Gas Furnace Vent Pipe Leaking Water? Here’s What’s Really Going On

So, you’re checking your basement and notice water dripping near your gas furnace vent pipe. Maybe there’s frost on your PVC vent pipe in winter, or you’ve got a weird musty smell coming from the furnace. Yeah… that’s not normal. Let’s break down why this happens and what you can do before it turns into a $1,000 headache.

Why Furnace Vent Pipes Leak Water (Condensation Explained)

High-efficiency gas furnaces are awesome at keeping your home warm, but they produce a LOT more moisture than older furnaces. When the hot exhaust air hits the cold vent surface, condensation forms. If your vent has:

·Long horizontal runs

· Too many elbows (especially 90° bends)

· Improper slope

…water will start pooling in the high points or elbows. In winter, that can even freeze and cause leaks or cracks.

How to Spot Trouble Early

Here are the warning signs your vent pipe is leaking:

Water puddles or dripping near the furnace or basement wall

Frost or ice forming on the PVC vent in cold weather

Musty or damp smells from standing condensate

Rust or discoloration around fittings

If you notice any of these, don’t wait. Ignoring it can damage your furnace or even trigger mold growth.

Quick DIY Fixes (That Actually Work)

Check the slope: Vent pipes should drop at least ¼ inch per foot toward the furnace or condensate drain.

Clear the drain: Make sure your condensate drain isn’t clogged. Standing water = trouble.

Install a PVC vent cap with stainless steel mesh: This keeps leaves, debris, and insects out, while letting condensation drain properly. Easy to install and highly effective—like this PVC Vent Cap with 90° Elbow.

Insulate vent pipes: Cold spots create condensation. Wrap exposed PVC in insulation sleeves.

Call a pro if needed: Sometimes DIY isn’t enough, especially if the vent is complex or water keeps backing up.

Pro Tips to Avoid Future Leaks

Schedule annual furnace maintenance

Keep intake and exhaust vents free of debris

Use corrosion-resistant materials (PVC or stainless steel)

Check for ice or water after heavy cold snaps

 

Pro Tip: A simple PVC vent cap with a 90° elbow and stainless steel mesh can prevent 90% of these water leaks. It’s a small upgrade that saves you from major headaches down the road.