I went up in my attic again, and now I’ve got a plan. I think I should be able to run the coax cable for the HDTV antenna down through the hole where the duct for the fireplace smoke goes. Anyone want to help? :-)
I’m not quite sure yet how to get the cable out of the wall at the fireplace, but I have a feeling it will involve taking apart the fireplace and getting very sutty. I’m thinking it might be a good idea to run a long piece of conduit down the hole, then slide the cable through that. But it looks like it’s straight up and down, and pretty wide. So that’s promising.
And for my reference, my furnace is model THP 050A 935AZ.