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Mold in the Airconditioner Ducts – 4 Signs to Watch Out For

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A mold infestation usually comes with health symptoms that are similar to respiratory allergies.

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At Thomas Hoffmann Air Conditioning & Heating, we pride ourselves on being a locally owned and operated HVAC company. With more than 30 years of experience and a master technician and mechanical engineer as our owner, we can replace, repair, and maintain your business or home’s HVAC system.

Of all the problems you might have with your air conditioning, mold in the duct system can be dangerous for your health and not so easy to get rid of. This problem develops over time and is not easy to identify before it gets too bad.

Teresa F.
2 days ago
Our service technician arrived right on time and was professional, friendly, efficient and courteous. We couldn’t ask for more.
Response from the owner:Thank you for sharing your positive experience with our service technician! We appreciate your kind words and are glad to hear that you were satisfied with the service provided.
Marilyn H.
6 days ago
Nick was was great! He provided great service, explained everything, and was patient and kind.I definitely recommend using Hoffman!
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Jasmine W.
7 days ago
The whole team was great, professional and friendly. Scheduling was easy and well organized, they had many options for different price points and financing options. Thank you!
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Henry D.
7 days ago
I have complete trust in Thomas Hoffman AC . I have had multiple
technicians who are always polite and knowledgeable.
Response from the owner:Thank you for your trust in our team, Henry! We appreciate your kind words about our technicians.
Theresa S.
2 weeks ago
Love that it’s the same technician every time. Let’s me know what he found and any concerns he might have regarding our units. Great customer service.
Response from the owner:Thank you, Theresa! We're glad to hear you appreciate having the same technician and the communication about your units. Your feedback on our customer service means a lot to us!
Frank P.
2 weeks ago
From the phone to the completion of the job everyone is so polite and informative. I had Giovani as our representative and he was very informative and professional, and knew exactly what the problem was. Thanks so much.
Response from the owner:Thank you for the kind review, Frank! We appreciate you and your business.
Allan G.
2 weeks ago
Zach did an excellent job! Always courteous and friendly. We would highly recommend calling Thomas Hoffmann HVAC for any heating and cooling needs.
Response from the owner:Thank you, Allan! We're glad to hear that Zach provided excellent service and appreciate your recommendation for Thomas Hoffmann HVAC.
William W.
2 weeks ago
Was able to locate the problem right away and replace a switch and add Freon very nice job by this employee. I will recommend Thomas Hoffman for future references.
Response from the owner:Thank you, William! We're glad to hear that our team was able to quickly address the issue and that you had a positive experience with Thomas. Your recommendation means a lot to us!
Jack D.
2 weeks ago
I had Nick come out. He was awesome. Very knowledgeable, prompt and helpful. I will definitely recommend Thomas Hoffmann HVAC to others in need of HVAC support.
Response from the owner:Thank you, Jack! We're glad to hear that Nick provided you with excellent service. We appreciate your recommendation and look forward to assisting you and others in the future.
FFE L.
2 weeks ago
From our initial quote until the new furnace and AC were completed, everything was smooth and efficient. Zachary and Giovanni were excellent on-site, taking time to explain the installation as well as leaving the home clean.
Thank you Thomas Hoffmann team
Response from the owner:Thank you! We're glad to hear that the installation process was smooth and efficient. Zachary and Giovanni will be pleased to know their efforts made a positive impact. We appreciate your kind words about the team!
Bob De P.
2 weeks ago
Courteous friendly and efficient! What else could you want!
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Princess C.
2 weeks ago
Update 4/6/26: Zach Sperling is such a pleasant and knowledgeable technician that I recommend him highly. Thomas Heating has been a wonderful company to work with in my maintenance plan. If you are looking for a reputable company, look no more.

