UV air purification in an HVAC system means one or more ultraviolet-C (UV-C) lamps mounted inside the air handler or the ductwork. In a Daly City home it can be useful, but it is often sold for jobs it does not do. Here is a straight account of both, and of the one question that decides whether it is worth the money on the fog side of the hills.
Two kinds of lamps, two different jobs
Coil lamps sit just above or beside the evaporator coil, the cooling coil of an air conditioner or heat pump, and shine on it all the time. The coil and its drain pan are wet whenever the system cools, and that wet surface is where a slimy film of mold and bacteria can grow, slow the airflow and cause a musty smell when the cooling starts. Constant UV-C exposure limits that growth. This is the job UV-C does most reliably, because the coil gets a steady dose, hour after hour.
In-duct (air-stream) lamps treat air as it passes. Air moves through a duct in a fraction of a second, so each pass gets only a brief dose. How much any given organism is affected depends on lamp power, the length of exposure and how many times the air circulates. We show you the lamp’s rated output rather than promise a result.
What UV does not do
- It does not remove dust, pollen, pet dander or smoke particles. Those need a filter; see air filter replacement or whole-home filtration.
- It does not remove odors or chemical fumes. Activated carbon and ventilation handle those.
- It does not clean a coil that is already coated. A dirty coil should be cleaned first; the lamp then helps keep it that way.
- It does not fix a damp house. If the musty smell comes from cool, damp rooms rather than the system, look at musty smells and moisture control instead.
- It is not a health treatment. Some lamps are marketed with claims about illness or sick building syndrome. We describe what a lamp does to surfaces and air, not what it does for anyone’s health.
The deciding question: does your system have a wet coil?
- Furnace only, no AC or heat pump. There is no cooling coil for the lamp to protect. If that is your setup, skip the UV light and spend the money on filtration.
- AC or heat pump that cools only on a handful of days. The coil is wet only when the system cools. A heat pump heating in winter runs its indoor coil warm, not wet. A lamp does less here than on a system cooling all summer.
- A history of a slimy coil, a musty smell when cooling starts, or a slow-draining pan. This is where a coil lamp earns its place, together with cleaning and a clear drain.
- Offices and labs that cool year-round. Buildings with a lot of equipment and people inside, such as the office and lab space east of Highway 101 in South San Francisco, keep their coils wet for far longer. There UV is one tool alongside ventilation, filtration and regular commercial maintenance.
Installation and safety
Most installs take 1 to 2 hours. The lamp is mounted where it reaches the coil face, or in the duct for an air-stream unit, and powered from the air handler through a switch that cuts it when the panel is opened. A viewing port or indicator lets you check it is on without looking at the lamp. Two details separate a careful install from a quick one:
- Plastics and flex duct. UV-C breaks down many plastics, wire insulation, filter frames and the inner lining of flex duct over time. The lamp goes where it lights the coil, not nearby plastic parts, and shields go where needed.
- Ozone. Some UV lamps also emit a shorter wavelength that makes ozone. In an occupied home, choose lamps sold as ozone-free.
Never look at a lit UV-C lamp; it can injure eyes and skin. Lamps typically need replacing once a year, since their UV output fades long before they stop glowing.
What it costs
UV light installation runs $400 to $1,000 per system. A single coil lamp in an accessible air handler sits at the low end; dual lamps, in-duct air-stream units and harder access cost more. Replacement lamps are an ongoing yearly cost. You get a written estimate before any work begins, and if your system has no coil that would benefit, we will tell you before you spend anything.