Instructions on How to Stop Water Heater Condensation (and Prevent)

During colder months, water heater condensation can be a frequent problem that homeowners encounter. It’s essential to understand that condensation is not a leak but rather a natural occurrence that happens when moisture forms on the surface of a water heater due to temperature differences between the tank and the surrounding air. This typically happens when the tank temperature decreases, and the humidity in the room is high.

(photo: Pixabay)

If left unchecked, the buildup of moisture from condensation can cause damage to the unit. To help homeowners identify, manage, and prevent condensation, our guide offers useful tips and tricks.

How Do I Tell if It’s a Water Heater Leak or Condensation?

Differentiating between a water heater leak and condensation can be challenging, but there are a few things to consider first.

When homeowners see a puddle of water under their water heater tank, they often wonder whether it’s a leak or just condensation. To clear up this confusion, it’s important to understand the following:

  1. What is condensation?
  2. Why it condensates in water heaters?
  3. Problems due to condensation and how to fix them
  4. Condensation vs. leaking – what is it?
  5. About condensing water heaters
  6. FAQ

What Is Water Heater Condensation?

Water heater condensation occurs when moisture in the air comes into contact with a cold surface, such as the outside of a water heater tank, and condenses into droplets of water. This is similar to how water droplets form on the outside of a cold glass on a hot summer day.

Gas water heaters produce a significant amount of moisture when natural or propane gas is burned. This can lead to water heater condensation when the water vapor is chilled below the dew point. The dew point is the temperature at which water vapor turns into liquid, known as condensate.

When the gas burner is on, the heater generates hot flue gases, which can turn into condensate upon contact with colder surfaces. One common scenario where condensation occurs is when the piping is cooled by the incoming water temperature.

The resulting moisture can lead to rust and corrosion on the tank, vents and other metal components, and may also cause damage to the surrounding area.

Why It Condensates in Water Heaters

To troubleshoot the water heater condensation, you have to recognize the symptoms first and which part of the unit condensates. Below are the main reasons for condensation:

  • Shortly after starting up a gas water heater and when the main burner is on, the heater will release condensate when it is filled with cold water.
  • Water heater condensation can occur when it is running for the first time.
  • You will also see a condensate after a long draw of hot water in a short time and when the refill water is very cold.
  • When the temperature setting is set too low, condensation might also occur. The solution is to increase the temperature.
  • An undersized heater is also the reason for more condensation, and even with a heater adequately sized, you can expect some condensation. The heater should be properly sized to meet your family’s demand for hot water, for for showers, dishwashing, and laundry.

Problems Due to Condensation and How to Fix Them

Common Problems

Excessive water heater condensation can be a cause for concern, as it can lead to several problems such as pilot light outage, premature corrosion of the burner area and the tank itself. This can be especially noticeable during the winter and early spring when the outside temperatures are at their lowest. The formation of small black or red granules on the main burner and top of the heater is a common sign of excessive condensation. These granules are caused by the buildup of soot and rust, which can lead to reduced heating efficiency and even pose a fire hazard in extreme cases.

Condensate typically contains hydrocarbons and carbonic acid, which can corrode a water heater over time. The areas of the heater most exposed to condensation are typically the flue tubes, baffles, and burners, which can be particularly vulnerable to rust and other forms of corrosion.

During operation, water heaters produce combustion products that contain moisture. When these products come into contact with the cooler surface of the tank, the moisture can condense and form water droplets. This can lead to dripping onto the burner or other hot surfaces, causing sizzling, frying, or popping noises within the burner area. For a visual example, you can refer to the video below.

Continual exposure to condensation can weaken the flue tube and other components of the water heater, potentially leading to corrosion and other forms of damage. In addition, excessive condensation can negatively impact gas combustion, potentially producing harmful byproducts like carbon monoxide.

