Checking Vent Temperatures
Not sure if your home heating or cooling system is operating efficiently and within expected limits? This simple diagnostic step can help you find the source of your heating or cooling issues.
Using a probe thermometer, such as a meat or kitchen thermometer, stick the probe into a return vent (sucking air in when system is on) and allow it to completely reach the temperature coming into the vent. It may take a few minutes to fully reach temperature. Now record this temperature and put your thermometer into the supply vent (blowing out air when system is on) and once again allow it to fully reach the temperature of the air coming from the vent.
For heating modes (in winter): Subtract the supply vent (outlet) temperature from the return vent (inlet) temperature. This temperature is called the vent temp rise, and for most furnaces should be around the 40°-70° Fahrenheit mark. For furnaces that are reading higher (70°+), look to increase airflow by either decreasing furnace filter restriction (lower MERV or FPR), opening furnaces vents and ensuring returns aren’t blocked by furniture, or having a licensed HVAC technician increase your blower speed or inspect for additional heating issues. For furnaces that are reading lower (40°-) look to decrease furnace airflow by increasing furnace filter restriction or booking an appointment with one of our NATE-certified technicians to inspect your heating system.
For cooling modes (in summer): Subtract the return vent (inlet) temperature from the supply vent (outlet) temperature. This temperature is called the vent temp drop, and for most A/Cs should be around the 15°-20° Fahrenheit mark. For A/Cs that are reading higher (20°+) we would recommend inspecting furnace filter for excessive dirt or debris build-up or potentially replacing filter with something less restrictive to increase airflow. These less restrictive filters will typically have a lower MERV or FPR/MPR rating. Additional diagnostic steps could include ensuring all vents are open and returns are not blocked for maximum airflow potential. For further cooling issue diagnosis, call our dedicated support team at (657)777-2869. For A/Cs that are reading lower (15°-) visually inspect outdoor unit to ensure it is functioning as expected. On typical A/C systems, signs of function include a spinning fan at the top or front of the unit, and an accompanying humming or buzzing sound from both the fan and compressor motors. If these signs aren’t present, ensure system breaker or nearby disconnect is on and connected. If system has power but cooling still is not reaching expected levels, contact our expert service team for tips and service appointments to inspect and repair problems at (657)777-2869.
