Summary: The heat exchanger coil in our HVAC system is where the magic of heat transfer happens - this is where the rubber meets the road when it comes to "conditioning" air. If the word "coil" is not connecting to a mental image, you can think of the radiator in your car. Just as in a car, when it's working you don't give your radiator much thought - we often ignore our HVAC coils, and at our peril. All of the indoor air we heat and cool flows through our HVAC coil. Unfortunately sometimes our magic, all-powerful coils are coated with a smelly, gelatinous, living glop in the form of an unwanted biofilm.
