Sensing chimney flue


Active Member
I would like to know the position of the chimney flue for two reasons:

1) Remind that it be closed in winter time.
2) Warn if open before whole house fan comes on.

I'm wondering if there is a clean way to sense the flue position. Of course the problem is heat, I suspect that most of the plastic/magnetic sensors will melt. Any ideas on getting this feedback in the high temp environment?

so... i have a fireplace insert, and I know code says that you can't install any construction materials within 2" of the chimney unless they are high-temp rated. Also, you can't penetrate it.

maybe there's an indirect way? air-pressure differential? air-flow meter? Thermal camera?
Where is the flue, bottom or top mount? Mine is an old heavy gauge steel plate that closes against another piece of steel inside the firebox. If I were attempting this on my fireplace; I'd probably try to use that metal-to-metal contact as a big switch by running some high temp wire to each piece. You could probably pack an lot of refractory around the wires in the hot spots to keep them safe(er).

If it's a top mounted flue, then maybe a simple lever-actuated limit switch would suffice.