I have a Schrader wood stove with the pipe that goes vertical through the ceiling and into triple-wall stainless. I have a magnetic thermometer that attaches to the pipe. It gives an ideal temperature ( I think it is 300-400 degrees). My question is at what height above the stove should the thermometer be attached? There were no instructions for the thermometer. I have it 18" above the top now. thanks in advance for any information.