Clear the Air: Venting and Intake Best Practices for 5-Ton R-32 Gas Furnace Combos

🔧 Tony’s Intro: Let’s Talk About What’s Coming and Going

Alright, let’s get something straight right outta the gate—your furnace doesn’t just blow hot air. It’s breathing in combustion air, pushing out flue gases, and depending on how you vent it, it could either run smooth or become a constant callback.

Over the years, I’ve seen it all—pipes pitched the wrong way, intakes pulling from the attic, exhausts dumping onto patios, and don’t even get me started on those sloppy wall penetrations. And when it goes bad? You’re dealing with shutdowns, error codes, carbon monoxide risks, and the kind of draft problems that’ll have your customers calling at 2 a.m.

So today, I’m walking you through everything you need to know about venting and intake best practices when you’re installing one of these Goodman 5-ton R-32 AC and gas furnace systems. We’re talking PVC sizing, vent lengths, air source options, clearances, troubleshooting airflow codes—you name it. I want you walking into that install with a plan and walking out with zero callbacks.

Let’s pop that panel and dig in. 🧢

 

🛠️ Know Your System: What You’re Dealing With

A typical 5-ton combo system from the R-32 AC and Gas Furnace Collection includes a high-efficiency 96% AFUE furnace like the GR9T961205DN. That means it’s a condensing furnace, which requires two-pipe venting: one for intake, one for exhaust.

If you're new to this, condensing furnaces extract extra heat from combustion gases. That’s great for efficiency, but it also means lower exhaust temps, so you can’t use metal vent pipe anymore. You’re in PVC territory now, and that opens up a new set of rules.

The best place to get familiar with this is the International Residential Code (IRC). It lays out the minimum requirements for vent clearances, pipe pitch, and approved materials.

 

📏 PVC Pipe Sizing and Material Tips

Alright, let’s talk plastic. When you’re working with a 120,000 BTU Goodman furnace, you’re looking at either 2-inch or 3-inch Schedule 40 PVC depending on total equivalent length and the number of elbows.

Here’s a cheat sheet I use on jobs:

• Up to 50 ft with few elbows? 2-inch works fine

• 50–100 ft or more than 4 elbows? Go 3-inch

• Always slope the exhaust pipe ¼ inch per foot back toward the furnace

• Intake pipe can be level, but I still slope it out just in case of condensation

The manufacturer’s install guide (which should be stapled to your forehead) gives exact limits. You can also double-check against ASHRAE's ventilation standards.

And don’t glue things together until you test fit everything. Dry-fitting is your friend.

 

🌪️ Intake Air: Where and How to Pull It In

Now for the other half of the equation—intake air. If you mess this up, your furnace won’t burn clean. Worse, it could trip out on pressure switch or flame rollout errors.

Best practice? Pull combustion air directly from outdoors, using a dedicated intake pipe. It makes the system sealed, safe, and much more efficient—no attic dust, garage fumes, or depressurized rooms messing up the burn.

Ideal intake placement should be:

• 12 inches above grade minimum

• At least 3 feet away from exhaust terminations

• Nowhere near dryer vents, chimneys, or fuel tanks

• On the same wall as the exhaust, but not directly next to it

If you’re not sure how far apart your pipes need to be, check this guide from Building America Solution Center, backed by the U.S. Department of Energy.

 

🚫 Common Venting and Intake Mistakes to Avoid

Here’s where I see a lot of guys trip up:

• Exhaust pitched the wrong way—condensate ends up outside instead of draining back

• Pipes too close together—which lets exhaust re-enter the intake

• Long horizontal runs with no supports—PVC will sag and cause water buildup

• Using cell-core PVC, which isn’t rated for combustion use (use Schedule 40 solid-core only)

One of the worst mistakes? Terminating intake inside the home or garage. That’s a code violation in just about every state and a major safety issue.

If you're ever in doubt, the International Code Council is your go-to for proper clearance tables and material specs.

 

🧪 Testing and Verifying Combustion Airflow

Once you’ve got everything hooked up, don’t assume it’s good just because it looks nice. You need to verify combustion using a draft gauge and combustion analyzer.

Here’s my quick checklist:

• Test draft pressure at the pressure switch port

• Check CO and O2 levels in the flue with analyzer

• Confirm flame stability during blower operation

• Inspect for condensate backup and verify trap operation

And yes, always install a proper condensate trap and slope it right. If the water backs up into the heat exchanger, you’ll be looking at a rusted-out furnace in a couple of years.

 

🧰 Troubleshooting Airflow and Venting Errors

So let’s say something’s off. The furnace is short cycling, flashing codes, or just not firing right. Here are the most common issues I run into:

Error Code: Pressure Switch Open

• Blocked intake or exhaust

• Sagging pipes full of water

• Clogged condensate trap

• Cracked or kinked pressure switch tube

Error Code: Flame Loss

• Improper vent termination recirculating exhaust

• Weak draft due to pipe length or elbows

• Combustion air source drawing in contaminants

• Burner orifice partially blocked

Keep Goodman’s diagnostic guide handy on your phone. I can’t count how many times it’s saved me from pulling my hair out.

 

🏠 Tips for Retrofit Installs in Existing Homes

If you’re replacing an 80% furnace with a 96% unit, you’ll need to run new PVC venting. Don’t reuse that old metal B-vent—it’s not compatible with condensing systems.

Here are my retrofit best practices:

• Plan the shortest possible vent path to the outside

• Check attic or crawl space clearances before cutting anything

• Seal wall penetrations with foam and secure pipe clamps every 4 feet

• If running vertical, use concentric vent kits to save wall space

I like to walk customers around the outside of the home and explain where vents will terminate—keeps surprises to a minimum when you start drilling holes in their siding.

 

🧠 Wrapping It Up with Tony

Look, venting and intake might not be the flashiest part of the job—but I’ll tell you right now, it’s one of the most important. Do it wrong, and even the best furnace in the world is gonna throw errors, run dirty, or worse, shut down when you need it most.

But if you follow best practices, use the right pipe, test everything twice, and stick to code, you’ll be giving your customers a setup that burns clean, runs quiet, and lasts for years.

If you’re looking for a matched system that’s vent-ready and built for performance, you can check out the full lineup of Goodman 5-ton R-32 AC and gas furnace combos over at The Furnace Outlet. They’ve taken care of the hard stuff—sizing, compatibility, model matchups—so you can focus on the install and knock it out right.

Need even more information on airflow issues? Visit my guide: Choked Air.

That’s it from me for now. Keep those flue pipes sloped, your pressure switches happy, and your customers warm. Catch you next time I’m elbow deep in a furnace.

—Tony the Trusted Tech 🧢