years ago there was concern about even TV antennas and especially their pre-amplifiers being mounted anywhere near where exhaust from combustion would possibly make for unfriendly conditions for the electronics when the vapors cooled and became, in effect, acid rain. Our precious stations are so much more expensive and have temperature, humidity and barometric sensors in some cases, right there in the sensor package.
Is this chimney dormant and no longer used?
What is being exhausted? Fuel oil furnace, or natural gas, or even wood from a fireplace?
What about the heat from the exhaust during heating season? I know some natural gas heaters are exceptionally efficient, but look around during sub zero temps to see all the 'steam' rising from chimneys. Is this going to affect the accuracy of your station?
Just playing devil's advocate here.