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Does a Gas Furnace Dry Out the Air in a House?

burners-in-furnaceThis is a question we often hear, because it’s almost conventional wisdom that a gas furnace makes the air inside a home drier during winter. But conventional wisdom isn’t always correct, and false information spreads fast today.

So let’s confront the question here: Does a gas furnace really dry out the air in a house? If it does, that’s a major concern because dry air in winter can create comfort problems and even health issues.

A Gas Furnace Doesn’t Directly Dry Out the Air in a House

That would seem to be the end of it, right? 

Well not entirely. But the core fact to know is that the basic action of using gas burners in a furnace to heat the air does not make the air drier. The way a furnace works is to send heated combustion gases into a metal chamber (the heat exchanger), which then heats the surface of the exchanger. Air from the blower moves around the exchanger and picks up heat from the metal. At no point does it come into contact with the burners, and there’s no loss of moisture through this process. 

But a Gas Furnace Can Contribute to Drier Conditions

Now it sounds like we’re going back on what we just said. The issue is not that the furnace heating the air is drying it. It’s where the furnace draws air for combustion.

As you probably know from basic safety lessons, fire requires oxygen to burn. The burners need to draw air to ignite and burn. In standard older furnaces, called atmospheric furnaces, the air for the combustion process is drawn from the air surrounding the furnace—the burners are open to the outside. You can tell you have an atmospheric furnace if you can look inside and see the flames of the burners.

When the furnace draws on air from the house, it leaves an air deficit indoors. This causes an influx of air from outside the house to push indoors. Because the air outside is drier during winter, this movement of air indoor will cause a drop in humidity levels. This where the “gas furnaces dry the air” idea comes from.

Enter the Sealed Combustion Furnace

Now we come to the good news: newer furnaces with sealed combustion. In this type of furnace, the combustion chamber is sealed from the house; you can’t look into this furnace and see the flames. The furnace draws air through a PVC pipe that leads to the outside of the house so it doesn’t create any air deficit in the house. Sealed combustion has several other advantages, such as improved energy efficiency and safety. If you are looking into replacing your old furnaces, we recommend considering a sealed combustion furnace. 

No matter if you’re ready for a new furnace or you only need furnace repair in Burlington, VT, we’re the local pros to help you. We can also see problems with excessively dry air and offer solutions. 

Red Rock Mechanical, LLC serves Northwest Vermont and Northeast New York. Speak to us to find out how to get the best heating comfort for your home.

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