Time

A few hours

Complexity

Intermediate

Cost

$20-50

Introduction

The small air gaps around electrical boxes on exterior walls and ceilings leak more air than you might imagine. A mere 1/8-in. gap around just six ceiling boxes is the equivalent of cutting a four-inch hole in your ceiling. Think of the amount of heat you'd lose if you did that!

When you consider all the leaks around all the electrical boxes in outside walls in your house, it's no wonder your house feels drafty, but you can fix this with some outlet insulation. Ceiling light fixtures add to the problem, because they let air pass into the attic. You can insulate those too. You'll save on your heating costs as well as staying more comfortable on those frigid winter days. We're here to show you how.

Tools Required

  • Caulk gun

Materials Required

  • Aerosol foam
  • Caulk

Project step-by-step (7)

Step 1

Stop the Drafts With Foam Outlet Insulation

Many homeowners install plain foam gaskets between electrical cover plates and the switches/receptacles. However, those gaskets don’t always seal well. Infrared thermograph images of those outlets will show cold air still entering the house (which means warm air escaping).

We’ll show you more effective methods that permanently seal those leaks. Sealing is easy to do and you can complete the entire house in about four hours. The materials cost less than $25, one of the best investments you’ll ever make! All you need is a caulk gun, caulk and aerosol foam.

While we’re at it, here are 10 ways to insulate your home without opening up walls.

Buy the Materials

Gaps around ceiling boxes must be sealed with an intumescent fire-blocking caulk or foam. Ordinary spray foam burns too quickly, opening the gap and creating a chimney effect that feeds the fire. Intumescent caulk or foam, on the other hand, swells when heated so it prevents that airflow. You can use regular caulk or foam on wall-mounted boxes.

If the electrical boxes aren’t mounted flush with the drywall, a box extender will make them easier to seal. You can find one for a rectangular, round or multiple-gang box at most home centers.

Fill Ceiling Box Gaps With Fire-Blocking Foam

  1. Turn off the power, check the wires with a voltage tester, then disconnect and remove the light fixture.
  2. Invert the spray foam can and shove the tube up into the gap between the electrical box and the drywall.
  3. Gently squeeze the trigger and slowly pump foam into the gap.
  4. Let it cure for about two hours.
  5. Cut off the excess and reinstall the light fixture.
    • Pro tip: Intumescent foam works best to seal large gaps (larger than 1/8 in.) around ceiling boxes. Be careful —  the foam drips out as it expands and is difficult to remove after it cures.

Plus, here’s how to install cove lighting.


Step 2

Flush-Mounted Wall Boxes: Seal the Wire Intrusions

  1. Align the tube on the spray foam can with the wire intrusion(s) and squeeze the trigger to shoot a small dollop of foam around the box opening.
  2. Enlarge the gap above and below the box (if needed) to provide room to insert the foam straw deep into the wall cavity.
  3. Then seal the wire intrusion openings with foam.
  • Pro tip: Don’t overdo it or the foam will force its way into the electrical box and you’ll have to remove the excess later. We used intumescent fire-blocking foam to seal the wire intrusions as an added measure of safety, but it’s not required by code. You can usually use regular spray foam for outlet insulation.


Step 3

Seal Around Flush-Mounted Boxes, Behind Electrical Cover Plates

Another simple procedure for better outlet insulation is to apply foam or caulk into the gap around the flush-mounted box, behind electrical cover plates. After the foam hardens, you can slice off the excess with a serrated knife. You can also seal the holes through which wires come into the box (intrusions). Here’s how:

  1. Seal the cable intrusions and the gap around the box first. To find the intrusions, locate open box knockouts by shining a light inside to see where the cables enter the box. That way you’ll know where to inject the foam. Turn off the power and pull the switch or receptacle out far enough to see if you can’t spot the entry points.
  2. Seal the intrusions from outside the box, never inside. Spraying foam inside a box doesn’t meet code, and you’ll have to remove the sealant if it’s ever inspected.
  3. Finish the job by shooting ordinary foam around the box.


Step 4

Cover the Mess With Bigger Electrical Cover Plates

If your caulking/foaming job got out of hand and extends beyond the wall outlet covers, you don’t have to repaint the wall to cover your tracks. Just buy a “jumbo” cover plate.

Step 5

Seal Recessed Wall Boxes: Add a Box Extender

  1. Unscrew the switch or receptacle and twist it at an angle.
  2. Then slide the box extender over the device and into the wall box.
  3. Remount the device, straighten it and then tighten the screws.
  4. Seal the wire intrusion following the procedure above.
  5. Turn off the power (test wires with a voltage tester) and slide on a box extender. Now you’re ready for outlet insulation.


Step 6

Seal Around the Box Extender

For better outlet insulation around box extenders, squirt caulk between the box extender and the wall. Smooth the caulk bead with a wet finger, then seal the gap around the box extender.

  • Pro tip: Sometimes wall-mounted electrical boxes are recessed because of an installation error or new tile installed over the old layer. You can seal around the gap with caulk, but that doesn’t solve the problem of the box not being flush with the wall. That’s where a box extender comes in handy. It provides solid mounting for the switch or receptacle and makes the box easier to seal.

Step 7

Fix Leaky Can Lights

If you have older recessed lights in a ceiling under an attic space, you’re likely losing a lot of heat through the holes in the housing and around the base of the fixture. However, caulking those openings or covering the fixture with an airtight box can create a fire hazard.

The easiest and best solution is to buy an airtight LED retrofit light/baffle kit. Just remove the bulb, screw in the threaded adapter and snap the LED unit in place. No more air leakage.

Up next, here’s what you need to know about smart light switches.

Author
Chris Deziel
Chris Deziel is a freelance service journalist who worked in landscaping and home improvement for more than thirty years. He has published over 10,000 how-to and expository pieces on home improvement and nature topics since he began writing in 2010. Deziel lives and works in an off-grid home in California where he enjoys recording original music an...
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Chris Deziel