# UV light as germicide in A/C unit **URL:** \ **Category:** Factual Questions\ **Created:** [July 16, 2012, 1:34pm UTC](https://boards.straightdope.com/t/uv-light-as-germicide-in-a-c-unit/628409 "2012-07-16T13:34:06Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![carlb](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carlb/32/5930_2.png) [@carlb](https://boards.straightdope.com/u/carlb)\ **Post date:** [July 16, 2012, 1:34pm UTC](https://boards.straightdope.com/t/uv-light-as-germicide-in-a-c-unit/628409/1 "2012-07-16T13:34:06Z")
Looks like it’s time to replace the a/c system in our house. I’m in the quote-gathering process, and I’ve been getting the option to install a UV light in the air handler as a germicide. Anything definitive on the effectiveness of these things? My Googling has turned up a lot of literature from HVAC companies, but precious little from anything that looks like an impartial source. FWIW the house is in Florida, which seems to grow creatures of various sizes at an alarming rate, so anything that legitimately cuts down on the number of organisms residing in my house at any one time is worth considering, IMHO. I just want to make sure I’m not buying into any woo. ---
**Author:** ![lazybratsche](https://avatars.discourse-cdn.com/v4/letter/l/ba8739/32.png) [@lazybratsche](https://boards.straightdope.com/u/lazybratsche)\ **Post date:** [July 16, 2012, 1:57pm UTC](https://boards.straightdope.com/t/uv-light-as-germicide-in-a-c-unit/628409/2 "2012-07-16T13:57:49Z")
It’s definitely not woo, UV is used to disinfect lots of things. Some sewage treatment plants will use UV as a back-up method of disinfection, to kill the occasional bug that survived earlier treatment steps. In biology labs, UV lights are used to disinfect sterile cabinets, though again it’s a back up meant to catch anything that’s survived other cleaning methods. I’ve used UV light to kill a thick layer of E. coli on a petri dish. 10 minutes exposure under really really bright UV lamps will kill most (but not quite all) bacteria. Now, in an AC system I can’t say how effective it’ll be. At the very least, it should slow the growth of whatever is inhabiting the system. So if you have some aggressive molds that like to grow on, say, the evaporator coils or filters, that UV light should mean that you don’t have to clean or replace things quite as often. I can’t say if it’ll make a practical difference though. ---
**Author:** ![Red\_Stilettos](https://avatars.discourse-cdn.com/v4/letter/r/fbc32d/32.png) [@Red\_Stilettos](https://boards.straightdope.com/u/Red_Stilettos)\ **Post date:** [July 16, 2012, 2:02pm UTC](https://boards.straightdope.com/t/uv-light-as-germicide-in-a-c-unit/628409/3 "2012-07-16T14:02:14Z")
One thing to keep in mind is that the UV bulb will need to be changed fairly frequently to maintain efficacy, especially since it will be on constantly. I used to manage a aquatic system that used UV sterilizers to cut down on bacteria and algae. We changed the bulbs every 6 months, and I could tell when it was late, as the water started turning green. And the bulbs aren’t cheap. ---
**Author:** ![carlb](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carlb/32/5930_2.png) [@carlb](https://boards.straightdope.com/u/carlb)\ **Post date:** [July 16, 2012, 2:13pm UTC](https://boards.straightdope.com/t/uv-light-as-germicide-in-a-c-unit/628409/4 "2012-07-16T14:13:06Z")
Thanks, all. I knew UV had germicidal effects, but didn’t have any direct experience, or any knowledge as it relates to a/c systems. I think I might go with it; like I said, anything to keep all the wee beasties at bay. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [July 16, 2012, 4:21pm UTC](https://boards.straightdope.com/t/uv-light-as-germicide-in-a-c-unit/628409/5 "2012-07-16T16:21:09Z")
Before you commit to anything, I’d find out exactly how powerful the bulb is, and exactly how far away it is from the surfaces it purports to be disinfecting. You need quite a strong UV intensity to really do anything. We had UV disinfection bulbs in some of our lab hoods, and when we once measured the intensity of UV light actually reaching the hood work surface, it turned out it was no more effective than waving a blue light in the general direction. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [July 16, 2012, 4:40pm UTC](https://boards.straightdope.com/t/uv-light-as-germicide-in-a-c-unit/628409/6 "2012-07-16T16:40:22Z")
I’d vote for “Big waste of money.” ---
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [July 16, 2012, 4:52pm UTC](https://boards.straightdope.com/t/uv-light-as-germicide-in-a-c-unit/628409/7 "2012-07-16T16:52:09Z")
UV light applied to the coil will keep colonies from growing on the coil. UV light shone into the airstream will do absolutely nothing. We were offered systems which included both types of UV light installation when we had our handler replaced last year (and wound up plumping for neither, for what it’s worth). ---
**Author:** ![NBYodo](https://avatars.discourse-cdn.com/v4/letter/n/a9a28c/32.png) [@NBYodo](https://boards.straightdope.com/u/NBYodo)\ **Post date:** [July 16, 2012, 9:35pm UTC](https://boards.straightdope.com/t/uv-light-as-germicide-in-a-c-unit/628409/8 "2012-07-16T21:35:21Z")
We had a rep from Steril-aire ([http://www.steril-aire.com](http://www.steril-aire.com)) in at work for commercial HVAC, but they appear to also do residential systems. We weren’t specifically looking for air quality improvement systems, but they also claim energy usage improvements simply from increased airflow due to reduction in pressure drop across the coil from the biofilm. They indicate replacing the bulbs every year is the only typical maintenance required. Case studies on their website. YMMV. INASterilAireFlogger. NB