Water Heater Condensation and
How to Deal with It
(updated 2018)

Water heater condensation is not a leaking problem. Condensation is a normal occurrence when the gas water heating appliance is working. How to recognize condensation in water heaters, what to do, can it be stopped and how to troubleshoot problems?

What is the water heater condensation?

When natural or propane gas burns in gas water heaters, a lot of moisture in products of combustion is released. So when the water vapor is chilled below the dew point (link wiki), water heater condensation occurs. The dew point is the temperature at which water vapor turns into the liquid state, called condensate.

When the main gas burner is on, the heater produces hot flue gases, which turn into the condensate upon contacting colder surfaces. One of the situations where the condensation might happen is piping cooled by the low incoming water temperature that flows through.

Why it condensates in water heaters?

In order 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 the start-up, when the gas heater is filled with cold water, and the main burner is ON, the heater will release the condensate.
  • Water heater condensation is happening when dealing with the new heating appliances 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 occur also. 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 demand for hot water, for a shower, dishwashing and cloth washing.

Problems due to condensation and how to fix it

  • Excessive water heater condensation is not normal, but it may be noticed during the winter and in early spring when the outside temperatures are the lowest. This is what can cause the pilot light outage, premature corrosion of the burner area and the tank itself. Small black or red granules can be seen on the main burner and top of the heater.
  • Hydrocarbons and carbonic acid are found in the condensate, and they will corrode the heater. The most exposed parts to the condensation are flue tubes, baffles, and burners.
  • Moisture from the combustion products will condense on the cooler tank and form water drops, which may drip onto the burner or any other hot surface, resulting in the characteristic sizzling, frying or popping noise within the burner area.
  • Continual exposure to the condensation will weaken the flue tube. It can also affect the gas combustion by producing carbon monoxide.

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Because of the suddenness and the amount of condensate, this problem might be diagnosed as the leaking. Keep in mind that one half of the gallon of condensate during every hour of operation is typical for home heaters. It takes 1-2 hours for the tank to warm up so the condensation should disappear.

Since the new high efficient heaters and Energy Star models utilize the powerful gas burners; and combining it with the latest technology to extract even more heat from the flues and flames, they will condensate more than the older heaters that use less energy.

One of the solution when troubleshooting condensation in the heater is a good venting so the gas appliances will operate efficiently and vent the products of combustion together with the water vapor properly.

As the cooler flue gases are part of the reason for the condensation problem, the suggestion is to raise the supply air temperature, increase the stored water temperature or increase the size of the tank.

A suitable metal drain pan, at least 2" wider than the heater should be installed under the heater to collect the condensate and not to damage the area.

How to distinguish between condensation and leaking

  • 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, to check is there any water accumulated under the unit.
  • When the heater is heated above 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.

Condensing water heaters and condensate

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

By buying the neutralizer kit and installing it on the water 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 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 will not allow backflow through the hose. If the condensate backups into the water heater, an error code will flash, for example, a code "29" on Noritz NRCP model. This is important, especially during the winter and freezing days.


Almost all water heaters have some sort of condensation, if not due to improper unit work than due to an increased moisture in the air. And controlling the moisture is not an easy solution. In the case of normal condensation, it is better to accept the fact. I would call a plumber only if there is an excessive condensation as it might cause premature tank corrosion and corrosion of heating elements and contacts.

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