Best Condensing Tankless Hot Water Heaters: Featuring Units With High Efficiency Ratings

Our Verdict and How We Chose

The Rinnai RU180iP Condensing Tankless Hot Water Heater is the best Condensing Tankless Hot Water Heater because it delivers a high 10 GPM flow rate for large households.

Upgrading to a condensing unit often feels overwhelming because the technical differences between high-flow and high-efficiency models can be difficult to decipher. Choosing the wrong configuration can lead to a system that fails to keep up with multiple simultaneous fixtures, leaving you with a lukewarm shower during peak usage.

The Rinnai RU180iP solves this by providing a consistent 10 GPM flow, making it the primary choice for high-demand homes. You should consider the Rinnai RU160eN if you require a specialized outdoor installation, or the Noritz NRC66DVNG if you need a budget-friendly entry point with a 6.6 GPM capacity.

We evaluated the tankless water heater installation options we track against this topic’s criteria at Green Writer. The selected models cover a price range from $489.99 to $1703.1, with a median price of $1336.

If your home runs on liquid fuel, see our guide to the best propane tankless hot water heater options.

Full Comparison Table

Prices are approximate and move frequently – check the current price before deciding. “Not stated” means the manufacturer listing does not give that figure – we do not estimate it.

The Rinnai RU180iP offers the strongest price-to-spec ratio because it provides the highest 10 GPM flow rate for $1336.

The Picks Reviewed in Detail

The 3 picks below run from $489.99 to $1703.10, reviewed in rank order.

Rinnai RU180iP Condensing Tankless Hot Water Heater

The Rinnai RU180iP is our top-performing indoor selection for those upgrading to a high-capacity condensing system. It balances a high flow rate with advanced recirculation features to ensure consistent temperature across a large home.

What we like: The RU180iP provides a flow rate of up to 10 GPM, which exceeds the 3.5 GPM threshold required for a standard shower. It includes Circ-Logic for pairing with an external pump to provide scheduled or on-demand recirculation. The unit also carries a 15-year residential warranty on the heat exchanger.

Keep in mind: This model is designed for high-demand indoor use and may be over-specified for small apartments or single-bathroom households.

Rinnai RU160eN Condensing Tankless Hot Water Heater

The Rinnai RU160eN serves as the premium outdoor option for homeowners who require a condensing unit but lack indoor mounting space. It provides the same core technology as the indoor models but in a weather-ready configuration.

What we like: This unit delivers a 9 GPM flow rate and features a Uniform Energy Factor of 0.95. It supports up to 6 appliances simultaneously and includes a 5-year residential warranty on labor.

Keep in mind: Because this is an outdoor unit, you must confirm your mounting location meets local clearance requirements and is accessible for a qualified installer.

Noritz NRC66DVNG Indoor Condensing Tankless Hot Water Heater

The Noritz NRC66DVNG is the most budget-friendly entry point for a condensing tankless hot water heater. It offers a high-efficiency, low-NOx solution for those looking to upgrade without a high price tag.

What we like: Priced around $489.99, this model includes a remote thermostat and a 6′ power cord. It is designed for high efficiency and low NOx emissions while providing endless hot water.

Keep in mind: With a 6.6 GPM flow rate, this unit may experience a flow rate shortfall if you attempt to run multiple high-demand fixtures like two showers and a sink at once.

Household Flow Rate and Space Requirements

To determine how many gallons per minute (GPM) you need, calculate your peak usage; a 10 GPM flow rate like the Rinnai RU180iP allows for multiple simultaneous fixtures without temperature drops. If you plan to run multiple showers and a sink at once, you should aim for a unit that can sustain at least 10 GPM. Many buyers mistakenly choose a low-flow unit that fails to keep up with concurrent demands, resulting in cold water mid-shower. Regarding space, you must measure your available wall or floor area and confirm the required service zone for the specific model’s clearance. Because these units require specific clearances for maintenance and venting, check the manufacturer’s dimensions against your utility closet or outdoor mounting site before ordering. A qualified installer must perform the final mounting to ensure compliance with local building codes.

