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Why Is My Furnace Leaking Water?
If you find water around your furnace, turn the system off first. A high-efficiency furnace makes condensate, and a clogged drain, trap, or failed pump can cause that water to back up around the equipment. Dunco has helped Lawrence homeowners with heating solutions since 1988, and we can find where the leak is coming from.
First: Do These 3 Things Before Anything Else
Before reaching out to an HVAC professional, it’s important to determine where the leak is coming from and shut off your water before causing permanent damage.
- Turn the furnace off.
- Check for a humidifier leak. If you can see water coming from the humidifier supply line and can safely reach its shutoff valve, turn the water off.
- Protect the floor. Mop up standing water and move anything nearby that can be damaged.
You do not need to open the furnace or take drain lines apart. Those steps belong with a furnace company like Dunco.
Does Your Furnace Even Make Water? (High-Efficiency vs Standard)
A high-efficiency furnace makes condensate while it heats your house. That water leaves through a drain system. If the drain, trap, or pump stops working, water can collect around the furnace.
A standard furnace does not normally make condensate while heating. Water around a standard furnace needs to be traced to another source.
Common Causes of a Leaking Furnace
Depending on where the leak is stemming from, it can tell you what part of your furnace or other water-related equipment needs repair. Some of the most common causes of water around a furnace include:
Clogged Condensate Drain or Trap
If the condensate drain or trap fills with buildup, water cannot leave the furnace and can back up onto the floor. We can clear the blockage and check why it happened.
Failed Condensate Pump
Some furnaces use a pump to move condensate to a drain. If the pump stops working, its reservoir can fill and overflow.
Humidifier Leak
A whole-home humidifier near the furnace has its own water supply and drain. A loose connection, clogged drain, or leaking humidifier can make it look like the furnace is leaking.
Our whole-home humidity solutions cover equipment used to manage indoor humidity. A leaking humidifier still needs its own repair.
Shared AC Drain Backup (Shoulder Season)
Your AC coil may share drainage near the furnace. During mild weather, a backed-up AC drain can leave water around the furnace even when the heating equipment is not the source.
Heat Exchanger Issues (Call a Pro)
If we rule out the condensate drain, pump, humidifier, and shared AC drain, we need to find where the water is coming from inside the furnace. That means opening and inspecting the equipment, which is not a homeowner check.
Water may not be the only problem you notice. Furnace short cycling or your furnace blowing cold air can give us another clue about what the furnace is doing when the leak appears.
| Where and When You See Water | Likely Cause | First Step |
|---|---|---|
| High-efficiency furnace is running | Condensate drain or trap | Turn the furnace off |
| Around the condensate pump | Failed or blocked pump | Turn the furnace off |
| Near the humidifier | Supply or drain leak | Shut off humidifier water if safe |
| During mild weather or AC use | Shared AC drain | Turn the HVAC system off |
| Around a standard furnace | Another leak source | Have the source inspected |
Can I Keep Running the Furnace?
Leave it off until you know where the water is coming from. Water can reach electrical parts and damage the furnace or surrounding materials.
If your furnace smells at startup, especially like electrical burning, keep it off and have it checked.
When to Call Dunco
If the water comes back after you clean it up, schedule furnace repair in Lawrence. We check the furnace and its drainage to find the source before making the repair.
If the leak is coming from a drain or water line outside the furnace, Dunco's plumbing services can handle that work.
Regular furnace maintenance includes checking the equipment and condensate drainage before heating season, before you lose heat in severe cold weather. Schedule an appointment online or call us today for furnace service.
Schedule OnlineFrequently Asked Questions
Is a leaking furnace dangerous?
Water can reach electrical components or damage the furnace and floor. Turn the furnace off and clean up the water. If you smell gas, leave the house and call the gas utility from outside.
How much does condensate repair cost?
We need to find the source first. Cost changes based on the drain, trap, pump, humidifier, equipment access, and repair needed. Dunco gives you upfront pricing after we diagnose the leak.
Why does my furnace leak only when the heat runs?
A high-efficiency furnace makes condensate while heating. If its drain, trap, or pump is blocked or fails, water can back up while the furnace runs. A standard furnace should not normally produce condensate during heating.
Can I unclog the drain line myself?
Turn the furnace off and clean up the water, but do not take furnace drain components apart if you are unsure how they connect. We can clear the blockage and check why the line backed up.
Will water damage my furnace?
It can. Water can damage electrical parts, the furnace, flooring, and nearby materials. Leave the furnace off until the source of the leak is found and repaired.
