HVAC UV Lights

How To Kill & Prevent Mold

Mold is a silent menace in homes.

I would estimate that about 1-2 homes that I inspect have mold in their HVAC system — mainly the furnace. But I also frequently discover mold in bathrooms, basements, and other damp locations.

Mold cannot grow without the presence of water — either liquid water or high humidity (vapor).

In this guide, I will go over…

  • the best rated HVAC UV lights to kill and prevent mold
  • does UV light actually kill mold?
  • signs of black mold in air vents
  • pictures of mold in air ducts
  • getting rid of mold in your basement

Let’s get started with this guide!

What's In This Guide?

Ultraviolet light (specifically the UVC light frequency) has been in use for years in hospitals to sterilize operating rooms, equipment, and even food and water sterilization.

HVAC UV light bulbs are installed inside the furnace or A/C and shines 24 hours a day disrupting the nuclei of mold cells.

The interior air handler is a central place for mold to grow because it has three things that mold loves: high moisture, darkness, and a food source (dust).

Even though HVAC lights aren’t meant to clean mold from surfaces, they are a highly effective way to prevent mold from regrowing in the HVAC system (and spreading spores throughout the house).

Always clean your HVAC first if there is visible mold, then installing an HVAC UV light is highly recommended.

Here is my detailed review on the best rated 5 HVAC UV lights to kill and prevent mold.

During my home inspections, I have seen many signs of mold that indicated larger problems with the home.

I would say that 75% of the time, when I see mold growing on air vents, I discover mold inside the furnace or air conditioner.

Mold (sometimes mildew) growing on air vents has a dark and organic appearance.

When I am inspecting a home, it’s important to distinguish mold from just dust or debris.

Sometimes regular dust can accumulate, take on a dark appearance, and may be confused for mold. Either way, cleaning air vents (or replacing them) is a priority to maintain your indoor air quality. I also always recommend inspecting the interior of your A/C if you see signs of black mold in your air vents.

I invite you to read my full article on signs of black mold in air vents right here.

Over my years as a home inspector, I have compiled many pictures of what mold looks like inside the air conditioner.

Whenever I have indications that there may be a mold problem in a house, I always take off the HVAC furnace or A/C cover.

It is usually a simple process of turning a few latches, but sometimes it can be quite the ordeal.

Once the HVAC cover is off, I use a high powered flashlight to carefully inspect the blower fan, the evaporator coil, wiring, and the blower motor.

I find that the blower fan frequently has mold growth that many people miss. One reason for this is that dust can accumulate on top of mold growth on the blower fan fins — so an HVAC contractor may think it’s just dust.

Sometimes it is brain-dead obvious that there is mold growth — a black organic substance growing on electrical wiring, insulation, and on the coils.

If you would like to see some high quality photographs of what mold looks like inside an HVAC system (not just vent covers), you can check out my article here.

mold inside of furnace

One of the biggest fears that my clients have when buying a home is a moldy and leaky basement.

I usually try to placate this fear by using my moisture meter to carefully check all of the basements exterior walls for signs of high moisture.

Sometimes, I even give my client the actual moisture meter so they can check the basement themselves (this tool is very easy to use).

If you have signs of mold in your basement, there are certain steps you want to take to clean and remove the mold. Of course, any extensive mold contamination (more than 10 square feet) should be handles by a qualified contractor with experience in mold remediation.

But in this guide, for small areas of mold growth, I will go over some of my tips to clean and remove mold. And also importantly — I will detail the most common causes of basement water intrusion that actually fuels the mold growth.

Some of the steps are very simple, but quite significant; such as installing downspout extensions and improving the exterior landscaping.

To read my full article on how to get rid of mold in a basement, you can read it here.

Ultraviolet light has been in use for decades by hospitals and labs to sterilize biology and medical equipment from harmful microbial growth.

The actual light frequency is known as UVC and the wavelength is 253.7 nanometers.

Over the years, UV light has also been used to sterilize water and to kill harmful microbes at waste water treatment facilities.

One common recommendation to my clients is to install an HVAC UV light inside their air conditioner when I see signs of mold. I always tell them to have the furnace (and air ducts) cleaned by a qualified contractor first, and then install a UV light.

If there is visible mold, it’s important to clean it first, because even though ultraviolet light will kill the mold, the dead mold will leave behind a dusty residue that  can be an allergic irritant and cause health problems.

If you would like to read my full article on how UV light actually kills mold, you can check it out right here.

Mold is potentially a serious health and property problem.

Even though everybody responds differently to mold (some people are hardly affected), some individuals can develop serious health effects. And beyond health problems, mold if left unchecked, can literally eat away at structural wood framing and other building materials.

I once inspected a home (mainly for insurance purposes) where the entire basement was covered in mold. The owner went on vacation abroad for two months during the heat of summer, and he turned off the air conditioner.

Air conditioning actually has a dehumidifying effect so you should never fully turn it off during the warm season. And on top of that, the water heater sprung a small leak releasing a lot of moisture into the air.

Mold was growing on the walls, in the flooring, everywhere. In this case, the whole basement had to be demolished. Usually, mold doesn’t get that bad.

My most common recommendation is to clean up the mold, reduce all the sources of excess moisture, and then to install an HVAC UV light to help prevent it from regrowing.