How To Increase Water Output Navien Tankless Water Heater - A Pro'S

You invested in a high-efficiency Navien tankless water heater, dreaming of endless, powerful hot showers. But lately, it feels more like a frustrating trickle, especially when the dishwasher is running. Does this sound familiar? You’re not alone, and the good news is, you’re in the right place.

Low water output is one of the most common frustrations homeowners face with any tankless system. It often feels like the unit isn’t living up to its promise. But don’t worry—we promise to guide you through the exact reasons this happens and provide a clear, step-by-step plan to fix it.

In this complete how to increase water output navien tankless water heater guide, we’ll walk you through everything from simple, 5-minute DIY checks to understanding the core mechanics of your system. You’ll learn how to identify the true culprit behind weak flow and restore that satisfying, high-pressure hot water you expect. Let’s get that flow back!

Understanding GPM and Temperature Rise: The Tankless Balancing Act

Before we touch a single valve or filter, it’s crucial to understand the two principles that govern your Navien’s performance: GPM and Temperature Rise. Think of them as two ends of a seesaw. When one goes up, the other often has to come down.

What is GPM (Gallons Per Minute)?

GPM is simply a measure of flow rate—how many gallons of water can move through your pipes and fixtures in one minute. Your Navien unit has a maximum GPM rating, which represents its total heating capacity. For example, a popular Navien NPE-240A2 model can produce up to 11.1 GPM, but that number comes with a big “if.”

The Critical Role of Temperature Rise

That “if” is the temperature rise. This is the amount of work your heater has to do to bring cold groundwater up to your desired hot water temperature. If your groundwater is 50°F and you set your heater to 120°F, the required temperature rise is 70°F.

Here’s the key takeaway: The higher the temperature rise, the lower the maximum GPM your unit can deliver. In the winter, when groundwater is much colder, your Navien has to work harder, which naturally reduces the hot water output. This isn’t a flaw; it’s the physics of heating water on demand.

Your First Line of Defense: Simple DIY Checks to Boost Water Output

Now for the hands-on part. Many flow issues aren’t caused by a major heater malfunction but by simple blockages. Before you even think about calling for service, run through these checks. These are the foundational how to increase water output navien tankless water heater tips every owner should know.

1. Clean the Inlet Water Filter Screen

This is the number one cause of gradually decreasing water flow. A small screen on the cold water inlet pipe catches sediment and debris before it can enter your heater. Over time, it gets clogged.

Turn Off the Power and Water: Shut off the electrical power to the unit and close the main cold water inlet valve (usually with a blue handle).
Relieve Pressure: Open a nearby hot water tap to relieve any pressure in the lines.
Locate and Remove the Filter: Unscrew the cold water line from the bottom of the unit. Just inside the inlet, you’ll see a small, thimble-shaped filter. Gently pull it out with needle-nose pliers.
Clean and Reinstall: Rinse the filter thoroughly under a faucet until it’s clean. You can use an old toothbrush to gently scrub away stubborn buildup. Reinsert the filter and reconnect the water line, ensuring it’s snug.

Turn the water and power back on and test the flow. You might be shocked at the difference this one small step makes.

2. Inspect and Clean Faucet Aerators and Showerheads

Sometimes the problem isn’t the heater at all, but the fixtures themselves! Mineral deposits (scale) can easily clog the small holes in your aerators and showerheads, severely restricting flow.

Unscrew the aerator from your kitchen or bathroom faucet and the head from your shower arm. Soak them in a bowl of white vinegar for a few hours to dissolve the mineral buildup, then scrub them with a brush and rinse. This is a simple but highly effective trick.

3. Verify Your Gas Supply is Fully Open

Your Navien needs a strong, steady supply of natural gas or propane to heat water effectively. Find the gas shutoff valve on the line leading to your heater (it usually has a yellow or red handle). Ensure the handle is parallel to the pipe, which indicates it’s fully open. If it was partially closed, it could have been starving the unit of the fuel it needs to perform under high demand.

How to Increase Water Output Navien Tankless Water Heater: Advanced Solutions

If the simple checks didn’t solve the problem, it’s time to look at deeper maintenance and system-level issues. This section explores the more involved solutions that get to the heart of the common problems with how to increase water output navien tankless water heater performance.

Descaling the Heat Exchanger (The Hard Water Culprit)

If you live in an area with hard water, limescale is your heater’s worst enemy. Over months and years, mineral deposits build up on the inside of the heat exchanger, acting like cholesterol in an artery. This buildup not only restricts water flow but also forces your unit to work harder, reducing its efficiency and lifespan.

