If you close the door and mark where it rests against the frame, then nail a strip (doorstop or any piece of wood which will fit) where the door will fit against it, you will greatly reduce air infiltration.

Do you think wood would be better than the strip of foam? The latter seems to be sealing the gap really well -- the foam gives a little as the door closes so that I can't see light through there any more.

The thing about foam is that it won't last. I use foam on the outside door in my bathroom to make my showers less unpleasant in the winter, but I have to replace it every year. I'm also getting some rot in that door, which is possibly related.

That's a really good point. We've been sealing around my mom's door every year with it, and miraculously every year it needs to be redone... I guess since we've got it on this year, we'll leave it and try to remember to put something more permanent there next year!

I've yet to see a flexible material that doesn't harden/becomes brittle over the years. Most of those seals are some kind of elastomer. I suspect that the same properties that make those materials elastic also make them more susceptible to environmental damage, either from free radicals or UV radiation.

I guess silicone rubber is probably very good w.r.t. long-term flexibility, but it can be susceptible to mold.

Another issue is that a wooden outside doors need gaps all around for it to be able to dry properly, and to account for the wood shrinking and expanding. A door that fits too closely (especially at the end-grain of the wood) might stay wet longer and rot. So seals should be on the inside face of the door where they are least likely to get wet.

Personally, I prefer pulltruded fiberglass doors/windows and frames. They'll last for decades without much maintenance (no painting!) except for replacing the rubber wing seals occasionally. And since those seals are on the inside, they can last for at least 5-10 years.

I'm sorry to say but the problem appears to be that the jam (the part the door seals against) is missing so there will always be an air leak. With the door closed, make a 1x frame and (evenly) nail it to the door frame within about 1/8th inch of the door to allow installation of weather stripping (to seal it). Put a wiper on the bottom of the door and you're done.

Vester --- true, we could probably add in a jamb like we did on the other side. That might actually be what Daddy was suggesting too...

Roland --- I'll have to keep my eyes open for fiberglass doors at the thrift stores, which is where we got this one. Things do tend to turn up if I know what we're looking for!

The wood door stop is standard. Put the foam on top of it if needed. Here's the deal behind movable openings. Every time air has to go around a corner it slows down tremendously. Making it turn the corner before a final sealant means the sealant can do what it was designed for--a back up, not a first line of defense.

You just sold me with your information about air going around a corner. That makes so much sense!!!