Why is my cold air return blowing cold air while my furnace's running?

Probably because the blower is clearing the hot air

Hi Thomas,

Some thermostats have the ability to keep the thermostat running 24/7. That keeps the air moving and in theory it distributes the heat better. There should be a setting on your thermostat that will turn off that feature if you don't like it. We sold heating/cooling controls as part of a family business and this was started several years ago. I personally like it better when the 24/7 fan is turned off. I hope this helps you. Wishing you the best.

A return should not be blowing any air at all. A supply could blow cold air when the thermostat first calls for heat since it is clearing the line of the cold air that is in it before the hot air gets to the room. If you run your furnace fan all the time, you may have periods of time when there is cooler air coming from the vent since the thermostat is not calling for heat at that moment. The return air is supposed to be sucked into the return ducts to circulate the air in the room. Is is possible that there is no duct work in the wall. I would start by taking off the return cover and look for metal duct work in the wall. If there is no duct work, then the cold air could be coming from your attic or basement, particularly on a windy day. However, when we bought our home many years ago, we had a problem with neither vent blowing hot air. We did not have the house built, but we were the first owners. We took the vent covers off and looked into the wall. We had duct work in the wall. The company who installed the heating system never connected either vent to the trunk lines. The supply and return lines were in the garage ceiling and covered with sheet rock but not attached to the furnace. Basically the room had no heat. When we traced the duct work, we found that the garage ceiling had little insulation in it. The cold air was coming in from the garage. I hope this helps a little. Best of luck in your search for the breezy cold air!