Furnace is condensing

[Ernest D]

When changing my furnace filter I noticed a small pool of water on the floor. The furnace is a 12-year-old high-efficiency model used to heat the home through metal ducts. I did not see water during the summer, only after the furnace has been on for a few months.

Is this something to be concerned about?

[home improvement guy]

What you are describing is also known as a condensing furnace. Older, less efficient furnaces simply burned fuel to produce heat inside a heat exchanger. The products produced by combustion, including gas and water vapors, were then sent up and out through a chimney or flue. Some of the heat you paid to produce also went out through the chimney.

A condensing furnace utilizes a second heat exchanger to capture heat from the combustion products. The extra heat from the exhaust is then released to the home before being vented to the outside. When the exhaust loses so much heat, some of the byproducts are condensed back into a liquid and are drained away from the furnace. Sometimes they are drained through the same drainpipe as the air conditioner coil if you have one.

If you see any liquid in or around the furnace during the heating season, the furnace is not draining the condensate properly. Turn the furnace off at the main service switch or at the main electric panel. Remove the front cover of the burner compartment. (The gas pipe enters the furnace at the burner area.) If you notice water, do not touch it as it can be acidic.

There should be rubber hoses, a draft inducement fan and one or two larger plastic PVC or ABS pipes for venting and for the combustion air intake. Wearing protective rubber gloves and without touching any of the hoses, wires or pipes, use paper towels to soak up the condensate water. Properly dispose of the wet paper towels.

Close and seal the furnace cover and turn the electric service to the furnace back on. You have now done all that can be done by a homeowner to one of these complicated high efficiency units. Call a licensed HVAC (Heating, Ventilation and Air Conditioning) technician for assistance to clean, service and replace any damaged equipment. If the water you found appears to be leaking from the PVC condensate drainpipe outside of the furnace, you will want to make sure all joints in that pipe are secure and sealed against leakage. If there are any leaks in the condensate drainpipe, you may be able to repair them yourself with PVC cement.