As a homeowner in St. Louis, you rely on your HVAC system to stay comfortable year-round.
But what happens when your heating or cooling system starts emitting unusual odors? At Thomas Hoffmann Air Conditioning & Heating, we understand that strange smells from your HVAC can be concerning.
In this article, we’ll explore common HVAC odors, what they might mean, and when it’s time to call in the professionals.
Very good, pleased with service.
Excellent service from Nick!
I am very pleased with the service provided.
, especially the quick response to my request . The technician came in themorning and had my cooling system repaired within an hour. Thank you !
Response from the owner:We're delighted we could promptly assist you on a Sunday morning and fix your cooling system efficiently. Thank you!
Here on time, worked fast. Always pleasant and great answering questions. Zach always does a great job.
Response from the owner:Thank you, Debra, for your kind words; we're glad to hear Zach made a positive impression and that you had a great experience with our team!
great job
Response from the owner:Thank you, Joe! We appreciate your kind words and the support from everyone involved.
Extremely quick response for appointment and did quick fix for our furnace and heat is working great !
Response from the owner:Thank you for your kind words! We're glad to hear our team was able to respond quickly and get your furnace working great. We appreciate your feedback!
They were timely, polite, professional and they saved us from too much sweating. In a field full of pompous and arrogant technicians, these guys take the time to explain what is wrong and how they are correcting it. Other folks just assume you are incompetent but these folks take the time to educate. Cannot recommend highly enough.
Response from the owner:Thank you for your kind words! We truly appreciate your feedback and are glad we could provide you with a positive experience.
Great service and arrived on time when promised.
Response from the owner:Thank you Wray, for your kind words! We're glad to hear you had a great experience and that everything was on time.
I would like to have a receipt for my payment which I did not receive. On a positive note he was very punctual very early actually he did his job and was very professional and I'm hoping and praying this took care of the issue thank you and I would not hesitate at this time to use your services
Response from the owner:Thank you, Mark, for your feedback and for highlighting the punctuality and professionalism of our team; we appreciate your support and will ensure you receive your receipt promptly.
Our experience with them was fantastic all the way through! Not only were they able to get to our business that day but the customer service from the phone call to the on-site service was professional and quick. We'll definitely be using Thomas Hoffmann Air Conditioning and Heating in the future.
Response from the owner:Thank you, Michelle, for your wonderful feedback! We're glad to hear about your fantastic experience and appreciate your kind words about our team's professionalism. We look forward to serving you again in the future!
Zachary was here on the dot at 8:00am. Thank for making me the first stop as promised. Very friendly too.
Response from the owner:Thank you for recognizing our professionalism and friendliness!
Competence and knowledge have been my experience.
Response from the owner:Thank you, Beth, for sharing your experience; it means a lot to us!
I couldn’t be happier with the service from Thomas Hoffmann Air-Conditioning! From the moment I called, the team was professional, responsive, and truly knowledgeable. Thomas personally made sure everything was handled with great attention to detail. The installation was smooth, efficient, and the quality of the work exceeded my expectations. It’s rare to find a company that is both skilled and genuinely cares about their customers. I highly recommend Thomas Hoffmann Air-Conditioning to anyone looking for honest, reliable, and top-notch service. They’ve definitely earned a loyal customer!
Response from the owner:Thank you, Rick, for your kind words and for recognizing our team's hard work; we're grateful for your support and thrilled to have earned your loyalty!
Amazing service from Thomas Hoffmann! They made space in their schedule to come out the next day to fix our air conditioner. They were on time, honest and fixed the problem on the spot. Thank you!
Response from the owner:Thank you, Ashley! We appreciate your kind words about our team's service – it's great to hear we could help you so quickly.
Excellent Service!
Response from the owner:Thank you, Lynda, for your kind words about our service; we truly appreciate your support!
Fast efficient service. Both of the gentlemen that came to my home were very help and informative not to mention polite. It’s difficult to get service advisers to appear at your home when scheduled most times they’re late or don’t show up at all. Not an issue with this team on time, clear diagnosis, quick repair. I would definitely use Thomas Hoffmann Air Conditioning again. I recommend them highly.
Response from the owner:Thank you, Anna, for your wonderful feedback! We're glad to hear that our team provided you with timely and helpful service, and we appreciate your high recommendation.
Tom was great. Super quick and easy! Serviced my unit in under 24 hours.
Response from the owner:Thank you, Olivia! We appreciate your kind words about Tom and are glad to hear your unit was serviced so quickly.
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.
The OG brother, Thomas Hoffmann, his son Nick, who and the entire team are fantastic! They have my highest respect and recommendation!
Response from the owner:Thank you, Jane! We truly appreciate your kind words about Thomas, Nick, and the entire team; your support means a lot to us!
Fast response and great quality work.
Response from the owner:Thank you for your kind words about our fast response and quality work; we truly appreciate your support!
