You’ve had your furnace for a while, and each winter you don’t have any trouble getting comfortable when it’s running. That’s the way things are supposed to be.
Now, however, something is wrong. You don’t feel cozy, and you’re layering on blankets. Your favorite long-sleeve shirt isn’t keeping you warm enough, and other folks in the house are complaining that it’s too cold. “Why isn’t the furnace on?” they ask. And you tell them that it is, and they don’t believe you, but the thermostat is set to the normal temperature, and…
Oh no. The furnace isn’t working right! It’s running, you can feel warm air coming from the room vents, but it’s not enough. Why is it? What’s happening?