Navien Tankless Water Heater Not Saving Gas? 8 Reasons Why & How To

ByDavid Clark

You made a smart investment in a high-efficiency Navien tankless water heater, dreaming of endless hot water and, more importantly, a much friendlier gas bill. But now you’re looking at your monthly statement, and the numbers just don’t add up. If you’re finding your navien tankless water heater not saving gas like you expected, you’ve come to the right place.

Don’t worry—this is a situation we see often in the field, and it’s usually caused by a handful of correctable issues. As an HVACR technician, I’m here to tell you that the problem isn’t always the unit itself. It’s often a combination of usage habits, installation details, and simple maintenance that gets overlooked.

I promise to help you get to the bottom of it. We’re going to walk through the most common reasons your Navien might be underperforming and what you can do about it.

In this complete navien tankless water heater not saving gas guide, we’ll cover everything from simple setting adjustments and household habits to critical installation checks and essential maintenance. You’ll learn how to diagnose the issue and unlock the energy savings you were promised.

Understanding How Navien Heaters *Should* Save Gas

Before we dive into troubleshooting, let’s quickly touch on why tankless heaters are designed to be so efficient. Unlike a traditional tank-style heater that constantly burns gas to keep 40 or 50 gallons of water hot 24/7, your Navien is an “on-demand” unit.

It only fires up its powerful gas burner when you turn on a hot water tap. This fundamental difference is the primary source of savings. High-efficiency condensing units like Navien’s NPE series take it a step further by capturing and reusing heat from the exhaust gas that would normally be wasted, pushing their Uniform Energy Factor (UEF) rating well above 0.90 (meaning over 90% of the fuel is converted to heat for your water).

However, this efficiency depends on the unit operating under the right conditions. If those conditions aren’t met, the savings can quickly disappear.

Common Problems: Usage Habits & Household Factors

Often, the reason a navien tankless water heater not saving gas has more to do with us than the unit itself. Let’s look at some common household habits that can secretly drive up your gas consumption.

H3: The “Cold Water Sandwich” and Frequent, Short Draws

Do you often turn the hot water on for just a few seconds to rinse a dish or wash your hands? Every time you do this, the Navien unit fires up, burns gas to heat a small amount of water in its heat exchanger, and then shuts down. Most of that heated water never even reaches your faucet.

This frequent start-and-stop cycle is highly inefficient. It’s like starting your car just to move it ten feet. Grouping your hot water uses together can make a significant difference.

H3: A Sudden Increase in Hot Water Demand

Did your household change recently? A new family member, a teenager who loves long showers, or even a new high-volume appliance like a soaking tub can dramatically increase your hot water demand. The unit is simply working more to meet this new demand, which naturally means it will use more gas.

H3: Your Temperature Setting is Too High

We often see units set to 140°F, forcing homeowners to mix in a lot of cold water at the tap to get a comfortable temperature. This is incredibly wasteful. You’re paying to superheat water, only to immediately cool it down.

For most households, a setting of 120°F is perfectly safe and sufficient. Lowering the setpoint means the heater doesn’t have to work as hard, saving a surprising amount of gas over time.

Installation Quirks: The Hidden Gas Guzzlers

A flawless installation is non-negotiable for tankless efficiency. Unfortunately, not all installations are created equal. If your unit has been guzzling gas from day one, the issue might trace back to its initial setup.

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H3: Improper Gas Line Sizing

This is the number one installation mistake we find. A tankless water heater needs a much larger volume of gas, delivered instantly, than a tank-style heater. If the gas pipe feeding the unit is too small (e.g., a 1/2-inch line when a 3/4-inch line is required), the unit will be starved for fuel. It may run longer or struggle to maintain temperature, destroying its efficiency.

Pro Tip: Check your Navien’s installation manual for the required gas pipe size based on its BTU rating and the distance from the meter. If you suspect an issue, this is a job for a licensed plumber or gas fitter. Never attempt to work on gas lines yourself.

H3: Incorrect Venting Configuration

Navien condensing units require specific venting materials (like PVC, CPVC, or polypropylene) and must be installed with the correct length and pitch. Improper venting can restrict airflow, leading to poor combustion. Inefficient combustion means you’re not getting all the heat you’re paying for out of your natural gas or propane.

H3: Hot/Cold Water Crossover

A “crossover” is a sneaky plumbing issue where a faulty faucet, valve, or appliance allows cold water to leak into your hot water lines. When this happens, your Navien will sense a constant temperature drop and fire up repeatedly to reheat the water in the pipes, even when no one is using hot water. It’s a silent gas-waster that can be tricky to diagnose.

