An antifreeze smell from a furnace sounds like trouble, but it is not necessarily a problem. For boiler furnaces, an antifreeze smell can be an annual occurrence due to winterization procedures. Antifreeze is used in plumbing and furnace systems just as it is used in cars. But the odor can also indicate problems, including issues that are causing a separate smell that only mimics the smell of antifreeze.
Use of Antifreeze
In freezing winter months, antifreeze is used on hydronic heatings systems (which use an enclosed source of water) and outdoor furnaces to protect them from corrosion and freezing during periods when the system is not used, because frozen water can cause pipes to burst. Antifreeze should never be used in areas where it can leak into a water system you use for anything other than carrying heat. But its presence in the system can seep into other areas and lead to the smell.
Antifreeze and Leaks
Antifreeze is not the only thing that can cause an antifreeze odor. Another culprit may be the refrigerant in your system. While refrigerant is more often used in air conditioners, if you use a heat pump for heating, a refrigerant leak is a possibility. The refrigerant can give off the same odor and is usually accompanied by a lack of efficiency in your heating system.
Vent piping can also leak and cause odors. Sometimes sewer pipe vents can develop leaks and the smell can be confused with an antifreeze odor. However, if you use a hydronic water system and have added antifreeze to it, the smell can indicate a leak in this system that you should address. Antifreeze odors should not linger in a sealed system if you have not recently used the solution to winterize your heating. Some of your heating pipes may have sprung leaks near the furnace.
Rotten smells can sometimes resemble the smell of antifreeze, especially when combined with the burst dust smell that a furnace emits after not being used for some time. This is often an indication that some animal has died inside the furnace or its ductwork and needs to be cleaned out.