furnace fast cycling - thermostat adjustment
i find myself at 6000 ft altitude in northern new mexico. some nights are already getting chilly, a low of 35 three days ago. so...i removed the furnace for cleaning and repair and fabricated a new sheetmetal front which was missing and performs as a plenum for the system. when i fired it up it would "short cycle" that is, quickly bring the air temperature up to the setting on the thermostat, then turn off, sit for a few minutes and do it again ad infinitum.
i did some research on honeywell thermostats and found that they could be adjusted for the heat anticipater index of the furnace. my 32 year old thermostat was quite unlike anything honeywell sells today but poking around i found just such an adjustment. the actual electrical contact is threaded so that it can be moved closer to or further away from a small magnet that holds the contact until the bi-metal coil produces enough force to overcome the magnet's attraction. or to put it more simply, by moving the electrical contacts closer to the magnet, one may increase the difference in temperatures that turn the heater on and off. i aimed for a difference of 5 degrees F. so if i set the thermostat at 70, if turns on the heater and runs it until the temperature reaches 75 and then turns off the furnace. by the way, the temperature continues to rise for a while even after the furnace and fan turns off.
nights have been toasty. i set the thermostat for 70 before i go to bed and reduce it to 60 at bedtime. the heater has been coming on close to dawn. it heats the cabin up to 65 for my coffee and crossword.