Upgrading your HVAC system isn’t like replacing a toaster. You’re talking about thousands of pounds of equipment, electrical tie-ins, gas line connections, permits, ductwork — and a whole lot of coordination. But don’t stress.
If you’re going with a new 3–5 ton air conditioner and gas furnace combo — especially one using R-32 refrigerant — you’re doing your home a serious favor. Better performance, lower bills, and way better indoor comfort.
But before your old unit gets yanked out and the new one gets fired up, you need to know what to expect.
I’ve done hundreds of installs over the years. Here’s a step-by-step breakdown of how a professional HVAC installation unfolds — from day one prep to final inspection.
📦 Step 1: Pre-Installation Site Visit and Load Calculation
Before any tools come out of the truck, a proper install starts with a home evaluation and Manual J load calculation.
This is where a licensed HVAC contractor measures:
-
Total square footage of your home
-
Insulation quality and window types
-
Local climate zone
-
Number of occupants
-
Duct sizing and condition
This isn’t fluff. Sizing your system wrong is the #1 way to waste money. Oversized systems short-cycle and wear out faster. Undersized units can’t keep up when it matters.
ACCA’s Residential Manual J Guidelines are the gold standard here. If your contractor skips this step or just eyeballs it — show ‘em the door.
Once sizing is confirmed, they’ll help you choose a matched system — typically a 3–5 ton AC unit paired with a 96% AFUE gas furnace. If you’re buying direct, like through The Furnace Outlet, you can already shop for AHRI-rated combos that are perfectly matched.
📝 Step 2: Permits and Prep Work
Next comes the paperwork. Most areas require at least one of the following:
-
HVAC permit
-
Electrical permit
-
Gas permit
Permitting protects you, not just the town. It ensures the system is installed to current codes — especially with new refrigerants like R-32, which follow updated UL safety standards.
Your installer will pull these permits and schedule inspections. You don’t need to be involved — but you should verify they’ve done it.
Meanwhile, your install team will:
-
Order all equipment, line sets, flue pipe, and accessories
-
Schedule delivery and removal of old equipment
-
Book a crane if the condenser is going on a roof (for some 5-ton systems)
-
Block out a full day or two on your calendar
Prep your space by:
-
Clearing furniture or storage around the furnace area
-
Unlocking side gates or crawlspaces
-
Notifying pets and neighbors
🧰 Step 3: Removal of the Old System
On install day, your crew will arrive early with tools, protective mats, and a plan.
They’ll shut off power and gas and begin disconnecting the old equipment. This includes:
-
Recovering the refrigerant (legally required)
-
Disconnecting the flue and vent pipes
-
Removing the condenser and disconnecting the whip
-
Pulling out the furnace, coil, and blower
Depending on age and condition, you might see rusty plenums, collapsed duct boots, or leaky drain lines. Good installers will flag those issues and suggest fixes — not just slap in a new box.
Expect 2–4 hours for a full removal, depending on access.
🧱 Step 4: Furnace and Air Handler Setup
Once the old gear is out, the crew will begin:
-
Placing the new furnace on vibration pads or risers
-
Installing a new drain pan (if required)
-
Reconnecting the plenum or fabricating a new one
-
Installing the coil (cased or uncased) on top of the furnace
-
Connecting the furnace to the existing gas line and condensate line
If you’re switching from an 80% to a 96% AFUE furnace, this is where you’ll see changes. High-efficiency units require:
-
PVC venting (2- or 3-inch pipes)
-
A drain for the condensate line
-
A combustion air intake (sealed combustion)
Don’t be surprised if they drill a hole through the side wall to run the flue. This is standard for 90%+ furnaces and actually makes your system safer and more efficient.
❄️ Step 5: Installing the Condenser and Line Set
Outside, the AC condenser gets placed on a pad or concrete slab. For 3–5 ton systems, that unit can weigh 200–300+ lbs, so they’ll use proper lifting gear.
