Anonymous wrote:By code it's interior space and must be heated and cooled.

My understanding is that code requires only heating.

By code it's interior space and must be heated and cooled.

I added a vestibule but without an interior door. I was told it should have at least heating. We ended up extending a duct to have heating and cooling. It would probably have been fine without it since the interior temperature would condition it given that it's open. In your case, it is closed, and it really depends whether you see it as basically an enclosed porch (which will indeed get pretty cold and warm during summer/winter) or as a "living space" area. If the latter, then you should extend a duct. If no duct, at least heating

Yes - ours doesn’t and then no one wants to go in it 9 months out of the year and it makes it useless

We have an unheated vestibule and in winter frost forms on the interior walls even though it is an insulated space. You should have some heat if it gets very cold outside in your area.

If it didn't have an interior door, you could probably do without. But with an interior door it would be best to have it. Try to connect to an existing duct nearby.

Yes, you do. It will become like a little greenhouse in the summer.

Yes you need this

As part of a major renovation to our 1930s colonial we are adding a front vestibule. There will be an exterior door and then on the other side of the vestibule, an interior door. Our architect's view is that the vestibule should have heating and an AC duct. To me this sounds crazy, all the old houses with vestibules do not have separate heating and cooling for that area. But, I do recognize that this is an addition and we live in DC in the 2020s where it gets mighty hot during the summer. Thoughts?