The Specs That Decide This Purchase

Condensing Efficiency Rating

Condensing efficiency rating determines how much fuel is converted into heat versus lost through the exhaust. You should prioritize units with a high Uniform Energy Factor (UEF) to maximize long-term utility savings over a standard non-condensing model. The Rinnai RU160eN features a UEF of 0.95, while the Rinnai RU180iP offers a UEF of 0.102. Because the Rinnai RU160eN uses condensing technology to capture waste heat, it provides significant energy savings over older, less efficient models. You should confirm the specific UEF with your local utility provider to calculate the exact payback period on the higher upfront cost of condensing units. Note that professional installation is required for these systems, and costs for gas line upgrades or permits can often equal the price of the unit itself.

Maximum Flow Rate

Maximum flow rate dictates how many fixtures you can run simultaneously without a drop in temperature. You need a flow rate of at least 3.5 GPM for a standard shower, but 10 GPM is the threshold for running two showers and a sink at once. The Rinnai RU180iP leads the group with a 10 GPM flow rate, while the Rinnai RU160eN provides 9 GPM. The Noritz NRC66DVNG offers a lower 6.6 GPM, which may limit simultaneous use in larger households. If you plan to run multiple high-flow fixtures, the Rinnai RU180iP’s 10 GPM capacity separates the field from the other options we compared.

Ventilation Requirements

Ventilation requirements are determined by whether the unit is an indoor or outdoor installation and its condensing status. You must verify your local building codes for venting before ordering, as condensing units often require specific materials like Schedule 40 PVC Pipe and Fitting. The Noritz NRC66DVNG is designed for indoor use and includes a 6′ power cord. The Rinnai RU180iP is also an indoor model, whereas the Rinnai RU160eN is designed for outdoor installation. Because these are condensing units, the venting setup is more complex than standard models; always hire a qualified installer to ensure the exhaust meets safety standards and local permits.

Noise Level Decibels

Noise level decibels affect the acoustic comfort of your home, especially when the unit is located near living spaces. While specific decibel ratings were not provided in the data for these models, indoor units like the Rinnai RU180iP and Noritz NRC66DVNG are generally quieter than outdoor units. If you are installing a unit near a bedroom, prioritize an indoor model. You should ask the installer to confirm the decibel output of the specific model during the installation process to ensure it meets your requirements.

What You Need vs What These Picks Deliver

Match the job you actually need done to what it requires, then check whether anything on this page reaches that level. Where nothing does, the row says so.

Thresholds are the levels this category is generally held to, not manufacturer claims. Check them against your own workload before buying.

Who Buys Tankless Water Heater Installations, and What It Really Costs

Buying Questions Answered

Does my home have the proper venting requirements for a condensing unit?

Condensing units like the Rinnai RU180iP and Noritz NRC66DVNG require specific PVC venting rather than the traditional stainless steel used for non-condensing models. You must confirm with a qualified installer that your current venting layout can accommodate these specific PVC standards to ensure the unit operates safely and meets local building codes.

Will this unit handle the high-pressure requirements of a high-flow showerhead?

High-flow showerheads require a consistent supply that meets a 3.5 GPM threshold to prevent the water from turning cold mid-use. The Rinnai RU180iP provides a hot water flow rate up to 10 GPM, which exceeds the 3.5 GPM requirement for standard high-flow fixtures. If your specific showerhead requires more than 10 GPM, you must verify the maximum flow rate with the fixture manufacturer before purchasing.

Which condensing tankless hot water heater should I buy for a high-volume household?

You should choose a model with a high flow rate if you need to run multiple fixtures simultaneously. The Rinnai RU180iP offers a 10 GPM flow rate and can accommodate up to 6 appliances at once for $1,336.

Is the Noritz NRC66DVNG worth it for a budget-conscious upgrade?

You may prefer a lower entry point if your household does not require maximum flow rates. The Noritz NRC66DVNG provides a 6.6 GPM flow rate and a remote thermostat for $489.99.

Understanding your options is easier when you learn about the different types of tankless water heaters.

Who Should Skip These Tankless Water Heater Installations

Buyers often select a unit that cannot handle the simultaneous demand of multiple fixtures, resulting in a flow rate shortfall and cold water mid-shower. You should confirm your peak demand requirements before ordering, as these models are limited to a maximum of 10 GPM.

If you require a flow rate of 15 GPM to support a high-volume commercial-scale operation, none of the models on this page reach that threshold. These units are designed for residential applications and do not meet the demands of high-volume commercial environments.

For high-volume commercial needs, you should look for multi-unit commercial systems. If you need to evaluate different residential setups, see best tankless hot water heater for high flow (up to 11 GPM).