How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

site-built, mobile/manufactured and modular homes

What does an ultraviolet air treatment system do?

Saturday, September 22, 2018

It bathes the area around it with UV-light, killing any bacteria and virus, along with some mold reduction, on the surfaces it shines on and also in the air it shines through. The technical term for it is “ultraviolet germicidal irradiation,” and it has only line-of-sight effectiveness. If the UV-light is not shining on a surface, then it will not be disinfected. 

   The photo above shows a unit manufactured by Honeywell installed in a supply air duct above an air conditioning air handler’s evaporator coils. When installed in this location, it treats both the surfaces of the evaporator coils and the air flowing through the duct. The photo below shows the same unit before installation.

    The system can also be installed in the return air duct to treat all incoming air in the air conditioning system. This particular UV-light system is activated by air flow in a duct.

    A UV air treatment system, in conjunction with an air filtration media, can be helpful for people with allergies or a compromised immune system and, when the evaporator coil area is irradiated, it can also reduce the musty smell emanating from a system with mold growth on wet surfaces by killing the mold. 

    Unfortunately, although a UV light can kill mold on the evaporator coil surfaces that it shines on directly and continuously, mold spores floating in the air through the evaporator coil are not exposed to the light long enough to have an effective kill rate. 

    UV air treatment devices come in many shapes and sizes, and the Honeywell unit is just one example. But, if you see a small  to medium-size box stuck on the side of a main supply or return duct near an air handler and it has the words “ultraviolet” on it along with a warning about not directly viewing the light, then it is likely a UV air treatment system.

• • • • • • • • • • • • • • • • • • • • • • • • • • • • 

  To learn more about heating and air conditioning systems, see these other blog posts:

How can I find out the SEER of my air conditioner? 

My air conditioner won't turn on. What's wrong? 

How can I find out the size of my air conditioner? 

How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump? 

Where is the air filter for my central air conditioner and furnace? I can’t find it? 

Does an old air conditioner use more electricity as it ages? 

How did homes stay cool in Florida before air conditioning? 

What is wrong with an air conditioner when the air flow out of the vents is low?

Why has the thermostat screen gone blank? 

Why does it take so long to cool a house when an air conditioner has been off for a while? 

Why is my air conditioner not cooling enough? 

What are the most common problems with wall/window air conditioners?  

Will closing doors reduce my heating and cooling costs? 

   Visit our HEATING AND AIR CONDITIONING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

Water Heaters

Water Heater Age

"What Are The

Signs Of..."

Septic Tank Systems

Structure and Rooms

Plumbing Pipes

Termites, Wood Rot

& Pests



When It First

Became Code

"Should I Buy A..."

Park Model Homes


Shingle Roofs




Wind Mitigation

Roof and Attic

"Does A Home


Pool and Spa

"What Is The Difference Between..."




Concrete and

Concrete Block

Metal Roofs


Modular Homes

Rain Gutters

Mold, Lead & Other Contaminants


Older and

Historic Houses

Crawl Spaces

Mobile-Manufactured Homes

Building Permits

Life Expectancy

Clay Soil





Exterior Walls

& Structures


Common Problems

HUD-Code for

Mobile Homes

Garages and Carports

Flat (Low Slope) Roofs

Electrical Panels

Sprinkler Systems

Electrical Receptacle Outlets

4-Point Inspections

Hurricane Resistance

Frequently Asked Questions (FAQ)

Home Inspection

Heating and Air Conditioning

Building Codes

Fireplaces and Chimneys

Inspector Licensing

& Standards

Energy Efficiency

Washers and Dryers



Doors and Windows



Electrical Wiring

Click Below  

for Links

to Collections

of Blog Posts

by Subject

Plumbing Drains

and Traps


Smoke & CO Alarms

Aging in Place

Top 5 results given instantly.

Click on magnifying glass

for all search results.






Air Conditioner & Furnace Age/Size


Electrical Switches





Water Intrusion

Electrical - Old

and Obsolete


Foundation Certifications

Tiny Houses

About McGarry and Madsen



Buying a home in North/Central Florida? Check our price for a  team inspection by two FL-licensed contractors and inspectors. Over 8,500 inspections completed in 20+ years. In a hurry? We will get it done for you.

Moisture Problems

Crawl Spaces