Energy Savings: Seal Plumbing and Wiring Holes

Updated: Oct. 30, 2023

A rubber plumbing boot seals holes in your siding

FH07NOV_SEAPIP_04-2Family Handyman
Use a rubber roofing boot to seal holes where air conditioning or plumbing lines penetrate the walls of your home.

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Seal up pipe penetrations

Photo 1: Clean out the old seal

Pry out old putty and caulk from around the pipes and wires.

Photo 2: Trim the rubber boot

Cut the rubber plumbing boot to fit on top of the siding and around the hole.

Photo 3: Mount the boot

Fit the plumbing boot over the pipes, then glue it to the siding with 100 percent silicone caulk.

Photo 4: Foam the inside

After the caulk dries, squirt a small amount of minimal-expanding foam into the opening.

Look behind any air conditioner compressor or heat exchanger and you’ll find at least one large hole for plumbing and wiring. It’s usually bigger than it needs to be and sometimes only partially plugged with a large wad of electrician’s putty, making it a good spot for heat to get out and mice to get in.

Make these holes more weathertight and less unsightly with a 1-1/2-in. rubber plumbing boot (available for about $4 in the roofing section in home centers).

Gently work out the putty (Photo 1) to avoid damaging the pipes or wiring. Replace torn or missing pipe insulation. Learn how to replace rotted insulated A/C lines.

Using scissors or a razor knife, cut the roof boot to fit around the hole and to match the width of the piece of siding (Photo 2). Cut a slit in the bottom edge so the plumbing boot will fit around the pipes.

Spread silicone on all four sides of the hole and at the slit at the bottom to completely seal the edges (Photo 3). You may need to tape the rubber to the siding temporarily until the caulk dries.

Let the caulk dry overnight, then partially fill the boot with foam; seal the hole from the inside as well. Use minimal-expanding foam to avoid opening the slit in the rubber boot, and push the tip several inches in so the foam expands into the hole instead of out the top of the boot (Photo 4).

Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • 4-in-1 screwdriver
  • Utility knife
You’ll also need scissors and leather gloves.

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here’s a list.

  • Minimal expanding foam
  • Silicone caulk