Understanding Venting & Condensate “Code Gotchas” for 90% Furnaces in the Wiregrass

High-efficiency gas furnaces—often called 90% furnaces or condensing furnaces—are becoming more common in homes across Dothan, Headland, Ozark, Enterprise, Daleville, Ashford, Kinsey, Taylor, and the surrounding Wiregrass area. These systems offer excellent energy savings and quieter operation, but they also come with special installation requirements that standard furnaces don’t have.

When those requirements aren’t followed correctly, homeowners can face water leaks, furnace shutdowns, corrosion, unsafe venting, mold risks, code violations, and expensive repairs—often years after the installation was done.

This is why understanding proper venting and condensate management is so important. Even if you’re not the one installing the furnace, knowing the basics helps you protect your home and ensure your system is running safely and efficiently.

In this week’s Eco Heating & Cooling blog, we break down the most common “code gotchas” we see in the Wiregrass area when it comes to 90% furnaces—and how to avoid them.

What Makes a 90% Furnace Different?

A 90% furnace uses technology that captures more heat from the fuel it burns, which means less heat escapes through the exhaust. Because of this design:

• The furnace produces cooler exhaust, so it cannot use a metal flue like older furnaces.

• It creates condensation (condensate)—a byproduct of pulling extra heat out of the exhaust gases.

• It must use PVC venting and a safe, code-compliant drain system for the water.

That water isn’t a small drip—some homes produce gallons of condensate per day during heating season. If it isn’t handled properly, it can leak into floors, attics, insulation, and walls.

This is where the “gotchas” come in.

Why Homeowners in the Wiregrass Need to Pay Attention

In the Dothan area, homes with gas heat often have:

• Furnaces in attics

• Long vent runs

• High humidity

• Older drain systems

• Mixed building code enforcement

All of these increase the risk of problems when a 90% furnace is installed or replaced.

Many homeowners don’t know their furnace even creates water until something goes wrong. By then, they’re dealing with:

• Sheetrock damage

• Mold growth

• Corrosion inside the furnace

• Drain backups

• Safety shutoffs

• Failed home inspections

• Voided manufacturer warranties

When installed correctly, 90% furnaces are extremely reliable. When installed incorrectly, the problems compound quickly.

Common Venting Code Issues (“Gotchas”)

These are the issues Eco Heating & Cooling sees most often during inspections, repairs, and replacements in the Wiregrass:

1. Using the Wrong PVC Pipe or Fittings

90% furnaces require specific venting materials rated for flue gas temperatures and condensate exposure.

Common mistakes include:

• Using plumbing-grade PVC that isn’t rated for flue gas

• Improper glues or primers

• Wrong pipe thickness

These may pass a quick visual check but fail long-term—leading to pipe warping, leaks, or vent blockages.

2. Incorrect Vent Slope (One of the BIGGEST Gotchas)

Condensing furnaces require a ¼” rise per foot so condensate flows back into the furnace and drains properly.

We often see:

• Vents installed perfectly level

• Vents sloping the wrong direction

• “Bellies” or dips that trap water

When water gets stuck in the vent, the furnace can:

• Short cycle

• Lock out

• Corrode internally

• Produce unsafe combustion conditions

This is one of the top failure points in DIY installs and even in some contractor jobs around Dothan.

3. Improper Termination Outside the Home

A vent termination that is too close to windows, doors, or ground level can cause:

• Exhaust re-entering the home

• Icing on the pipe in cold snaps

• Furnace shutdowns when leaves, dirt, or pests block the outlet

Local codes and manufacturers require very specific distances and heights, and in areas like Wicksburg, Midland City, and Ashford—where high winds and heavy rain are common—improper termination can cause severe issues.

4. Missing or Incorrect Intake Venting

Many 90% furnaces use two-pipe systems: one for intake air and one for exhaust.

If the intake pipe:

• Pulls air from a dusty attic

• Is too close to the exhaust

• Isn’t sealed

• Isn’t sized correctly

…it reduces efficiency and can lead to combustion problems.

In the Wiregrass, where attics get extremely hot, incorrect intake venting can cause major performance issues.

Common Condensate Drain Code Issues (“Gotchas”)

5. No Condensate Trap or an Improper One

The trap prevents gases from escaping and ensures water drains properly.

Without it, you may see:

• Water overflowing inside the furnace

• Nasty odors

• Safety switches tripping

• Rusting and corrosion

Some installers skip traps entirely to “save time,” which causes long-term damage.

6. Drain Line Not Sloped Correctly

Horizontal runs must slope downward just like plumbing drains.

When they don’t:

• Water pools in the line

• Algae grows

• Slime forms

• The furnace shuts down

Here in the humid Wiregrass region, biological growth inside condensate lines happens much faster if the slope is wrong.

7. Not Using a Condensate Pump When Required

In many homes—especially attics—gravity alone cannot move the water out of the system.

When a pump is needed but not installed, you’ll see:

• Water backing up into the furnace

• Ceiling leaks

• Mold in insulation

This is extremely common in Dothan and Enterprise homes built before the 2000s.

8. Not Protecting the Drain from Freezing

While the Wiregrass doesn’t get extreme winters, freeze events happen every year—and a frozen condensate drain means:

• A flooded attic

• A cracked drain line

• A furnace that will not run until thawed

Pipe insulation and proper routing are a must.

How Poor Venting & Condensate Setup Affects Homeowners

Even if you’re not an HVAC professional, these issues matter because they directly affect:

✔ 

Safety

 – Improper venting can cause dangerous conditions

✔ 

Comfort

 – A furnace that short cycles won’t heat well

✔ 

Energy costs

 – Efficiency drops when venting isn’t correct

✔ 

System life

 – Water damage destroys furnaces from the inside

✔ 

Home value

 – Incorrect installations fail home inspections

✔ 

Warranty coverage

 – Manufacturers deny claims for improper venting

A furnace is a major investment. The installation details matter as much as the equipment itself.

How Eco Heating & Cooling Protects Wiregrass Homeowners

At Eco Heating & Cooling, we follow:

• Manufacturer installation manuals

• Alabama mechanical code

• Local county requirements

• Best practices for high-efficiency HVAC systems

Every 90% furnace installation includes:

• Correct PVC venting, slope, and glue

• Proper vent termination distances

• Intake setup for safe, clean combustion

• Full condensate trap and drain commissioning

• Anti-freeze protection if the system is in an attic

• Condensate pump installation where needed

• Safety switch testing

• Combustion analysis to ensure the furnace is burning safely

Our goal is simple: protect your home, improve your comfort, and prevent problems before they start.

Need a Furnace Inspection or Upgrade? We’re Here for You.

If your home in the Dothan or Wiregrass area has a high-efficiency furnace—or you’re thinking of upgrading—now is the perfect time to ensure it’s installed safely and according to code.

Call Eco Heating & Cooling for:

• Furnace inspections

• New system installations

• Second-opinion evaluations

• Furnace maintenance

• Emergency service

📞 Call Today: Eco Heating & Cooling

Proudly serving Dothan, Headland, Ozark, Enterprise, Daleville, Kinsey, Taylor, Wicksburg, Abbeville, and all Wiregrass communities.

Licensed • Insured • Local Experts (AL 15172)