I installed a 24 volt indicator lite,(power comes from my 24v transformer that opens my "make up air " on a call for more heat/fans on, in my boiler building) I put it right next to my zone controls/uponor/taco .... that only turns on when the "blower" fans are on ! now I can tell when the fan comes on/off and if I time it-how long it takes to get up to temp from my shop 75" away> ! *** I had a "wood bridge" last nite and it saved me a trip at 5 below to see what the he!! was up / I guess it didn't save the trip but it let me know something was up !!! had a 146 temp in the supply line and 142 in the return....3 hours latter same chit!! wtf ....went out and found a 6" log "wood bridge" with about a gallon size pile of coal cooking the log ! (think teatertoder) the wood was black/charcoal but did not catch fire ...mean while the coal was like the sun ! it (the coal) kept me up to temp even with 270 cfm's of air blowing !