Very quick and efficient
Response from the owner:Thank you, for your kind words; we appreciate your recognition of our quick and efficient service!
He got my ac up in running in no time.
Response from the owner:Thank you, T! We're glad to hear that everything is running smoothly and appreciate your recognition of our team's effort.
Giovanni was amazing. Explained everything in detail.and really made sure my unit is operating at its best. Very happy with them.
Response from the owner:Thank you, William! We're glad to hear Giovanni provided such detailed service and ensured your unit is running smoothly.
Came out immediately after a time slot opened and fixed the AC issue.
Response from the owner:Thank you, James, for your kind words! We're glad we could address your AC issue promptly.
Outstanding in every respect.
Response from the owner:Thank you, Ordont, for your wonderful feedback; we're so glad to hear everything met your expectations!
Zachary was very knowledgeable and informative! Highly recommend!
Response from the owner:Thank you, Beth! We're so glad you found Zachary knowledgeable and informative—we appreciate your recommendation!
First visit for my maintenance program. Arrived on time. Very polite to talk to. They discussed what they did and everything was good. They were professional. I would recommend this company to everyone.
Response from the owner:We're delighted to hear about your positive first visit experience with us! Thank you for recommending our services.
They were quick and did an exce
llent job on a very hot day. Thank you
Response from the owner:Thank you for the 5-star rating, Tom!
Very knowledgeable. Very professional. Tom was very thorough and finally confirmed the issues in the system that no one else bothered to check.
Response from the owner:Thank you, David, for your kind words; it's great to hear that Tom's thoroughness made a difference in addressing the issues in the system. We look forward to working with you in the future!
Excellent Service. Thank you Zackery
Response from the owner:Thank you for your kind words, Buzz! It was a pleasure assisting you.
I’ve been using “THOMAS Hoffmann Airconditioning and Heating” for years now. We have a 30 +\- year old system that works perfectly for us. Although we’ve not had to use it yet, it is comforting to know they offer a 24 hour on call service. I really appreciate that the technicians don’t try to upsell us on anything. They’re a very professional, knowledgeable, and courteous, local-family owned and operated business. I’ve also found their pricing to be very fair and by”fair” I don’t mean “cheap” but reasonable… especially for the quality of service provided by THOMAS Hoffmann HVAC. I love supporting smaller family owned business and this one is top-notch! Thank you guys!
Response from the owner:Thank you so much for your continued support and kind words, Mari! We truly appreciate your loyalty and are glad to hear about your positive experiences with our services. We look forward to continuing to provide you with top-notch service in the future.
Great customer service & experience for our HVAC System! They installed two UV lights and a dehumidifier. On time, great service, the new items work great - Great HVAC Service in St. Louis! Thank you!
Response from the owner:Thank you, Brandon, for your wonderful feedback! We're glad to hear that you had a great experience with your installations Your satisfaction is our priority!
Thank you Thomas Hoffman Air Conditioning for doing a great of repairing our HVAC system that was damaged during a power outage. You installed our new HVAC system late last year and promptly responded to our call for repair after a power surge impacted our subdivision.
Response from the owner:Thank you, Don, for your kind words! We're glad to hear that Thomas Hoffman Air Conditioning was able to assist you so quickly after the power surge and that you're satisfied with your new HVAC system. Your support means a lot to us!
Always great service!
Response from the owner:Thank you, Chris! We appreciate your kind words about our service and are glad to hear you had a great experience.
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.
Quick response and did a great job. On a Saturday.
Response from the owner:Thank you, Scott! We're glad to hear you appreciated the quick response and great service, especially on a Saturday. We look forward to continue serving you.
Super easy to schedule, arrived on time and quickly fixed my AC. Thank you!
Response from the owner:Thank you, William! We're glad to hear scheduling was easy and that your AC was fixed promptly. We appreciate your feedback!
Giovanni was good…. This is reason we ask for him
Response from the owner:Thanks so much!
As owner of rental and living out of town, it is very easy and painless to have Thomas Hoffman schedule all of my seasonal work with the tenant. Highly recommend!
Response from the owner:Thank you for trusting us with your rental property maintenance, Dan! We appreciate your recommendation!
Just had our annual service on our A/C. The technician, Giovanni, was very professional, friendly, thorough and spent time explaining what all he did and what his findings were. Couldn't be happier. I HIGHLY RECOMMEND THOMAS HOFFMAN AIR CONDITIONING AND HEATING.
Response from the owner:Terry, we're so grateful for your kind words and for recommending us! We're thrilled to hear that you had a positive experience with our technician during your annual furnace service. Thank you for choosing Thomas Hoffman Air Conditioning and Heating!
I called on December 25th at midnight and started leaving a message and Thomas Hoffman the owner called me back almost immediately. He said he would come out the next morning between 8:00 and 10:00 am snd he was promptly on time. He fixed my problem and while he was there I decided to get an estimate for a new furnace and air conditioning unit. The price was very reasonable and the installers one of them being his son were both very professional very courteous, polite, arrived on time and finished the same day. I enjoy knowing that I now have the support of Thomas Hoffman heating and air conditioning along with the peace of mind that comes with owning a Trane. Nothing stops a Trane.