Repair Tips

Here are some steps to fix water heater condensation:

  • Increase the temperature setting on the water heater to reduce the temperature differential between the tank and the surrounding air, which can help minimize condensation buildup.
  • Check for any leaks or damaged components that may be contributing to excessive condensation. Repair or replace any damaged parts as needed.
  • Install insulation around the tank to help maintain a consistent temperature and reduce the amount of moisture that forms on the tank’s surface.
  • Ensure that the water heater is properly vented to allow excess moisture to escape. A professional plumber or HVAC technician can help ensure that the venting system is working correctly.
  • Consider installing a dehumidifier in the room where the water heater is located to reduce humidity levels and minimize condensation buildup.
  • Regularly maintain the water heater by flushing it to remove sediment buildup, replacing the anode rod as needed, and checking for any other issues that may be contributing to excessive condensation.

The issue of water heater condensation may be mistaken for a leak due to the amount and suddenness of the condensate. However, it is typical for residential heaters to produce half a gallon of condensate per hour of operation, which usually dissipates after 1-2 hours of use.

Newer, high-efficiency water heaters and Energy Star models are more prone to condensation due to their use of powerful gas burners and advanced technology that extracts more heat from flues and flames.

To prevent damage to the surrounding area, it is recommended to install a suitable metal drain pan that is at least 2 inches wider than the water heater to collect any condensate.

How to Distinguish Between Water Heater Condensation and Leaking

Water heater condensation can be mistaken for a leak because they can have similar symptoms. However, there are a few ways to distinguish between the two:

  • Location: Condensation typically occurs at the bottom of the tank, while leaks can occur anywhere on the tank or in the surrounding pipes.
  • Amount of water: Condensation typically produces a small amount of water, while a leak produces a consistent flow of water.
  • Timeframe: Condensation usually appears after the first few minutes of operation and lasts for a short period, while leaks are consistent and do not stop.
  • Water quality: Condensation is typically clean water, while a leak may have rust, sediment, or debris in the water.

This is how you can also test it:

  • Make sure there is no water under the heater. If there is any, wipe it off.
  • Turn the thermostat on the gas control valve to the pilot position.
  • Wait for a few hours or one day, and check if any water is accumulated under the unit.
  • When the heater is heated above the temperature of 110 F, condensation should stop.
  • If there is no water under the heater, then you have condensation. If there is a puddle, check for leaking.

What About Condensing Water Heaters?

Condensing water heaters such as tank-type model Vertex from AO Smith, or tankless type from Rinnai, Noritz, or Navien, produce acidic condensate (pH level is 2-3) can cause corrosion or damages to the drain and sewer system. 

When you buy the neutralizer kit and install it on the heater, the condensate is treated adequately for safe disposal into the drain. The drain should be close to the unit; the pipe should provide a slope for the free flow or, if it is needed, have the condensate pump installed.

Ensure that the condensate flow is free and clear of debris and the drain does not allow backflow through the hose. If the condensate backups into the unit, an error code will flash, for example, a code “29” on the Noritz NRCP model. This is important, especially during the winter and freezing days.


Most water heaters experience some degree of condensation, which can be caused by issues with the unit or simply due to high levels of moisture in the air. It can be challenging to control moisture levels in a home, so it’s often best to accept a certain amount of condensation as normal. However, if you notice excessive condensation, it’s a good idea to contact a plumber. This type of condensation can cause a series of problems.


Is Water Heater Condensation Harmful and Should I Be Concerned?

Water heater condensation itself is not harmful, but it can lead to other problems such as rust and corrosion on the tank. It can also cause mold and mildew growth if the moisture is not properly ventilated. You should be concerned about condensation if it is excessive or if you notice any rust or corrosion on the tank. Excessive condensation can also indicate that the heater is not functioning properly and may require repairs or replacement.

How Much Condensation From a Water Heater Is Normal?

The amount of condensation from a water heater that is considered normal depends on various factors, such as the location, temperature, and humidity levels of the surrounding environment, as well as the age and condition of the unit. In general, a small amount of condensation on the tank’s surface is normal, especially during colder months. However, if you notice excessive amounts of condensation or if there is water pooling around the base of the tank, it may indicate a problem and require professional attention.

Why Is My Water Heater Flue Wet?

Water heater flue condensation occurs when water vapor in the exhaust gases produced by the water heater condenses on the interior surface of the flue vent pipe. Your water heater flue may condensate for several reasons, including improper venting, low exhaust temperature, high humidity, and cold outside temperatures. If it condensates excessively, this could be a sign of a more serious problem with your water heater, such as a malfunctioning or undersized venting system.

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