UV Light
A UV lamp aimed at the right surface is a genuinely useful piece of equipment. Aimed at the wrong one, it is decoration. We install it where the biology actually lives — on the cooling coil and in the drain pan.
What a UV system is actually for
The cooling coil inside your air handler is wet for most of the summer. It is dark, it holds condensate, and it collects the fine organic dust that gets past a filter — which makes it the most reliable place in a house for mould and bacterial films to establish. That growth is what produces the sour, damp smell some systems develop, and as it thickens on the fins it also insulates the coil and quietly reduces capacity.
Ultraviolet germicidal irradiation addresses that directly. A correctly placed lamp keeps a continuous dose on the coil face and the drain pan, which suppresses microbial growth on the surface rather than trying to catch organisms in a fraction of a second as air rushes past. This is the application with the strongest track record, and it is the one we recommend first.
In-duct air-stream systems exist as well, and they can contribute, but their effectiveness depends entirely on dose: lamp output, reflectivity, and how long air is exposed as it passes. Anyone who tells you a single small lamp in a duct sterilises the air in your house is overselling it. We will size and place equipment for what it can genuinely do, and we will tell you where filtration, source control and humidity management matter more.
What the service includes
- System assessment first — coil and drain pan condition, cabinet geometry, air handler access and existing filtration reviewed before anything is specified.
- Coil irradiation lamp sized and positioned for continuous, even coverage of the coil face and the drain pan.
- Ozone-free lamp selection — we do not install ozone-generating equipment in occupied homes.
- Optional air-stream lamp where the duct geometry can deliver a meaningful dose, explained honestly rather than upsold.
- Sealed, safe installation: no direct line of sight from occupied space, viewport where the cabinet allows it, and no UV exposure to wiring, plastics or flex duct.
- Dedicated power and interlock so the lamp is off when the cabinet is open, protecting whoever services it next.
- Coil cleaned first if needed — UV suppresses new growth, it does not remove an existing biofilm.
- Labelling and a service date on the cabinet so lamp replacement does not get forgotten.
- Annual lamp replacement service, because output falls well before the lamp stops glowing.
Honest expectations
Here is what a well-installed coil UV system does: it keeps the coil and drain pan clear of the microbial growth that causes musty odours and reduced coil performance, and it keeps them that way continuously without chemicals. Households that get a damp smell every summer when the air conditioning starts are usually the ones who notice the biggest change.
Here is what it does not do: it does not filter. UV removes nothing from the air — no dust, no dander, no pollen, no smoke particulate. It does not fix a dirty duct, and it does not compensate for a filter that fits badly or is rated too low for your needs. It also cannot treat what never passes it, which is why we talk about filtration and humidity in the same conversation.
We also avoid making health claims. ASHRAE recognises UVGI as a legitimate engineering tool and it is used widely in commercial settings, but a residential lamp is not a medical device and we will not sell it as one. Our position is simple: install it for coil hygiene and odour control, size it correctly, keep the lamp current, and let the rest of your indoor air strategy do what it is better at.
Signs you need this service
- A musty or sour smell when the air conditioning first starts, then it fades
- Visible dark growth or slime on the cooling coil, in the drain pan or in the plenum
- Recurring condensate drain clogs from biological sludge
- Coil that needs cleaning far sooner than it should after each service
- A humid climate or a home that runs cooling for most of the year
- Household members sensitive to mould odours, or a history of moisture problems in the system
- An existing UV lamp that has been in place more than a year — output has almost certainly fallen
Assess, place, protect, schedule.
Placement and dose are the whole game with UV — so the install is engineered, labelled and put on a service calendar.
Assess
We inspect the coil, drain pan and cabinet, review your filtration and any odour history, and recommend coil irradiation, an air-stream lamp, both, or neither — with the reasoning in writing.
Clean the surface
If there is existing growth on the coil or in the pan, it is cleaned first. UV prevents re-establishment; it does not dissolve a biofilm that is already there.
Install
The lamp is mounted for even coverage of the coil face and pan, with dedicated power, interlock or labelling, no light path to occupied space, and nothing UV-sensitive in the beam.
Label and schedule
The cabinet is labelled with the lamp model and replacement date, you receive photographs of the installation, and the annual lamp service goes on the calendar so performance does not quietly disappear.
UV Light: common questions
Straight answers, no pressure. Call us if yours is not here.
No, and that is the most common misunderstanding. UV inactivates microorganisms it irradiates; it removes no particulate whatsoever. Filtration handles dust, dander and pollen. The two do different jobs, and a UV lamp installed to compensate for poor filtration will disappoint you.
If the smell comes from growth on the coil or in the drain pan — which is the usual source — cleaning the coil and then keeping it under continuous UV is the right treatment and usually resolves it. If the odour is coming from wet insulation, a rodent problem or standing water elsewhere, UV will not touch it, and we will find that first.
Installed correctly, yes: the lamp is inside a sealed metal cabinet with no line of sight into occupied space, and it is interlocked or clearly labelled for whoever opens the unit. We only install ozone-free lamps, and we keep UV off plastics, wiring and flex duct because it degrades them.
They typically continue to glow for years while germicidal output falls off substantially, often within twelve to eighteen months. That is why we label the install date and recommend annual replacement — a glowing lamp is not proof of a working system.