This company is so responsive that I love them. They respond immediately, and I trust them to tell me what needs to be done. I haven’t been steered wrong yet. They are genuinely nice to work with and honest. I use their maintenance program which I highly recommend.
Response from the owner:Thank you for your kind words, we truly appreciate your trust in us and are glad to hear about your positive experience with our services.
Julie N.
3 weeks ago
So helpful! Straight into the point with no runaround or Negotiating up sells! Quick and efficient!
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George G.
3 weeks ago
Great fast courteous service, knowledgeable.
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harold B.
3 weeks ago
work good but got at least 6 messages from them
very annoying
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Philip D.
4 weeks ago
Nick was great! He came right out and was able to solve the problem fairly easily. He communicated well and helped us prevent a future problem as well.
Response from the owner:Thank you for the review, Philip! We are happy to hear you had a pleasant experience working with us.
Pat Keith T.
4 weeks ago
Geovanni is great!
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Greg D.
4 weeks ago
They have never failed to fix my hvac problems. These folks are top tier.
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Amy K.
1 month ago
Giovanni was very professional, helpful, patient and helped me figure out the issue, if it was covered under warranty, and next steps. Great overall experience and much appreciated.
Response from the owner:Thank you, Amy! We're glad to hear that Giovanni provided you with such professional and helpful service. Your appreciation means a lot to us!
Joe G.
1 month ago
Always professional and thorough whenever they service our home. We have used Thomas Hoffmann Air Conditioning & Heating multiple times since we moved into our home and will continue to use them in the future.
Response from the owner:Thank you for the thoughtful review, Joe. We appreciate you and your business!
Daniel D.
1 month ago
Met Nick at ACCA - conference for HVAC contractors. He’s an expert! 100%
14 years in the business, doing a great job and service.
Response from the owner:Hi Daniel! So happy to hear you enjoyed Nick's company. We are lucky to have him.
Kelly R.
1 month ago
Very easy to work with. Technician kept me informed about what was going on through the whole process.
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Jordan P.
2 months ago
Nick was awesome! He was extremely professional and answered any questions I had. Would highly recommend!
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Jill P.
2 months ago
Got the job done fast and explained every step as it was happening!
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Veronica V.
2 months ago
We have a tankless water heater that needed cleaning and a new part, they came out very quickly and got the hot water back again. Thank you!
Response from the owner:We are happy to hear you had a pleasant experience! Thank you for the kind review, and your continued support.
jay70001
3 months ago
0 stars if I could. Bought a faulty (not to mention overpriced) surface igniter, called back five minutes later after installing, of course they didn’t stand behind their part. Go to Grainger instead. Same (working) part, half the price.
Response from the owner:Hi there. I am unable to locate your customer profile. Please give our office a call at 314-471-7625 so we can get this figured out for you.
Katherine T.
3 months ago
Always a great experience. Was able to get out same day to help, knowledgeable of old homes, including their systems and new systems as well.
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April T.
3 months ago
My furnace was not working. A very nice gentleman came out this morning and fixed the problem and now I have much needed heat. He was very professional and courteous. I will definitely be using them again when the need arises.
Response from the owner:Thank you for the positive feedback! We're glad to hear that you were pleased with our prompt and friendly service. We look forward to assisting you again in the future!
Kathleen D.
3 months ago
Ryan was very professional, knowledgeable, and thorough. I was able to get an appointment the same day during a biter, snowy day.
Response from the owner:We are so glad to hear you had a pleasant experience, Kathleen!
Melinda D.
3 months ago
I will always call Hoffmans for my air and heat needs. They were out to my daughters house that day and fixed it. It was right before the weekend storm with below zero temps the next day. They saved my daughter and grandbabies. I could never thank them more.
Response from the owner:We are so happy to hear that we could help! Thank you for the kind review.
Scott S.
3 months ago
Snow and drifting snow covered intake and out take vents causing the furnace emergency to shut off furnace. Cleaned off the driftibg/ snow off roof and vents furnace works perfect now. Thank you and great job Nick.
Response from the owner:Thanks for the great review, Scott! We appreciate your support.
Jessica B.
3 months ago
Came during a storm with emergency call for heat- did a quick and fast job getting furnace running! Whoot!
Response from the owner:Thank you for the great review, Jessica! We appreciate your support.
Jennifer H.
3 months ago
5 stars! Nick was here to fix my heater within 2 hours of my call. He explained the problem to me thoroughly and got the job done quickly & professionally. Thank you so much!
Response from the owner:Thank you for the kind review, Jennifer! Glad we could help.
Matthew B.
3 months ago
Extremely thorough and educational. They do a wonderful job of explaining everything and making sure I was comfortable knowing how the systems worked in my house!
Response from the owner:Thanks for the great review, Matthew! We appreciate your support.
Joe C.
3 months ago
Nick did an amazing job, on time, very knowledge and professional.
Response from the owner:Thank you for the great review, Joe. We look forward to servicing you in the future!
anna M.
3 months ago
installed humidifier and hepa filter. Very pleased with service.
Response from the owner:We are happy to hear that you had a pleasant experience!
Abby C.
3 months ago
I noticed a strange noise that I was concerned was linked to my furnace. I called Thomas Hoffman Heating & Cooling and Nick came right out. He was very thorough checking all components. Thankfully all checked out for us this visit. Definitely recommend Thomas Hoffman Heating & Cooling!
Response from the owner:Thank you so much for the kind review, Abby! We appreciate your business and look forward to servicing you in the future.
DA O.
3 months ago
I would describe the overall experience as professional, but also kind and responsive from the initial phone call to the technician.
Response from the owner:Thank you for your kind review! We appreciate your business and look forward to helping you in the future.
Christine G.
3 months ago
Thomas Hoffman is a wonderful company to work with. Techs are knowledgeable, personable & efficient.
Response from the owner:Thank you, Christine, for your kind words about our team; we appreciate your feedback and are glad to hear you had a positive experience!

