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Question DetailsAsked on 5/27/2011

How to deal with mold in furnace

I had my furnace and A/C cleaned and inspected today. I was told (and saw evidence of) there was mold in the coil. Besides getting things cleaned out, it was recommended that I purchase a UV light systems to go in the furnace to prevent this. Does anyone know whether this is the best way to deal with the problem? I looked on the internet but got conflicting information about how effective this is. Also, should I get my air ducts cleaned to get any mold cleaned up there? I have to say we have noticed an increase in allergy symptoms in the past year.

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5 Answers


Hi Maureen,

You are correct. There is much conflicting information out there regarding mold removal and air duct cleaning.

We wanted to help you with your problem, so we contacted several highly rated HVAC service professionals on Angie’s List to get some advice.

Most professionals agree: Mold in the coil pan is not uncommon, due to the high volume moisture present in the area. Using a high quality air filter can help keep pollutants and particles out of your system.

Humidity in your home may also play a factor in terms of mold, so an ultra-violet light would be considered one measure of alleviating the problem. UV lights work by using intense rays of ultraviolet light to dramatically reduce concentrations of potentially harmful microorganisms by stopping their growth.

An inspection of the duct cleaning system should help determine whether there is mold present. Many companies offer video inspections so you can see for yourself what is in your ducts. Beware of the companies that offer the $49-$99 cleanings. A quality air duct cleaning typically will cost several hundred dollars. A cleaning should include all components of your HVAC system, including the coils, drain pans, fans and humidifiers. If just one component of the system is not addressed, that could result in re-contamination of the entire system.

If there is mold present, you should have your air ducts cleaned by a company that is experienced in mold remediation. While there is no scientifically proven health benefit to having the air ducts cleaned, the duct system can serve as a collection center for spores, pollen, dander, dust and a host of other contaminants. Removing these particulates and contaminants by having your air ducts cleaned and adding a UV light may help to alleviate any health issues, such as allergies and asthma.

In lieu of the UV system, some companies spray the A coil with a micro biocide sanitizer that can help control harmful organisms.

You should get always get at least two to three opinions and estimates from certified and trained HVAC technicians before having any work done.

I hope this information is helpful.

Please let us know how it turns out!

Paul from Angie’s List

Answered 9 years ago by Paul from Angie's List


Hi Paul and everyone,

Your answers are very good...I also have a mold problem...perhaps you can get some answers for me.

Our problem involves a smell coming from our heat pump/air conditioner. First we thought it was a mold smell...we installed UV lights, had ducts fogged..and finally put in a whole house dehumidifier.[sized for the house sq ft]

Smell is very caustic...not all people smell it...gets to my throat and eyes tear.

The dehumidifier seems to help until it gets very humid outside. Humidify gauge shows 55% of air coming out of vents and the gauge set in individual rooms can show 60%, even though the humidifier is set to full. When rooms % shows 57% I start to get the smell.

There is no visible mold in the ducts. I have heard of dirty sock syndrome. Could this smell be dirty sock syndrome? I've read that this smell is not irritating.

Is the smell from dirty sock influenced by the humidity? We did not have ducts fogged for this.

Any idea what is going on here ...AND what can be done to get rid of the smell?

Answered 9 years ago by houndog


Hi Houndog,

We consulted more than a dozen highly rated HVAC and air quality specialists to get an answer to your question.

With unidentifiable odors, there could be a number of possibilities. The “dirty sock” smell you describe could be related to your home’s high humidity level. The acceptable level of relative humidity in your home should be between 35 and 55 percent. If possible, try to bring yours down into the mid-40s.

A clean HVAC system starts with clean filters, so make sure you are changing yours regularly and are using a good HEPA filter. Your AC unit is a breeding ground for mold, and it can commonly grow in the air return, distribution plenum and evaporator coils, so it’s important to have that checked. An annual routine maintenance plan can help catch mold problems.

You may consider having air quality samples performed to ensure your home’s air quality is within normal levels. It is imperative that a qualified person does the testing, takes both indoor and outdoor samples, and sends those to a certified lab for analysis. If mold is not the issue, you could have your home tested for volatile organic compounds, however it’s important to rule out other potential causes first, as VOC testing from a Certified Industrial Hygienist can be expensive.

Your air ducts could need a thorough cleaning, which means installing UV lights and fogging might not be enough. Avoid air duct cleaning companies that offer the $99 cleanings. A good cleaning will cost several hundred dollars.

If you think moisture is causing your problem, you can hire a certified thermographer to perform a moisture inspection.

That this odor irritates your throat and eyes is concerning. Some homes – especially in the south and southeastern parts of the United States – that were built after 2000, contain Chinese-made drywall that has caused a host of problems for homeowners, including producing a sulfur “rotten egg” odor, corroding coils and wiring throughout the home, and causing health problems including irritants similar to what you describe. A qualified home inspector or Certified Industrial Hygienist should be able to help you determine if your home has Chinese drywall and what steps to take if it does.

I hope this helps. Please let us know if you identify the problem. Best of luck.

Paul from Angie's List

Answered 9 years ago by Paul from Angie's List


I am new in the Torrance city and need a good home. I searched lot in internet about this website, Is this website is really good in providing good inspection?

Answered 9 years ago by fink1434


Hi Houndog,

We're working on an answer to your question, but the potential problem and solutions could hinge on when your home was built. How old is your home?


Paul from Angie's List

Answered 9 years ago by Paul from Angie's List

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