A Water Leak In Your Furnace? It's More Likely Than You Think

Posted on: 7 May 2015

You'd think water leaks would be the sole province of faulty plumbing, but it can happen to HVAC systems as well. So it might seem a little strange seeing your furnace spring a water leak around its base. But when you learn the reasons of why a unit devoted to heating your home would leak water, it begins to make sense.

The following offers an in-depth guide on pinpointing the causes of furnace water leaks, as well as some tips on plugging those leaks for good. Check it out!

Condensate Leaks Caused by Your Furnace

Furnaces are the last appliance you'd expect to produce water as a byproduct, but it's not so far-fetched if you happen to own the latest high-efficiency furnace. Featuring an Annual Fuel Utilization Efficiency (AFUE) rating of 90 percent or better, these furnaces are designed to extract a greater amount of heat from combustion gases than a typical conventional furnace.

While a conventional furnace allows still-hot combustion gases to escape through the flue, a high-efficiency furnace so thoroughly extracts heat from the gases that they cool down and condense the moisture within into liquid form. This condensation usually exits out of the furnace through a drain, but a clogged or broken condensate drain line can prevent that from happening.

Fortunately, there are a few ways to get to the heart of the problem and fix it for good:

  • Visually inspect the drain lines for cracks, pinholes or other signs of wear and/or deformation. Damaged condensate drain lines may need to be replaced.
  • Check the lines for any blockages. Dirt, mold growth and other debris can clog up drain lines, leading to condensate spillover.
  • Relieve blockages with the help of a powerful shop vacuum or a blast of compressed air. If there's a condensate drain tray in use, it's a good idea to give it a thorough cleaning.
  • If your HVAC system comes with a built-in humidifier, make sure it's not cracked and/or leaking water.

If this doesn't solve the problem, then you might want to have your HVAC technician take a look at your furnace's secondary heat exchanger. A cracked or otherwise damaged heat exchanger could allow condensation to collect and eventually spill out of the furnace.

Condensate Leaks Caused by Your A/C Unit

Most homes feature an integrated indoor HVAC unit where the air conditioning portion resides on top of the furnace portion. In most cases, the A/C and furnace portions may also share a single blower fan and other assorted components. This arrangement not only saves space, but it also helps keep maintenance costs at reasonable levels.

As you operate your air conditioner, the removal of latent heat facilitated by the A/C's evaporator coil also causes moisture within the air to condense. This condensate usually lands in a collection tray, where it drains away from the unit through a series of drain lines. If one of these lines becomes clogged with debris, the tray could overflow with condensate, which would then spill over onto the furnace and its surroundings.

The above measures used to prevent condensate leaks in furnaces can also be put to good use for air conditioner-source leaks. For A/C units, you can keep those condensate lines clear by pouring a whole cup of bleach into the drain line. Bleach's disinfecting properties will help keep mold growth at bay between periods of regularly scheduled maintenance.

In addition, you may want to consider the role your home's humidity plays when it comes to moisture and condensation. In humid climates, you can use a dehumidifier to help bring down indoor moisture levels and reduce the amount of condensation your furnace and A/C system has to deal with.