#AskDerekCole Episode 93
28 Jan 2026 · 4 min
Derek Cole answers questions about black material on HVAC filters, explaining it could be mold or soot, and recommends on-site inspection. He outlines pre-winter HVAC maintenance including cleaning coils and checking motors, capacitors, and boards.
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Hey, on this episode, we talk about black stuff on my filter and what should I be doing at this time of the year when summer's over? You ask your comfort and energy questions and they get answered. This is the Ask Derrick Cole Show. Hey, it's Derrick Cole. Welcome to episode 93 of the Ask Derrick Cole Show, Answering your home and energy questions. Coming off a great weekend, we had a team race. It was at the Spartan event. Spartan race. But we've raced as a team as well. So all of us, this is the scar to prove it. The bad thing is I thought this was mud when I went to the shower to wash it off, and I was like, ah, ah, it's not coming off. So that was not a good idea. Why is there black stuff on my filter? That is a very good question. We need to come check that out. It could be a number of things. Black stuff on the fil. I'm assuming you probably think it's mold or you would not be worried about it. But there's so many different types of mold. The thing about filters is that most of the filters you buy from the big box stores like Walmart, Home Depot, Lowe's, whatever. The filter is made out of a paper product. So the only reason mold and bacteria grow is when they have a food source. So paper is a food source. That's why you now have Sheetrock. That is, things can't grow on it because they don't make it out of paper anymore. So it says, like mold free or whatever they call it. It's because they don't have a food source. That's why when you have a metal duct system, mold and stuff cannot grow in that duct system. It's impossible. It's metal. There is no food for it to eat, so it cannot grow. So, yes, it could be that. And they can attach to it. And, you know, because it is a food source. I've seen before where people have a lot of candles in the house, a lot of soot happens, and that can cause black things to fly out of the grill or be stuck on the filter. So it could be a number of things, but bottom line is we need to come check it out, see what's going on, because black mist on the filter is not a good sign for anybody. So you need to see what's going on with that. What should I do to my system before it gets cold outside? We have come through a long, hot, humid summer, so the thing you need to do before it gets cold outside is you need to clean the system and check the system and get a maintenance done because it's at a long run time, from what like March, April to now, it's been running cooling. So in that period of time, you probably have not had a maintenance done. So you need to clean the coils, you need to check the motors, you need to check the amps on the motors, you need to check the capacitors and check the boards, make sure everything is good to go. So when you get that first 40 degree night or 30 degree night, you have heat in the home and something's not blowing out and not working. So after a long hot summer, the unit has run a marathon. You need to have it checked, serviced, cleaned by a professional to make sure it's all good to go. And yes, I know people say I can clean the coils myself. Yes, you can clean the coils yourself. But you need to go in that unit, you need to check all these readings for the capacitors and the motors and check the signals to the boards just to make sure everything is working properly. Because you don't want to be stuck on that first cold day of the year where everybody is calling in saying, I don't have heat, and then you're stuck in the same situation. So let's ignore an offense and on defense, let's go and get it checked out to make sure we're good to go. That's like two quick shows in a row, record time. I'm not repeating myself. Anyway, ask your questions and hashtag Amassderic Cole, Facebook, Twitter, Instagram, whatever you want to do or email me and we'll get them on the show.
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