I'm planning to install several temperature sensors in my hot-air furnace's ductwork, specifically in the return duct and in the supply plenum of each of our two furnaces. The sensors I plan to use are 7mm in diameter; I'm looking for a way to get them into the ducts without a) leaking air and b) looking crappy.
So far, my best thought is a 5/16" or 3/8" hole drilled and sealed up with foil ("real") duct tape; are there other ways that might be cleaner-looking?
This is mostly a "because it seems cool" project; planning to use a Raspberry Pi to capture the data and add it to a small home status dashboard I have set up. It will also give some insight into how the furnaces and A/C are performing.