Albert Koesterer
Response from the owner:Albert thanks so much for your kind reviews and your business. We truly appreciate it!!!
I made another service call years after my last review. Once again, Tom did not disappoint. He identified the cause of my newly purchased system installed by another HVAC company. He explained it so simple and easy to understand without the technical jargons. I just wished I had purchased the new equipment from Tom instead of saving a few hundred dollars from his competition.
Response from the owner:Thank you, J, for your kind words! We're glad to hear that Tom was able to assist you so effectively and make everything easy to understand. We appreciate your continued trust in our services and hope to help you again in the future!
I've used these guys twice now and their response time is great, they are friendly, informative, and most importantly, effective. I'm calling these folks every time my furnace sounds weird.
Response from the owner:Thank you for the wonderful feedback, Greg! We're glad to hear that you've had such positive experiences with our team. Providing timely and effective service is our priority, and we're here whenever you need us. Looking forward to assisting you again!
Nick fixed my furnace today, excellent service, very personable and quick service on the coldest day of the year. Thank you!!
Response from the owner:Thank you, Randy, for the fantastic 5-star rating; we appreciate your support!

Musty or Moldy Smell
If you notice a musty or moldy odor when your air conditioner runs, it could indicate the presence of mold or mildew in your system. St. Louis’s humid summers create an ideal environment for mold growth, especially in air conditioning units. This smell often results from:
- Clogged condensate drain lines
- Excess moisture in the evaporator coil
- Dirty air filters
Not only is this smell unpleasant, but it can also pose health risks, especially for those with allergies or respiratory issues. Regular maintenance, including changing air filters and cleaning drain lines, can help prevent mold growth.
Burning or Electrical Smell
A burning odor from your HVAC system should never be ignored. This smell could indicate:
- Overheating motor
- Frayed wires
- Burning plastic components
If you detect a burning smell, turn off your system immediately and call a professional HVAC technician. Continuing to run the system could lead to further damage or even pose a fire hazard.
Rotten Egg Smell
A rotten egg smell is often associated with a natural gas leak. While natural gas is odorless, utility companies add a sulfur-like scent to help detect leaks. If you smell this:
- Turn off your HVAC system
- Open windows for ventilation
- Leave your home immediately
- Contact your gas company or emergency services
Never ignore a potential gas leak, as it can be extremely dangerous.
Dirty Sock Syndrome
Yes, it’s an actual term in the HVAC industry! If your air conditioner emits an odor similar to dirty socks, it’s likely due to bacteria growing on the evaporator coil. This smell is particularly common in St. Louis during spring and fall when the AC runs less frequently. A professional cleaning of your evaporator coil can usually resolve this issue.
Chemical or Sweet Smell
A sweet, chemical odor could indicate a refrigerant leak in your air conditioning system. Refrigerant is crucial for your AC’s cooling process, and a leak can lead to:
- Reduced cooling efficiency
- Higher energy bills
- Potential health hazards
If you suspect a refrigerant leak, immediately turn off your AC and contact a certified HVAC technician.
Dusty or Burning Smell When Heat Turns On
It’s common to notice a dusty or slightly burning smell when you first turn on your furnace after months of disuse. This is typically due to dust accumulation on heating elements and should dissipate quickly. However, if the smell persists or becomes stronger, it could indicate:
- A clogged air filter
- Debris in the ducts
- An overheating component
A professional should check your system if the smell doesn’t go away after a day or two.
Gunpowder Smell
An odor similar to gunpowder often indicates an electrical problem, such as a failing fan motor or circuit board. This smell requires immediate attention from a qualified HVAC technician to prevent further damage or potential safety hazards.
Prevention and Maintenance
Regular HVAC maintenance is key to preventing many of these odor issues. At Thomas Hoffmann Air Conditioning & Heating, we recommend:
- Changing air filters regularly
- Scheduling annual professional maintenance
- Keeping your outdoor unit clean and free of debris
- Addressing any unusual smells promptly
By staying proactive with your HVAC care, you can ensure a comfortable, odor-free home environment throughout St. Louis’s seasons.
When to Call the Professionals
While some minor odors may resolve independently, it’s always better to err on the side of caution. If you’re experiencing persistent or concerning smells from your HVAC system, don’t hesitate to contact the experts at Thomas Hoffmann Air Conditioning & Heating. Our experienced technicians can diagnose and resolve your HVAC odor issues quickly and efficiently, ensuring your home stays comfortable and safe all year.
Call Now
Remember, a well-maintained HVAC system smells better and operates more efficiently, saving you money on energy bills and preventing costly repairs. Trust your nose – if something doesn’t smell right, it’s time to give us a call!