High efficiency furnaces use two PVC pipes for venting -- one is a combustion air intake and the other is the combustion air exhaust. These pipes typically vent out the side of your home and not into a chimney like older furnaces. Due to their location, they may become prone to blockages in the winter from snow and ice. If blocked, the furnace may either malfunction and not run or dispense deadly carbon monoxide gases into your living space.
Turn power off to the furnace. Either flip off the circuit breaker or shut the switch off on the side of the furnace cabinet.
Locate your PVC furnace vent pipes. Sometimes this is easier said than done as things can look drastically different outside during a snowstorm or after a large snowfall. Follow the pipes in the basement to the exterior wall, and make some reference notes as to where the pipes are located. Exterior windows and other penetrations may help serve as a clue when locating the vent pipes outside.
Go outside to the location where you believe the pipes come through. Begin to scoop snow out of the way with your shovel. Go slow to prevent both damage to the vent pipes and to ensure snow is not pushed further down into the pipes.
Shovel out an area down to ground level that encompasses several feet around the pipes.
Scoop snow out of each vent pipe with your fingers. Carefully remove the snow a little bit at a time from within the pipe.
Restore power to the furnace. See that it fires up properly. Go outside and place your hand in front of the PVC pipes. If working correctly, you will feel the exhaust pipe expelling air and the intake pipe sucking in air.
Check on the vent pipes throughout the winter -- especially after snowfalls and periods of high winds. Remove snow as necessary to keep the pipes clear.