A Recessed Can of Worms

January 01, 2001
January/February 2001
This article originally appeared in the January/February 2001 issue of Home Energy Magazine.
Click here to read more articles about Roof & Attic

        As weatherization consultants and trainers, we see many kinds of problems in different homes. A few years ago, we received a call to solve an unusually high bill complaint. The homeowner who called us had been referred to us by the local electric company. The house, a large new luxury home in Harrisburg, Pennsylvania, was heated with electric-resistance baseboards and cooled with two central air systems. The utility bills for the winter months ranged from $680 to $1,220. The homeowner told us that the house was uncomfortable and had other problems—the most dramatic one being the ice dam that formed on the back of the house. It broke loose, and crushed the two A/C units on the ground below! A contributing factor to both the high bill comlaint and the ice dam was the recessed-can lighting.
        We proceeded to perform an air leakage test and an infrared scan of the home. We pressure-panned all of the registers and took notes on the size and physical characteristics of the house. We noted that the first and second floors were heavily lit using recessed-can lighting fixtures—134 in all. On the second floor, below the attic, we counted 56 recessed-can lights. A closer inspection of the fixtures revealed that they were all non- IC–rated fixtures (see “Recessed-Can Light Basics”, p. 43). This is important, because thermal insulation may not be installed in contact with a recessed-can light if it is rated “non-IC” (see “Wiring and Safety” p. 44). During the air leakage test, we noted air leaking from most of the recessed fixtures, including all 56 fixtures on the second floor.
        When we climbed up through the attic hatch, we were surprised by what we saw. The attic was partially floored with plywood and insulated with cellulose. Prior to insulating, the installer had carefully fitted 12-inch-tall sheet metal barriers around each light fixture. There were what looked like 56 short, opentopped, sheet-metal chimneys protruding into the attic through both the insulation and the plywood floor.
        This treatment is the most commonly prescribed method for protecting non-IC recessed lights from insulation contact. Attic preparation, in this case, had been done by the book! However, the energy implication of this sort of by the bant. It creates a huge sook treatment is significection of the ceiling that is not insulated. In addition, since most recessed-can light fixtures are full of holes that allow for adjustments that may be necessary for different bulbs, the fixture is a serious air leakage site. An air leakage problem may also contribute to or cause a moisture problem. There was no doubt that, in this particular house, one of the factors that contributed to the glacier on the roof was the existence of so many leaky recessed-can lights leaking heated air into the attic.

                Plugging the Leaks
        What treatment can a contractor use that is a safe and effective method of recessedcan light repair?
        Some contractors fabricate boxes made of sheetrock to enclose the fixture. This box method addresses the air loss issues as well as keeping the light a safe distance from the insulation, but is it a safe retrofit?
        The 98 International Energy Conservation Code (IECC) requirements for non-IC rated fixtures include a mandate that they be “installed inside a sealed box constructed of a minimum of 1/2-inch gypsum wallboard or constructed from a preformed polymetric vapor barrier, or other material manufactured for this purpose, while maintaining required clearance of not less than 1/2-inch from combustible material and not less than 3 inches from insulating material.”
        So in order to plug the leaks in this home’s ceiling in the way required by the building code, each recessed-can light would have to be enclosed within a sealed and airtight box. But how safe is this method? Several issues must be addressed to answer that question:
        How much heat is generated inside the airtight box?
        Does the heat get trapped within the fixture, creating a safety issue involving the wiring or the lamp holder?
        What is the temperature rise inside the air sealed box during the summer, when attic ambient temperatures can reach +130ºF?
        What is the temperature rating of building wire, old and new?
        Because the energy code specifies constructing this airtight box above the recessed-can lights, we decided to see what would happen in a variety of situations regarding safety issues. We knew the client’s energy problem in this house could be fixed, but we wanted to make sure it was a safe fix.

