I decided to do this as I installed many of my light fixtures. I went around and (all cathedral with standard fan boxes) removed any lights already installed and switch covers, and blew in about 1.5-2 second worth of foam into all conduit pipes that went into the ceiling. So this included light switch boxes in the wall, all fire alarm boxes up in the upper wall/ceilings, outlet boxes that had a pipe going outside to another outlet, and all upstairs cathedral fan boxes. I shoved the bendable tube in the pipe as deeply as the can could reach (did not turn power off so I didn't want to make contact with any hot lines with the metal can). Call me crazy but I can feel the difference. We had a couple cold days in Chicago with some strong winds and one can definitely feel the difference. Of course, putting your hand next to the box results in no cold air feel. One of my rooms is above my garage surrounded by 5 sides with outside air and one side against the rest of the house. This room is the one that you feel the difference. Prior you can, in a subtle way, notice the high winds outside affecting the air quality in that room. After spraying the switchboxes, the three ceiling boxes and the outlet boxes (did all of em in this room), you notice it.
It wasn't hard, took a couple hours to use up one single can of greatstuff and that can covered all the upstairs ceiling stuff, the room over the garage, and some of the downstairs shared conduits with the exterior. Two cans will likely do all or the majority of a 3k SF home no problem. So for the cost and time involved it is not a big deal. A nice quick rewarding winter project.
For new construction, I think it's best to spray then attach your fixture so you can set the wiring while the foam is still tacky and solidifying. But if you spray it for a couple seconds there should be enough in there to prevent any separation and leakage if one were to do the hookups later. |