Learn how condensation in venting is generated, what causes it, how it affects your gas water heater, and how to prevent or fix it.
Condensation occurs when water vapor is chilled below the dew point (the temperature at which water in a gaseous state turns into liquid).
Condensate is often seen on the outside surface of the glass filled with cold water on a hot day. Or, while the colder water passes through the pipe when exposed to the warm air.
In water heating systems, condensate appears when a new water heater is filled with cold water for the first time or when using large amounts of hot water in a short time, and the incoming water is cold. It is common in undersized water heaters, in the winter and early spring, when the incoming water is the coldest.
In power vent water heaters, condensation happens when the hot flue gases and moisture it carries come in contact with hot surfaces.
A water heater can produce approximately half a gallon of water vapor every hour of operation. This is especially noticeable in high-efficient water heaters that operate with lower temperatures of flue gases.
Condensate is frequently mistaken for leaking because a puddle of water can be found on the floor and surrounding the heater shortly after being used. Once the water heater reaches a temperature around 120 F, the condensation should stop.
Due to the acidic nature, condensation is something to avoid in power vent water heaters, and most of the time is the result of a piping configuration and environmental conditions.
Most typical installations of gas water heaters do not require any special methods for condensate disposal. This includes installations in the basements, garage, inside the home, and piping through the wall, attic, and where the pipes are short.
We will explore two scenarios of how venting pipes are installed and their effect on condensation; horizontal vent installation through the outside wall and vertical through the roof.
In horizontal vent systems, the vent pipe can slope away or toward the water heater. If the vent pipe slopes away, the drain port cap located where the pipe exits the water heater (blower pipe coupling) should stay in place, and the slope has to have at least 1/8 inch per foot. This is the recommended setup, but if it is not feasible, then the vent pipe will slope toward the water heater, so condensate collection and disposal must be provided. This is how:
Locate the blower pipe coupling at the top of the heater and remove the drain port cap.
Connect one end of the flexible tube to the blower drain port. The tube should be long enough to provide proper drainage, has the correct inner diameter (usually ½”), and is made of silicone for flexibility.
Make the circular trap (P shape loop) about 12” below the top of the unit and secure it with the zip ties to prevent the loop from unfolding. The loop must be smooth, with no restrictions or kinks; it must provide free condensate drainage.
The loop must be filled with water to prevent combustion gases leaks into the room.
Direct the other end of the silicone drain tube to the floor drain or outside the house.
In the case of the vertical venting, take the same action steps as described in the previous scenario, with the unplugged drain port and proper drainage via a silicone tube. Keep in mind that all horizontal sections must slope toward the water heater at 1/8” per foot.
Condensation in gas water heaters is not dangerous but can cause problems.
During condensation, water drops that form on the flue tube may fall onto the burner and other hot surfaces, producing a "sizzling" noise.
In the case of excessive condensation inside the vent tubes, water can drop not only on the burner but the pilot light as well, causing pilot outages.
As we can see, normal condensation is expected and is nothing to worry about, but when it happens in an excessive amount, it can be a problem, so you better call a professional to check your water heater.