Why Is Water Coming from My Furnace? Understanding the Issue

If you’ve noticed water pooling around your furnace, it’s natural to be concerned. Water around your heating system isn’t normal and usually signals a problem that needs attention. Here’s what you need to know about why this happens and what to do.

1. Condensation from a High-Efficiency Furnace

Modern high-efficiency furnaces (typically 90% AFUE or higher) produce condensation as a byproduct of extracting more heat from the combustion gases. This water is normally routed through a condensate drain.

• Problem: If the drain is clogged, cracked, or disconnected, water can leak around the furnace.
• Solution: Inspect the condensate line and clean it if necessary, or call a professional to fix any damage.

2. Humidifier Leaks

Many furnaces have attached whole-house humidifiers. These add moisture to the air during winter.

• Problem: A leak in the humidifier’s water line can create puddles near your furnace.
• Solution: Check connections and the humidifier pan for cracks. Replace or repair as needed.

3. Air Conditioner Drainage

If your furnace is part of a central HVAC system with air conditioning, water could come from the AC condensation.

• Problem: Blocked or broken AC drain lines can allow water to overflow onto the furnace area.
• Solution: Clean the AC drain line and ensure it’s properly sloped toward a drain.

4. Plumbing or Roof Leaks

Sometimes the water isn’t from the furnace itself. Leaks from pipes, the roof, or nearby appliances can pool around your furnace.

• Solution: Inspect your home for other sources of water, especially if the furnace is in a basement or utility room.

5. Rust or Corrosion

Older furnaces may develop leaks from rusted heat exchangers or internal components.

• Warning: Water here is serious and can indicate the furnace is near the end of its life.
• Solution: Call a licensed HVAC technician immediately. Do not try to operate the furnace if you suspect internal leaks.



Key Takeaways

• Water around a furnace is never normal.
• Common causes include condensate drainage issues, humidifier leaks, or AC drain problems.
• Safety first: Shut off the furnace if there’s significant water and contact a professional.
• Regular maintenance helps prevent water issues and prolongs the life of your system.