furnace leaking water on basement floor

A furnace leaking water is troubling, but it’s not necessarily a reason to panic. It might seem odd that a heating appliance would expel water, but furnace water leaks are common. Since some furnaces generate condensation and add moisture to the air with humidifiers, furnace leaks aren’t that surprising.

Leaks are inconvenient and usually signal minor problems, but they can become big problems if left untreated. Contacting an HVAC company to diagnose the issue and repair the leak is your best option, but homeowners can take steps to minimize the damage. In some cases, homeowners can resolve the problems themselves. Either way, it’s essential to get to the bottom of why your furnace is leaking.

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Reasons for a Furnace Leaking Water

Water leaking from your furnace can be caused by a condensation leak, faulty heat exchanger, or clogged air filter. However, the puddles near your furnace might have another source, such as your humidifier, air conditioner, or plumbing.

clogged high efficiency furnace  condensation pipe

Condensation Leaks

High-efficiency furnaces possess a secondary heat exchanger to extract heat from the exhaust gasses, which is one reason they are more efficient. The cool exhaust gasses produce condensation. The moisture is directed into a drain line that empties into a floor drain.

One of the disadvantages of high-efficiency furnaces is issues resulting from condensation. Clogged dirt and debris in the drain hose, drain line, or condensate trap cause water to leak. Nothing may be wrong with the line; it may have simply disconnected. Broken condensate pumps and cracked pipes, however, must be replaced.

You can try flushing a clogged line with equal parts white vinegar and hot water. Repeat the process several times if needed.

How do I know if I have a high efficiency furnace?

New homes generally have high-efficiency furnaces. Older homes with outdated appliances often have standard-efficiency furnaces. Find the yellow EnergyGuide label on your furnace. High-efficiency furnaces have AFUE ratings of 90% or higher. Check the exhaust pipe. High-efficiency furnaces have white PVC plastic pipes, and standard-efficiency furnaces have metal pipes.

rusted and crack furnace heat exchanger

Malfunctioning Heat Exchanger

Condensation leaks can result from a malfunctioning secondary heat exchanger. High-efficiency furnaces possess both a primary heat exchanger and a secondary heat exchanger to extract more heat from the fuel. Standard-efficiency furnaces only have one heat exchanger.

Primary Heat Exchanger

The primary heat exchanger is located near the burners. It extracts heat from the burning gas. The primary furnace heat exchanger is more prone to cracking since it is situated near the flames and receives more stress.

Secondary Heat Exchanger

The secondary heat exchanger extracts additional heat from the exhaust gasses, which would otherwise be wasted. The cooling gasses result in the formation of condensation. A faulty secondary heat exchanger might cause a condensation leak.

If the leaking condensation results from a malfunctioning secondary heat exchanger, the part will need to be replaced by an HVAC professional. Heat exchanger issues are expensive. According to HomeAdvisor, replacing a heat exchanger costs an average of $1,500. In some cases, the entire furnace needs to be replaced.

dirty air filter in furnace

Dirty Air Filter

The air filter captures dust, dirt, and other debris flowing through your HVAC system to provide cleaner air. How often to change an air filter depends on different factors, but they need to be changed regularly to keep the air flowing. Clogged filters restrict airflow and can cause the furnace coil to freeze.

The furnace coil, also called the evaporator coil or the A-frame coil, is a component of split HVAC systems that provide heating and cooling. Some coils are located in the air handler; others are located inside the furnace. When your air conditioner runs, the coil extracts heat from warm air blowing across the coil to cool your home. When your furnace runs, warm air also blows across the coils, though the coil doesn’t absorb any heat.

Warm air is cooled by the cold refrigerant flowing through the coil while the air conditioner runs. A clogged filter restricts the airflow, which can cause the coils to become too cold and freeze up. The ice melts and drips onto the floor beneath the furnace when the air conditioner shuts off.

Swap out a clogged filter for a new one, and change the filter regularly to keep the flow of air unrestricted.

broken whole house humidifier on furnace

Broken Humidifier

Whole-house humidifiers attached to furnaces use water to add moisture to dry, heated air. Water can leak from lines that are cracked or poorly fitted. The humidifiers’ excess water is channeled into the furnace drain line. A clog in the drain line can cause water to build up until it leaks from the humidifier. Call an HVAC professional to prevent water damage and mold growth.

basement plumbing line causing leak in basement

Plumbing Leak

The leaking water may not be coming from your furnace; it might be a plumbing leak. A plumbing pipe located near your furnace could be damaged or clogged. The good news is that minor plumbing issues are often cheaper than furnace issues. Call a plumber or an HVAC technician to diagnose and fix the problem.

leaking air conditioner condensate pan

Leaking Air Conditioner Unit

Air conditioning units contain condensate pans to collect moisture from the evaporator coils. A clogged pan can cause water to overflow onto the floor. If you have recently been running your air conditioner, a clogged condensate pan might be the issue. If your air conditioner is leaking water, the pan needs to be drained and the clog removed. You can attempt to resolve this issue yourself or call an HVAC technician.

Is Water Leaking From Furnace Dangerous?

Is a furnace leaking water dangerous? Water leaks are more damaging than hazardous. Leaks cause rust formation, mold growth, and damage to electrical components, walls, and floors. Leaks should be addressed immediately to prevent more costly repairs down the road.

What to Do if Your Furnace Is Leaking Water

Call an HVAC technician if your furnace is leaking water. A furnace professional will diagnose the problem and offer a solution. In the meantime, here are actions you can take to minimize the damage and potentially solve the problem yourself:

  1. Turn off the furnace to stop the water and protect yourself from electrical shocks. The furnace can be turned off at the thermostat, the switch on the furnace, or the circuit breaker.
  2. Dry water that has pooled on the floor with towels, a mop, or a wet-dry vacuum.
  3. Dry water drips inside the furnace if you are comfortable doing so. Unscrew and remove the access panel. Use a towel to dry any drips you can see.
  4. Check the air filter, and replace it if it’s dirty or wet.
  5. A clogged condensate line can be flushed with equal parts white vinegar and hot water. Repeat the process several times if needed.

Regular furnace maintenance inspections can prevent leaks and other issues from occurring in the future.

Frequently Asked Questions

Why do high efficiency furnaces condensate?

High-efficiency furnaces condense when the secondary heat exchanger extracts heat from the exhaust gasses. As the exhaust cools, condensation forms. According to HomeTips, condensing furnaces produce five to six gallons of condensate a day.

Why is the furnace leaking water when ac is on?

Pooled water around your furnace might result from air conditioner issues. Condensation from the air conditioner might pool near the furnace from a loose or misaligned drain line, a clogged or cracked drain pan, a clogged air filter, or malfunctioning evaporator coils.

Why does my furnace exhaust gurgle?

Gurgling and dripping sounds from a high-efficiency furnace usually indicate issues with condensation drainage, such as a clogged drain line or broken condensate pump. Gurgling sounds from the vents or ducts might indicate more serious moisture issues.

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