Winter odor

[Andrew G]

Every year when it starts to get colder, we get this strong smell in the house like a sewer problem.

Before we can find out where it's coming from, the smell goes away.

It never happens in the summer or spring, just in the winter.

Have you ever heard of this, and if so, what can we do to fix it?

[home improvement guy]

You are not alone with this problem. In the past I've run across similar situations where the condensate drain from the furnace is connected directly to the home's sewer system. Inside the furnace is a cooling coil that collects moisture from the air inside the home. As the moisture condensates on the coil, it has to be drained to a collection point that is usually a sewer opening. If the plumber has installed a P-trap for the condensation drain, the heating technician can place the condensate drain hose inside the trap and everything should work as intended. Odors can become a problem if a P-trap has not been provided or if the open trap has been sealed with the condensate drain inside of it. I have even seen installations where a hole was drilled into the sewer pipe and the drain was connected directly to the sewer.

An acceptable installation would be to drain the condensate to a sewer at a P-trap opening as long as there is a one-inch air break between the two pipes. The break prevents the furnace fan from pulling sewer gases back through the dry drainpipe and into the air system of the home. This is why you only experience the odors in the winter when the air conditioner is off and the drainpipe is dry. Even if your condensate drain has an air break, there is a chance the P-trap could become dry through evaporation. Pouring a small amount of water in the open drain will establish a water seal in the bottom of the trap.