Hi, I am looking at a spiral staircase for my house. This would go between a heated, insulated main floor and an unheated ICF basement. Based on floor plan, there's not a great way to enclose this staircase with walls. This means there would be an open space through the floor where the spiral staircase passes. I know heat rises, but I'm still not sure how much heat is transferred. Do you have any experience with this sort of thing? Ideas for other stairs into a basement (which still has an external daylight door) with a small floor plan? Thanks!

Heat doesn't rise- heat moves from warm to cold. But colder air is denser than warmer air, so there will be stratification, with the coolest air sinking to the basement due to it's lower buoyancy. If the column of sinking cool air has low velocity and there are limited paths for not-quite as cool air to rise into the first floor, there isn't going to be much convective air current.

A lot of things can affect convection between the fully conditioned upper floor and the cooler basement, but if the stairwell is the only major hole it's not likely to represent a significant heat load to the first floor, especially if the basement is insulated under the slab as well as the walls, even with modest convection.

Thank you for the reply! Very interesting. I'm imagining now some houses I've been in where lower floors or basements were noticeably cooler, upper floors noticeably warmer, with an open stairwell with no doors. It makes sense that mine could be similar. I'll look into stratification more. & yes it would be the only major hole in the floor.

You may have to enclose the stairwell on one floor or the other. Most areas have adopted energy codes that are probably going to require a barrier between heated and unheated. Depending on how you are classifying your basement(unheated usually means storage, not living area) you may need a fire rated barrier and door...

I don't see mention of your climate. We have an ICF house in upstate SC. We keep the basement door open (for the stupid cat!), and it works fine. Our walk-out basement drops to about 60 F. in the winter, and goes up to about 76 F. in the hottest part of summer. If the cat ever dies, I'll be curious to see what difference keeping the basement door closed makes. I don't think it makes much difference in the winter, but I imagine it does have a small impact during A/C season. Our A/C cost is about 65 cents a day during the hottest part of summer, though, so the difference may be hard to detect.

Thanks Ron- I asked a local expert who said something like the first poster, that he didn't expect much heat loss/gain through the opening, didn't mention anything about it code-wise but I will look into it. And jdebree, climate here is 6B (Montana) . Ty for your reply

I had a home with an open staircase to the basement. The issues I had were during cooling, cool air would settle down to the basement.

I used drapery rods and fabric, sort of a sky light roman shade that slid on tracks horizontally.

So a spiral stair would be more of a challenge to make a shade that could follow the curve of the floor.