A home's heat system will put off a different smell whenever you turn on the furnace for the first time in a few months. Smoke can indicate the presence of fire or other serious dangers, so if you smell smoke when your furnace is running, take the situation seriously and do all you can to find a quick resolution.
Since furnaces combust gas to create heat, which is then pushed through to the various rooms in the house, you need to proceed with caution if you smell any smoke while the furnace is operating. The smoke smell may indicate a deeper problem with the furnace that needs to be addressed by a service professional or even your gas utility company. If you see smoke coming out of the vents in the house or the furnace itself, you need to leave the house immediately and call for help.
Every time you start up the furnace after the warm summer months, you will smell an odor similar to smoke coming out of your heat vents. This smell comes from the furnace burning out the dust that entered it while the furnace sat idle. The burning smell generally subsides after an hour or so. If you clean the furnace off, especially the air vents, and change out the furnace filter before you start the furnace up for the first time, the smoke odor will last a shorter period of time.
Filter and Ducts
You need to change out a furnace's filter regularly to keep the furnace running properly. If your forget to change out the filter and it is fairly dirty, the smoke smell could be coming from the dirty and clogged filter. You do not change out the ducts in your house on a regular basis, but dirty ducts can also lead to the smoke odor. Hire an HVAC contractor to clean your ducts out if the smoke smell continues past the start of the cold weather season or if it starts suddenly after you have been using the furnace regularly for any period.
Closing enough of the heat vents in your house may seem like a good way to cut down on heating costs, but closing too many can lead to a buildup of warm air in the furnace. When you smell smoke coming out of the air vents, then is the time to count how many are open and how many are closed. If the closed vents make up 20 percent or more of the vents in the house, you need to open more of the vents so that the hot air will not build up in the furnace.
Service the Furnace
When you cannot determine the cause of the smoke smell coming from the furnace or the heat ducts, shut off the furnace and keep it off until you can have a furnace repair technician look at the furnace. The furnace may need to be lubricated, leading to the motor overheating and smoking. A professional can determine the source of the smoke.