Furnace leakage is a potential factor mainly only if you have a high-efficiency furnace. A standard-efficiency furnace with an AFUE efficiency rating below 90% doesn’t produce enough condensation to be a problem. However, a high-efficiency unit with a rating above 90% extracts extra heat by utilizing a secondary heat exchanger that condenses water from the flow of furnace exhaust gases. These furnaces can generate up to 5 gallons of liquid condensate per day. If anything goes awry in the system that collects that water and then channels it outside or to an indoor drain, furnace leakage may occur.

Here’s where and why furnace leakage may occur in the heating sequence:

  • Condensate produced by the furnace’s secondary heat exchanger flows into a collector box. Any obstructions here — such as the formation of algae or mold — may result in an obstruction that causes an overflow from the collector.
  • The flow of condensate continues from the furnace through a hose and into the condensate drain trap. A defective drain hose or a leak inside the trap itself can cause spillage of water outside the furnace. The condensate drain trap is an important safety component that keeps hazardous combustion fumes from entering the furnace airflow. To ensure safe operation, as part of annual preventive maintenance, the trap should be inspected for leaks and cleaned by a certified HVAC service technician.
  • Condensate flows away from the drain trap through a rigid PVC pipe due to gravity flow or pumped by an electric motor. The connection at the trap or joints in the pipe may be potential leak spots.
  • In most cases, the drain pipe passes through an exterior wall of the house, and condensate drains into the ground outside. If outdoor temperatures drop below freezing, however, ice formation at the end of the pipe may obstruct flow and cause condensate to back up and cause leakage inside the house or trigger an automatic furnace shutdown.

For qualified professional service to diagnose and repair furnace leakage, talk to the heating experts at Mowery Heating, Cooling and Plumbing.