Your DIY Navien Tankless Water Heater Care Guide

Ready to take action? Here are a few safe checks and maintenance tasks you can perform to improve your unit’s efficiency. This is a great starting point for anyone looking for a practical navien tankless water heater not saving gas care guide.

  1. Lower Your Temperature Setting: Go to your unit’s control panel and lower the setpoint to 120°F. Live with it for a week. If the water is plenty hot for your needs, you’ve just found an instant, free way to save gas.
  2. Inspect for Leaks: Carefully check the plumbing around your water heater and look under sinks for any signs of a slow drip from a hot water line. Even a small leak can trigger the unit to fire unnecessarily.
  3. Listen to Your Unit: Get familiar with the normal sounds of your Navien firing up and running. If you start to hear new noises like rumbling, kettling, or banging, it could be a sign of scale buildup inside the heat exchanger.
  4. Flush and Descale Your Unit (Annually): This is the most important maintenance task for any tankless water heater, especially in areas with hard water. Mineral scale (calcium and magnesium) builds up on the inside of the heat exchanger, acting like insulation. This forces the unit to burn more gas for longer to transfer heat to the water. You can find DIY descaling kits online, and the process involves circulating a vinegar or approved descaling solution through the unit for about 45-60 minutes. Always follow the manufacturer’s instructions and turn off the power and gas to the unit before starting.

Eco-Friendly Navien Best Practices for Maximum Savings

Once you’ve ruled out problems, you can focus on optimization. Adopting these sustainable navien tankless water heater not saving gas best practices will help you get the most out of your high-tech appliance.

H3: Master Your Recirculation Settings

Many Navien models (like the NPE-A2 series) have a built-in recirculation pump. This feature is designed to eliminate the wait for hot water at the faucet, but it can use extra gas if configured improperly. Your unit likely has a few modes:

  • Intelligent Pre-heating: This “smart” mode learns your hot water usage patterns and only recirculates water when it anticipates you’ll need it. This is often the most efficient setting.
  • Scheduled Recirculation: You can set specific times for the pump to run (e.g., in the morning before work).
  • Always-On (DHW Recirculation): This mode keeps the hot water loop warm 24/7. It provides instant hot water but is the least energy-efficient option and can significantly increase gas usage.
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Check your settings and switch to the “Intelligent” mode for a better balance of comfort and efficiency.

H3: Pair with Low-Flow Fixtures

An easy way to use less hot water is to install WaterSense-certified low-flow showerheads and faucet aerators. By reducing the volume of water you use, you naturally reduce the amount of work your Navien has to do, directly cutting down on gas consumption. This is a key part of an eco-friendly navien tankless water heater not saving gas strategy.

When to Call a Navien-Certified Technician

While there’s a lot you can check yourself, some issues absolutely require a professional. Your safety is paramount. Call a qualified, Navien-certified technician if:

  • You smell gas near the unit. Leave the area immediately and call your gas company’s emergency line from a safe distance.
  • The unit is displaying an error code on its screen.
  • You suspect the gas line is undersized or there’s a venting problem.
  • You are not comfortable performing the annual descaling maintenance.
  • You’ve tried all the DIY tips above and your gas bill is still unusually high.

Frequently Asked Questions About Navien Gas Consumption

How much gas should a Navien tankless water heater use?

This varies widely based on groundwater temperature, household size, usage habits, and local gas prices. A better approach is to compare your gas bills month-over-month and year-over-year. A properly functioning unit should lead to a noticeable (typically 15-30%) reduction in the portion of your gas bill attributed to water heating compared to an old tank-style heater.

Does the recirculation feature use a lot of extra gas?

Yes, it can. The recirculation pump itself uses very little electricity, but the process of keeping the water in your pipes hot causes the burner to fire more often. Using the “Intelligent” or scheduled mode instead of the “Always-On” mode is one of the most effective navien tankless water heater not saving gas tips to manage this.

Can a small gas leak cause a high bill without me smelling it?

It’s possible, but less common for a leak to be large enough to spike a bill without being detectable by smell (mercaptan is added to natural gas for this reason). However, any suspected gas leak is an emergency. If you’re concerned, have your gas lines professionally inspected and pressure-tested.

Tackling a high gas bill can be frustrating, but by methodically working through these steps, you can identify the culprit. Your Navien tankless heater is a sophisticated piece of equipment capable of incredible efficiency—it just needs the right environment and a little care to deliver those savings.

You now have a solid checklist to diagnose why your navien tankless water heater not saving gas. From simple habit changes to essential maintenance, you’re empowered to take control of your energy bills. Stay safe, stay efficient, and enjoy that endless hot water!

David Clark
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