Sick House Found – Water Heater Problem

A Rusted-Out Water Heater Flue Connection

Another sick house found — and in this case the problem could have caused serious health and safety issues, possibly even death.

What was the problem? Improper venting of the water heater caused the flue to rust out. In a closet inside the home where the furnace and water heater are stored, there was a disconnected water heater flue that allowed combustion gases to vent directly into the home.

The broken connection pictured here is evidence that the water heater was not venting properly. Moisture condensed inside the flue and eventually rusted it out, creating an open path for combustion gases to move into the home. Not only could this allow gases to flow in from the water heater, but the hole in the furnace flue posed the same risk.

The most serious concern is carbon monoxide — silent, invisible, and odorless. But other harmful compounds can also pollute your home: nitrogen oxides, sulfur oxides, methane, VOCs, particulate matter, and other greenhouse gases.

This home was about 50 years old and had been purchased about 4 years ago. It was sold in this condition without anyone identifying the problem.

First Sign of Trouble: Negative Slope on the Flue

Looking at the water heater flue, it has a negative slope — meaning it tilts back toward the ground rather than upward. Flues on gas appliances must always slope upward so combustion gases can rise and exit the home. When a flue slopes the wrong way, gases have nowhere to go but back inside.

Second Sign of Trouble: Rust and Condensation

Rust stains and mineral deposits on and beneath the flue pipe are a clear indication that moisture vapor from combustion gases is condensing inside the pipe and leaking out. This kind of corrosion weakens the flue over time and eventually causes it to fail entirely.

Third Sign: The Hidden Connection

Above the furnace, where the furnace flue should connect with the water heater flue, the installation made the connection nearly impossible to see — and therefore easy to overlook. The vent into the attic at that same location could also cause problems if drafts push air into the attic and back into the home.

If you live in an older home and haven't had your venting system inspected, now is the time. A proper HVAC inspection can catch these issues before they become dangerous.