                In the Lab
        With the goal of measuring the temperatures that would result within an airtight box such as the one required under varying ambient air temperatures using bulbs of various wattages and styles, we took the problem with us into the laboratory. First, we installed a recessed-can light housing in a simulated ceiling section with a 1/2- inch Sheetrock surface on the bottom of the frame to simulate a drywall ceiling.
        Then we suspended the frame 36 inches above the floor. The light housing was equipped with an open black baffle trim. We removed the thermal overload switch and jumpered it to prevent the temperatures generated by the lamps from shutting off the light. Then we fitted the frame with an airtight box made of 1/2-inch drywall, and measuring 13 inches x 16 inches x 10 1/4 inches. This box was built in accordance with the IECC 98 requirement to maintain 3 inches of air space around the fixture.
        We installed 12-inch fiberglass batt insulation around, but not over the top of, the airtight box. Finally, we installed thermocouples in four different locations to allow us to monitor temperatures within, on and above the box. When the box was completed, we conducted three different tests to see how it would perform under different conditions and with different lamps. The results of these tests are shown in Table 1.
        Test 1. Here we tested the temperatures above and around a variety of bulbs when the ambient temperature above the box was approximately 70°F.
        Test 2. Here, all seven lamps were tested in a summer condition, representing a potentially dangerous situation if the lights were left on all day during a hot day. To simulate summer attic temperatures of 135°F, a polyisocyanurate foil-faced rigidboard insulated box (R-7.2) measuring 28 inches x 53 inches x 241/2 inches was built and placed over the entire 2 inch x 6 inch frame. We cut an inspection window into the top of the box directly above the light fixture and sealed it in place with silicon caulking. To obtain an average summer attic temperature of 135°F around the outside of the air sealed fixture box, we placed a 300W lamp inside the insulated outer box. This light was controlled by a Chromolox thermostat to maintain temperature.
        The 60W standard lamp indicated a temperature of 147°F, and the 100W standard lamp a temperature of 164°F inside the air sealed fixture box. In summer conditions with 135°F attic ambient temperature, both lamps exceeded the legal limits of the wiring inside, considering that this was a box for an older style fixture with a 140°F rating. Likewise, the 100W standard lamp exceeded the temperature limit with an ambient temperature of 72°F. The 120W Capsylite flood lamp indicated a temperature of 140°F, which is at the limit of the temperature rating of the wiring. Because these older fixtures were not protected with thermal overload switches, this result clearly suggests the possibility of wire insulation damage, and may suggest the possibility of a fire hazard.
         The 75W reflector flood and the 90W Capsylite flood lamp indicated temperatures of 122°F and 129°F respectively, well below the 140°F rating of the wiring.
        The 20W and 23W compact fluorescent lamps (CFLs) indicated the lowest temperatures— 110ºF and 114°F, respectively. (Both fluorescent lamps tested had a manufacturer average rated life expectancy of 10,000 hours. According to some of the manufacturers, this life expectancy can be cut in half if the lamp is installed in a recessed-can light. This reduction in life expectancy could be due to the reduced air flow around the ballast of the lamp, which is located in the base of CFLs.)
        Test 3. In this last test, a 60W A lamp with a gasketed glass shower trim was installed on the fixture. R-5 fiberglass batt insulation was loosor summer conditions of 130ºF–135ºF. This is absolutely thely laid over the top of the air sealed box. The test was set fe worst-case scenario, because the lens on the bottom of the light and insulation over the top of the enclosure really trap the heat.
        These temperatures went well over the rating of the fixture wiring. The temperature inside the electrical terminal box—183°F— even came close to the temperature limit of 194°F for the newer thermally protected fixtures. If a 100W standard lamp had been installed, I suspect the temperature would have gone sky-high, possibly creating a serious overheating problem. The fire hazard in this case, depending on the combustibility of material around the lamp and lamp housing, could be very great.

                Safety First
        As our test results showed, before you follow the IECC requirement of building an airtight box constructed of at least 1/2-inch gypsum wall board, you need to address the following considerations:
        Determine the age of the light fixture and the building wiring in order to determine if there is a thermal overload switch installed on the light fixture, the temperature rating of the fixture wire, and the temperature rating of the building wiring.
        If there is a lamp label inside the trim, make sure the proper type of lamp is installed. If there is no label, check the lamp socket for the maximum lamp wattage allowable. To help prevent a homeowner from overlapping the fixture (putting in a higher-watt bulb than the manufacturer recommends), mark the inside of the fixture adjacent to the lamp with the style and wattage of the replacement lamp. Alamps should never be used in any type of recessed-can fixture. CFLs or PAR lamps are a safer choice.

        If you build an airtight box around a recessed-can light, as code requires, we suggest that you take the following precautions for safety reasons and to allow an energy efficiency retrofit:
• Use only PAR (reflector-type) bulbs or CFLs.
• Do not use any bulb that exceeds 75 watts.
• Make sure the airtight drywall boxes maintain a minimum of 3 inches of clearance to all parts of the fixture, including the terminal or junction box.
• Do not place insulation over the top of the drywall enclosure.
        The builder of the house we inspected should have installed IC-rated, airtight recessed-can lights. Given the situation we found, we felt that the best alternative to replacing all of the lights was to build the airtight drywall enclosures. This was indeed an important energy-efficient fix. We did, in fact, make this recommendation to the homeowner.
        Only by understanding recessed-can light fixtures, building airtight boxes, and addressing the temperature and safety issues associated with them can contractors safely keep heat and moisture from entering the attic space, as well as keep glaciers from forming on our roofs.

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