Homeowners are often surprised when their fairly new high-efficiency furnace shuts down unexpectedly in the middle of winter. In many cases, the problem is due to ice build-up in the vent pipe, blocking the exhaust flow. In models that are 90% efficient or greater, the lower temperature of the exhaust can allow moisture (a by-product of combustion) to condense in the flue, especially when outdoor temperatures drop into the 20’s or below.

High-efficiency (or “condensing”) furnaces exhaust the combustion gases and bring in fresh air through white plastic PVC pipes, usually routed to the outside through the sidewall of the house. If not installed correctly or checked regularly, problems in these pipes can affect the operation of the furnace itself. (Read more….)