Descaling involves circulating a cleaning solution (like diluted vinegar or a commercial descaling product) through the unit using a small pump and hoses. While some experienced DIYers tackle this, we strongly recommend hiring a qualified technician. An improper descaling can damage the unit. Regular descaling is a cornerstone of any good how to increase water output navien tankless water heater care guide.

Is Your Unit Undersized for Your Home?

This is a tough pill to swallow, but sometimes the unit is simply not powerful enough for your home’s needs. If the heater was installed without a proper calculation of your peak hot water demand (e.g., two showers, the dishwasher, and a washing machine running simultaneously), it may be undersized.

If you notice significant flow drops every time multiple fixtures are used, especially in winter, your unit’s maximum GPM at your region’s temperature rise may be too low. A professional can help you calculate your demand and determine if you need a larger model or a second unit installed in parallel.

Optimizing Your Plumbing System for Maximum Flow

Sometimes the Navien unit is working perfectly, but your home’s plumbing is the real bottleneck. Expanding your view to the entire system can unlock significant performance gains and deliver the true benefits of how to increase water output navien tankless water heater technology.

The Impact of Pipe Diameter

Tankless water heaters, including Navien models, typically require a 3/4-inch pipe for both the hot and cold water lines. If your home was plumbed with older 1/2-inch pipes, the sheer volume of water that can be delivered to and from the heater is physically limited, creating a permanent bottleneck regardless of the heater’s capacity.

Consider a Recirculation Pump

Does it take forever for hot water to reach your furthest bathroom? A recirculation system, like Navien’s own NaviCirc™, can solve this. It slowly circulates hot water through your pipes, so it’s instantly available at the tap. While it doesn’t increase the heater’s max GPM, it dramatically improves the perception of flow by eliminating the long, wasteful wait for hot water.

Sustainable and Eco-Friendly Best Practices for Your Navien Heater

A high-efficiency Navien heater is already a great choice for the environment. Following sustainable how to increase water output navien tankless water heater practices ensures you get maximum performance with minimum impact.

An eco-friendly how to increase water output navien tankless water heater strategy starts with maintenance. A clean, well-maintained unit uses less gas to heat the same amount of water. Regular descaling and filter cleaning aren’t just for performance; they’re for efficiency.

Additionally, set your water temperature to a safe and efficient 120°F. Higher settings waste energy and increase the risk of scalding. Fixing flow issues also prevents the wasteful habit of running taps longer just to get adequate pressure, saving both water and energy.

Frequently Asked Questions About Increasing Navien Water Output

Why does my Navien water flow decrease in the winter?

This is due to the “temperature rise” we discussed. The incoming groundwater is much colder in the winter, so your heater has to work significantly harder to heat it to your set temperature. This increased workload reduces the maximum gallons per minute (GPM) the unit can produce, resulting in lower flow at the tap.

Can I increase the GPM setting on my Navien unit myself?

No, the GPM is not a user-adjustable setting. It is a physical limitation based on the model’s burner size and the laws of thermodynamics. You can adjust the output temperature, but the maximum flow rate is determined by the unit’s capacity and the temperature rise required.

How often should I descale my Navien tankless water heater?

This depends entirely on your local water hardness. In areas with soft water, you may only need to do it every 3-5 years. In areas with very hard water, it should be done annually as preventative maintenance. A technician can test your water and recommend the ideal schedule.

Will a water softener help increase the output of my tankless water heater?

A water softener will not directly increase the GPM, but it is one of the best long-term investments for a tankless system. By preventing limescale buildup from ever forming in the heat exchanger, it ensures your unit maintains its factory-rated flow and efficiency for its entire lifespan. It’s a preventative measure that avoids future flow restrictions.

By following this guide, you now have the knowledge to diagnose and address the most common causes of low water output from your Navien tankless water heater. Start with the simple DIY checks, commit to a regular maintenance schedule, and don’t hesitate to consult a professional for more complex issues.

Restoring that powerful hot water flow is within reach. Here’s to powerful showers and the on-demand comfort you deserve. Stay safe and enjoy your endless hot water!

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David Clark

Founder & Lead HVAC Specialist at HVACRLY

David Clark is the founder of HVACrly and a certified HVAC specialist with 10+ years working on residential and light-commercial systems. He turns complex heating, cooling, ventilation, and refrigeration topics into clear, actionable guides focused on safety and energy efficiency. When he’s not on a service call, he’s testing tools and writing step-by-step tutorials.