Here are four signs to look out for when regularly evaluating your air conditioning system. They will help you identify a mold problem early and solve it before it damages your health, home, or HVAC system.

Strange Smell in the House

The first sign usually noticed during a mold infestation is a strange, musky smell in the house, especially when the AC is on. The smell might be felt in the whole house or only in adjacent rooms that may get less sunlight or lack proper air circulation. The smell is similar to mildew smell, and you might become used to it over time. Ask someone who is visiting you if they notice a moldy smell when they enter your home. If you suspect something, call a professional AC service and have them check the inside of the vents.

Mold Spots or Black Dust around the Duct Openings

If you start noticing mold spots and mold dust, your problem already got much bigger. Usually, the infestation is quite advanced if you actually see the mold at the duct openings, ceilings, or walls. Mold looks differently, depending on the species infesting your house. It can look like a white, fluffy deposit or green-blue spots. Black mold, one of the most dangerous kinds, looks like black dust covering your duct grids, and you might mistake it for regular dust.

Allergy-like Symptoms

A mold infestation usually comes with health symptoms that are similar to respiratory allergies. You will get a runny nose, watery eyes, coughing, and sneezing, etc. If these symptoms disappear as soon as you leave the house or you stop using the air conditioner, it’s a sign that you might deal with mold.

Headaches, Breathing Problems

Some of the worst symptoms you can get from mold growing in your air conditioning system are headaches, dizziness, breathing problems, and other more serious signs. For people with certain conditions, such as asthma, these respiratory problems can be exacerbated and degenerate in an emergency.

If you notice one or more of these signs, seriously consider a mold infestation and investigate further. Calling an AC service is the best way to deal with such a problem because DIY solutions may not be safe or as effective as specialists. In addition, if you want to prevent such problems, then it would be wise to schedule maintenance visits at least once a year.

Thomas Hoffmann Air Conditioning & Heating

Thomas Hoffmann Air Conditioning & Heating specializes in installing, repairing, and maintaining the cooling system for your home. We are dedicated to keeping our customers cool in the hot summer months by selling the best air conditioners on the market, providing preventative maintenance services, and sending out our certified technicians to service your existing equipment.

24/7 Service Call Now

At Thomas Hoffmann Air Conditioning & Heating, we pride ourselves on being a locally owned and operated HVAC company. With more than 30 years of experience and a master technician and mechanical engineer as our owner, we can replace, repair, and maintain your business or home’s HVAC system.

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