when you stop and restart flow quickly. A recirculation setup reduces it.

Will it work during a power outage?

Most need electricity for controls and fans, so plan a backup if outages are frequent.