Installation includes:
-
Connecting the liquid and suction lines (aka line set)
-
Brazing copper joints with nitrogen purging to avoid scale
-
Pressure testing with nitrogen to check for leaks
-
Pulling a deep vacuum (down to 500 microns or better)
-
Charging the system with factory-specified R-32 refrigerant
Here’s where R-32 shines. It requires 30% less charge than R-410A, and since it’s a single-component refrigerant, it’s easier to service and less prone to breakdowns over time.
You can learn more about R-32’s benefits in this breakdown from Daikin.
🔌 Step 6: Electrical and Thermostat Wiring
Your furnace and condenser need power — usually 120V for the furnace and 240V for the condenser. Your installer will:
-
Run new wire or reuse existing (if up to code)
-
Connect the whip and disconnect box for the outdoor unit
-
Wire the thermostat to the furnace control board
-
Program the thermostat for staging, fan control, and energy savings
If you’re upgrading to a smart thermostat (like an Ecobee or Nest), now’s the time. But make sure it’s compatible with two-stage or variable-speed systems if that’s what you’re installing.
Energy Star has a full list of certified smart thermostats that qualify for rebates and save energy.
🔥 Step 7: Start-Up and Commissioning
This is the fun part — seeing your new system come to life.
After everything’s connected, your installer will:
-
Fire up the furnace and test the blower motor
-
Start the AC and measure superheat, subcooling, and static pressure
-
Adjust fan speeds and gas pressure (if needed)
-
Check flame sensor, igniter, and safeties
-
Test airflow across coil and register temperatures
All of this ensures the system runs like it should. A good contractor will give you a commissioning sheet showing all the numbers — refrigerant charge, airflow, temp split — so you know the system’s dialed in.
Don’t settle for someone just flipping a switch and saying “You’re good.” Commissioning is what separates a proper install from a warranty headache six months down the road.
📋 Step 8: Final Inspection and Walkthrough
If permits were pulled (and they should be), the local building department will send an inspector within a few days.
They’ll check:
-
Proper venting and clearances
-
Electrical and gas line connections
-
Condensate drainage
-
Combustion air
-
Manufacturer labels and model numbers
Assuming everything is done to code, you’ll get the green light.
Before the crew leaves, ask them to:
-
Show you how to change the furnace filter
-
Demonstrate thermostat programming
-
Explain what to do in case of a power outage
-
Provide a copy of the AHRI certificate for your records (needed for rebates)
You can also check Energy.gov’s guide to new heating system installations for tips on post-install maintenance.
💰 How Much Time Does It All Take?
Here’s a realistic timeline for a 3–5 ton system installation:
-
1 day for simpler swaps (no duct or flue changes)
-
2 days if you need new venting, ductwork, or extensive electrical upgrades
-
3+ days for full replacements with attic/crawlspace work or structural changes
Plan for your home to be without heat or AC during the install window — and give the crew space to work.
🛒 Where to Get a Properly Matched System
Not all HVAC systems are created equal. A high-efficiency furnace paired with an R-32 AC unit gives you:
-
Faster cooling
-
Better comfort control
-
Lower energy bills
-
Compliance with new refrigerant regulations
-
Future-proof performance for 15+ years
For a fully matched 3–5 ton R-32 AC and gas furnace system that ships fast and installs clean, check out this lineup:
Shop R-32 AC and Gas Furnace Systems – 3–5 Ton
🧰 Tony’s Final Thoughts on HVAC Installation
HVAC installation isn’t just plug-and-play. It’s skilled labor — done right, it delivers 15–20 years of comfort. Done wrong, and you’ll be calling for repairs before the first winter ends.
Here’s my advice:
-
Choose a system that’s properly sized and AHRI-matched
-
Hire a licensed, insured HVAC company with experience in high-efficiency installs
-
Make sure R-32 refrigerant is part of the system — not an afterthought
-
Ask for commissioning data and keep your paperwork for rebates and warranties
You only replace your HVAC system once every 15 years — might as well do it right.
About the Author
Tony Marino is a licensed HVAC tech with 20+ years in the field. He’s installed everything from leaky old oil burners to modern variable-speed gas furnaces and multi-zone heat pump systems. When he’s not on a ladder, he’s helping homeowners make smarter, more efficient HVAC decisions that pay off for years to come.
