Derek ColeGM, Simmons One Hour Heating & Air · AI HVAC Answers

What causes a mold smell when I turn my HVAC unit on

23 Apr 2018 · 2 min

Watch on YouTube

2:19

In this instructional video, Derek Cole explains that air‑conditioning removes heat by passing indoor air over a cold refrigerant coil, which inevitably creates condensation that drips into a drain pan. If the pan does not drain properly, the standing water creates a damp, dark environment where bacteria, mold, and other microbes can grow. This microbial growth is the source of the damp, musty, mold‑like odor that many people notice when they first turn on their HVAC system. Cole argues that the most effective way to stop this growth is to introduce ultraviolet (UV) light into the indoor coil area. He describes a “coil scrubber” that emits UV onto the coil, killing microbes and preventing odor. To illustrate the principle, he compares the UV coil scrubber to sunlight drying a wet mat: UV from the sun dries and disinfects the mat, just as UV inside the air handler eliminates microbial growth. The video concludes that adding UV light to the HVAC system replicates the sun’s natural disinfecting power, eliminating the musty smell.

Chapters

In air conditioning, you have to remove moisture to get humidity out of the air. So air conditioning is all about removing heat, right? So you're taking heat out of the air, it's going over a cold coil which has refrigerant in it, and then it's coming back out cooler air than what came in. So the byproduct of that is water. So that's why you have drain lines, that's why you see water dripping outside. So what will happen is when you have that hot air going across that cold coil, you get condensation, and that's going to drip drip down to the drain pan. Well, if that drain pan is not draining or something is the matter, things will start growing in that drain pan because you have cold water sitting in a damp, dark spot. So the thing that happens is growth, right? So even the most— the strongest bacteria in the world lasts 24 hours. So if it's not in the air or if it's a bug or it's a virus or whatever it is, it's going to die and it's going to sit at the bottom in that drain pan for a period of time. So you start getting— the first time you turn on your heat or your air conditioning, especially, you get that kind of damp, musty, moldy kind of smell. There's like all kinds of molds, so we don't call it mold, call it growth. So the way to prevent that from happening is to introduce UV into that system Somehow. Now we do it here with the coil scrubber, which shines on the indoor coil, has the UV power so nothing can grow in UV. If you want to prove that point, uh, everybody at home has that mat at the front or back of the house that has the mildew and it's kind of wet and it's kind of damp. Take that mat, stick it out in the middle of the yard in the sunshine for a period of time., and that will be clean and dry because nothing can grow when UV is present, right? So in the indoor air environment, in the air handler, that is not present. So we have to make it present with UV light. UV light will solve that problem. So the same power of the sun, the same energy that holds, we can bring into your system, and that'll stop that damp, dusty, musty smell.