Synopsis: Using foam insulation is a common way to stop airflow through recessed can lights, which are notorious energy wasters. Unfortunately, the temperatures inside a foam enclosure can get hot enough to melt the foam or the wiring inside the enclosure, creating a fire risk. Veteran electrician and building-science expert Larry Armanda points out the potential dangers and shows how to seal up can lights safely and effectively. To determine just how hot it can get inside a can light enclosure, Larry constructed a purpose-built test rig and monitored the temperature inside with a four-channel data logger. Then using his temperature data, he designed a safer enclosure with modern wiring, a heat-resistant enclosure, and a long-lasting LED light bulb. Two detailed illustrations that complement the article show both a conventional can-light enclosure and Larry’s safer enclosure.

I’ve been an electrical contractor and a building-performance professional for more than 35 years. Over the past two decades, I’ve read countless articles in Fine Homebuilding and other magazines that describe the use of enclosures built from drywall and foam insulation to air-seal can lights in attics. Sealing these notoriously leaky fixtures — which waste energy, allow moisture into the attic, and contribute to ice dams — is a good idea. Unfortunately, the way many builders and weatherization professionals approach the work is potentially dangerous. The problem is that heat generated by the lightbulb and trapped within the enclosure can melt the wiring’s plastic insulation, leading to arcing and fire.

Air-sealing can lights safely isn’t a new concern of mine. I did my first research in 2001 and published the results in Home Energy, a magazine for the weatherization industry.

I recently completed new research into the subject. This time I built a more comprehensive test rig that mimicked common ceiling construction, and…