What to Know About Water Heaters and Backdrafting

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When we initially hear about backdrafting, we might think about fires and explosions. Backdrafting regarding water heaters may not be as dramatic as movie production, but the concept is similar. So, let’s look at what backdrafting is concerning water heaters and why it is essential to know about it.

What is Backdrafting?

Backdrafting is when the exhaust gases from your water heater, rather than safely leaving the house via the vent, spill back into your house. These exhaust gases contain carbon monoxide and moisture. This action is considered dangerous and should be rectified as soon as the homeowner discovers it. Due to the carbon monoxide component, it is always a good idea to set up a carbon monoxide detector near your water heater for safety.

5 Physical Signs That Your Water Heater May Be Backdrafting

Even before testing your water heater for backdrafting, there are some physical signs that you might notice that will alert you to this dangerous situation, including:

  • Melted plastic
  • Corrosion
  • Moisture
  • Wet cold-water pipes
  • Poorly pitched vent connector

Melted plastic at the draft hood – If you notice that the plastic on the top of your water heater is melted, you are pretty much guaranteed to find that your water heater is backdrafting. There are a couple of other reasons that the plastic might be melted, but the chances of it being one of those pale in comparison to the possibility of it being backdrafting.

Corrosion on top of your water heater – If you discover corrosion on top of your water heater, there is a good chance that your water heater is backdrafting. The exhaust gases will form condensation on top of the water heater and begin to corrode the top of the tank. You can quickly tell the difference between this and possible corrosion from a leaking shutoff valve because a leaking shutoff valve would have corrosion directly beneath the valve.

Condensation on tank top – If you see condensation on the tank top, you’re watching the water heater backdraft in action.

Excessive condensation on cold-water pipes – If you walk into your water heater room and notice excessive condensation on your cold-water pipes, this can be thanks to your backdrafting water heater. Even when they have condensation that’s due to warm weather, a backdrafting water heater will make them much worse. 

Improperly installed vent connector – When you installed your water heater, the connector should have been placed at an upward pitch. Additionally, it should have been installed with no quick turns, particularly at the draft hood. If it wasn’t installed this way, there might be a problem with the water heater and backdrafting.

How Do You Test Your Water Heater For Backdrafting?

One of the simplest ways to check to see if a water heater is backdrafting is by simply taking a small mirror or glass and holding it up to the draft hood – if backdraft is occurring, the glass or mirror will fog up. You can also use a lighter or matchstick. Then, if there is any draft within the vents, you will see the flame being pulled in. 

Another test method is to put powder into the draft diverter. Then, if it spills back into the room, you will know that your water heater is likely backdrafting.

However, if you want to verify for sure whether your water heater is backdrafting, here is the gold standard method for testing:

  • Turn the heat down at the furnace or boiler (only if they share a vent)
  • Close all windows and doors
  • If there are any fireplace dampers, close them
  • Turn on all exhaust fans in the kitchen and bathroom
  • Turn on clothes dryer if there is one
  • Run hot water in bathtub or laundry sink to get water heater to kick on

This will create a “worst-case scenario” for your water heater, but if it has been installed properly, it should still perform correctly and not backdraft. Before you test it, let it run for a short period. Sometimes, under this amount of stress, it may initially backdraft for a couple of minutes, but it will draft properly once the vent connector warms up.

Once a few minutes have passed, you can cup your hands around the draft hood without actually touching it. If the water heater is backdrafting, you will feel the warm, moist air escaping from the draft hood. If you want visual confirmation, you can take the small mirror or glass and hold it up to see if it gets fogged up from the warm air.

What Causes Backdrafting?

  • Poor vent installation
  • Vent obstructions 

Problems with vent connectors – When installing a water heater, the vent connector is the piece that takes the exhaust gases from the draft hood to the vent. If this piece isn’t installed correctly, the potential for backdraft increases.

The most common error seen with this is improper pitch. This is when the pitch isn’t done upward but rather flat or downward. There needs to be a minimum of ¼” per foot rise. Additionally, there cannot be a quick 90-degree turn right at the draft hood.

Another common error is when there is too long of a horizontal run, and the exhaust fan doesn’t have the power to push the exhaust gases the length of it. Gas codes recommend that the vent connector be as short as possible to alleviate this possibility.

Obstructed chimney or vent – Whether it is a squirrel, rocks, leaves, or branches, any obstruction in a chimney or vent will make the water heater vulnerable to backdrafting. To prevent this eventuality, it is recommended that a listed cap should be installed on top of the chimney. This will prevent debris from falling into the vent, keep the rain out, and prevent downdrafts during intense outdoor wind events.

Backdrafting can be a life-threatening issue when it occurs with your water heater. Knowing how to check your water heater for this issue can save your and your family’s lives. Contact Lloyd Industries, trusted specialists for the past 35 years, for expert advice. From fire dampers to brick vents, we carry everything you might need. If you are looking for a local HVAC tech, refer to our vetted list of experts in your area!