When the roof penetration was make for the installation there could be a gap for the smell of the asphalt to come through. It is the sun tunnel going through an unconditioned attic? They are not air tight so could be drawing in smells from the surrounding areas. If you have access to it in the attic- seal around the penetration through the drywall and the roof with spray foam and see if that works.

Thanks so much for the reply, SawHorse. I went into the attic and don't see anything plastic nearby. The roof cutout seems to be sealed as well. One thing I forgot to mention is that there is another sun tunnel only 5-6 feet away ( 2 bathrooms that are back-to-back) and it is not making this smell; only the one in this particular bathroom is doing it. Today we had a rainy day and there was absolutely no smell, so it's got to have something to do with sun/ heat. I checked the outer and inner rings, the gasket and the tubing. Can't see anything warped or degrading from inside the house. The only thing I can figure is it might be the "bubble" plastic part on top of the sun tunnel degrading (?)

I don't think that is the case. I think it is the roof sealant just off gassing. Should go away in a few weeks. Can you take a photo of the spot where it comes through the roof in the attic and where it goes through the ceiling from the attic?

The tunnel is located very close to the edge of the eaves and it is a very tight space there (about 2 feet; the entire length of the installed tunnel is about 4 1/2 feet). I'll try to get up there tomorrow. Thanks!

My husband installed them 6 years ago. Says he didn't use sealant, but rather flashing and screws that came with the kit.

It just started to smell this year after six years?

Yes. We removed a large Oak tree that was shading the tunnel. We figured it has something to do with the smell (such as a heat/sun problem), but can't figure out why the sun would cause the tunnel to emit this plastic odor. There's no sealant, the outer and inner rings are not warped, the plastic liner was removed upon installation. So we know the problem is heat/sun, but why?

I think it is the roof. If you seal around the top and where it comes through the drywall that will help the smell and reduce air infiltration into your house.

Hey Meg - did you ever figure out a fix for this? I have a brand new sun tunnel that is emitting a faint burning plastic smell once the sun is up, and then strong smelled throughout the house in a 15 minute period each day when the sun is directly overhead, starting to think its when the sun is hiting at just the right angle. I've paid the HVAC company to come out only for them to say its definitely not the HVAC and then realized its only started since the sun tunnel was added. Pulling the sun tunnel cover off the ceiling makes the smell so much worse, contractor has smelled it but dome on roof doesn't appear warped etc.

I had a similar problem. Took the lower diffuser out and found it had melted. The whole lens had distored under high heat. I think the sun must hit at a certain angle and the rigid tube becomes a magnifiying glass