What's the best way to seal gaps around an exterior door frame?

Weatherstripping tape and caulk work best together - use the tape for moving parts (the door itself) and paintable caulk for fixed gaps between the frame and wall. For larger gaps, pack foam backer rod in first, then caulk over it so you use less material and get better results.

Don't skip the cleanup step - old caulk and debris will just trap moisture and cause the new seal to fail faster. After you've got the tape and caulk sorted, make sure the frame itself is actually square and not warped, because even the best sealant won't close gaps caused by a twisted door jamb.

A lot of people forget about the threshold itself - that's where water pools and gaps matter most. Make sure the door sweeps or threshold seal is actually making contact with the floor, because a perfect frame won't help if water's running underneath. Then tackle the frame sides and top with whatever combo works for your gap size, but the threshold is where most problems start.

Most door frame gaps actually come in two flavors - the ones you can see and the ones hiding behind the trim, and they need different approaches. The visible gaps between frame and wall are your main concern for energy loss and water infiltration, so start there. Get yourself a caulking gun with paintable, flexible exterior caulk (acrylic latex works fine for most climates). Before you apply anything, run a utility knife along the existing caulk line to remove the old stuff completely - this is crucial because new caulk won't stick well to dried-out old caulk, and moisture will get trapped underneath and cause rot.

Here's the part nobody talks about: check your door frame for square before you seal it. Grab a level and see if the frame actually sits plumb and level. If it's twisted or settling, caulking won't fix the problem - you might have to shim the frame first or even reset it. Once the frame is actually square, use painters tape on both sides of where you're caulking; it keeps cleanup fast and gives you a cleaner line. Apply your caulk in one smooth bead, wet your finger slightly, and run it along the seam to compress it into the gap. The others are right that weatherstripping tape handles the moving parts (the door edges), but for the frame-to-wall connection, flexible caulk is where your real seal happens.

One thing I'd add: if you're dealing with gaps wider than half an inch around the frame perimeter, you might have settling or installation issues worth investigating before you just pack everything with foam. But for the typical quarter-inch gaps most of us see, caulk alone does the job just fine.

I had this old back door that was absolutely terrible - light would literally come through the gaps around the frame on sunny days, and every winter the cold would pour in. When I finally tackled it, I realized the real issue was that nobody had ever prepped the surface properly. So here's what actually made the difference: strip out all the old caulk and weatherstripping first (a putty knife and some patience goes a long way), then wipe everything down so it's clean and dry. This step alone solved half my problem because old dried caulk just sits there letting air slip past.

Once that's done, measure your gaps. If they're skinny - under a quarter inch or so - you can usually skip the foam backer and just use caulk directly. For anything wider, lay down a foam backer rod first so the caulk has something to grip onto and doesn't shrink away from the sides. Then apply your paintable caulk in one smooth bead. The weatherstripping tape on the moving parts (the door edges themselves) goes on after, making sure it's pressed firm so there aren't any air bubbles underneath.

The part most people mess up is the bottom - check that your door sweep is actually contacting the threshold. I had to replace mine because it was worn down and doing nothing. Water and drafts love finding their way under the door, so even if your frame seals are perfect, a bad sweep defeats the purpose. Take your time with this part because it's the most important gap to get right.