Why Do Furnaces Leak Water?

WhyFurnacesLeak-TSHA-Sep12014Web350Pix.jpgThis is a question we get asked a lot, and there’s a good chance that you’ve wondered about this yourself. Let us begin by saying that although a leaking furnace is common, it is NOT okay. It is signaling that something needs adjusted, serviced, or replaced.

We’ll give you a bit of foundational information first, to help make better sense of it. Heating, ventilation, and air conditioning systems (also known as HVAC) are comprised of many elements that operate together to keep your home’s air clean and comfortable. To be very simplistic about it, these systems essentially work along these lines:

~ Temperature is controlled by the thermostat

~ Furnaces heat the air in the winter

~ Blowers circulate the air throughout the home

~ Air conditioning evaporator coils remove heat and humidity in summertime and condensate lines carry the extra moisture to the floor drain

~ Air returns to the furnace for conditioning, humidity is added in, and the air is cleaned before being recirculated

Although the system is definitely far more intricate than this, leaving plenty of opportunity for malfunction, there are really five main possibilities for a leaking furnace.

1) Broken or clogged line in a high efficiency furnace – Furnaces with an Annual Fuel Utilization Efficiency (AFUE) rating of greater than 90% produce condensation as a result of cool exhaust. The condensation on these furnaces is typically carried to a floor drain via PVC tubing, which can experience clogs or line breaks, thus causing leakage.

2) Improperly sized flue pipe in a standard efficiency furnace – Standard efficiency furnaces have metal exhaust pipes and should NOT have condensation. If it does, it likely means that the flue pipe was not sized correctly. The hot exhaust is probably cooling down and condensing in the pipe, then draining back to the furnace where it leaks out. Leaking is a bit more worrisome in the standard efficiency systems since they should not have condensation.

3) Clogged internal drain system – If your air conditioning unit and your furnace share an internal drain, and your air conditioning unit is still operating, it could mean a clog in your internal drain system. This clog would send water to the furnace, causing leakage.

4) Furnace humidifier issue – It’s possible that your humidifier is leaking inside your furnace. Usually, this is something that is caught in your annual HVAC service check, but if you tend to skip those, the leak can go unnoticed for too long and cause an unseemly amount of internal damage to your furnace. Don’t skip those.

5) Faulty furnace secondary heat exchanger – The secondary heat exchanger may be the water source around your furnace if you don’t have a condensation issue. This is one of the least favorable possibilities, because it usually means a pricier fix or a complete furnace replacement.

As with any information we share, we hope that you find it educational and helpful, but we do encourage you to seek the help of an industry professional should you encounter an issue with your HVAC system. Letting leakages go too long can cause extensive and pricy damage, including complete furnace replacements, warped floors and walls, and mold growth.