What to Expect During the Installation of a 3–5 Ton AC and Gas Furnace System

👋 Hey There, Homeowners

I’m Mike Sanders, and I’ve been installing heating and cooling systems for longer than I care to count. One thing I’ve learned: no two homes are exactly the same, and no good HVAC install is ever one-size-fits-all.

If you're looking at a 3–5 ton AC and gas furnace system, you're probably heating and cooling a decent-sized home—maybe around 1,800 to 3,500 square feet. That means the installation isn’t something you want to rush or cut corners on. Done right, it can keep your family comfortable for 15–20 years. Done wrong? You’re signing up for uneven temperatures, high energy bills, and costly repairs down the road.

In this guide, I’m going to walk you through what happens before, during, and after the installation. So whether you’re replacing an old clunker or setting up HVAC in a new build, you’ll know what to expect—and what questions to ask.


🧰 Step 1: The In-Home Assessment or Load Calculation

Before any installation starts, a good contractor will come out and measure your home’s heating and cooling needs—what we in the biz call a Manual J Load Calculation. This step is critical. Skip it, and you could end up with a system that’s oversized (short-cycles and wears out early) or undersized (runs constantly and can’t keep up).

What the Technician Will Check:

  • Square footage

  • Insulation levels

  • Window types and orientation

  • Ceiling height

  • Local climate

  • Air leakage (doors, vents, gaps)

Want to see how this works? Energy Vanguard has a solid breakdown of Manual J and why it matters.

Tip from Mike: If your contractor doesn’t do this, or shrugs and says “You’ve got a 4-ton now, we’ll just stick with that,” find someone else.


🔨 Step 2: Permits and Scheduling

Most jurisdictions require permits for HVAC installs, especially when gas lines or refrigerants are involved. A reputable installer will pull these permits for you and schedule inspections with the local building department.

Common Permits You Might Need:

  • HVAC mechanical permit

  • Electrical permit (if panel upgrades or rewiring is needed)

  • Gas line permit

  • Refrigerant handling documentation (EPA Section 608 certified techs only)

Need to verify your city’s requirements? Check your local listings or head to DSIRE for incentive info that often requires permitted installs.

Tip from Mike: If a quote seems too cheap, make sure permits and inspections are included. Cutting corners on code compliance can void warranties—and cause safety hazards.


🏚️ Step 3: Demolition – Out With the Old

On install day, the crew will start by removing your old equipment. This includes:

  • The outdoor AC condenser

  • The indoor furnace and evaporator coil

  • Any refrigerant lines that need to be replaced

  • Old thermostats or air filters if you’re upgrading

If your old system used R-22 refrigerant (which is now banned), techs will properly recover and dispose of it, per EPA refrigerant management rules.

The whole process usually takes a couple of hours, depending on how easy it is to access your attic, basement, or crawlspace.


🔩 Step 4: Ductwork Modifications and Airflow Checks

This is where the rubber meets the road. You can have the most efficient 3–5 ton unit on the market, but if your ducts are a mess, you won’t feel the difference.

Installers Will Check:

  • Duct sizing and balance

  • Air leakage and insulation

  • Plenum size and connection

  • Return air volume

Many homes have ducts that were sized for an older system or hacked together over time. In some cases, we may need to:

  • Replace the main supply trunk

  • Add return ducts

  • Seal leaky joints with mastic or foil tape

The DOE's Building America Solution Center has great visuals if you want to see what proper ductwork looks like.

Tip from Mike: Good airflow = good comfort. Ask your contractor for a “duct static pressure test” to make sure your system won’t be suffocating.


❄️ Step 5: Setting the AC Condenser and Line Set

Next up is setting the outdoor condenser unit—that big metal box that handles the cooling half of your system.

Here’s what happens:

  • The crew pours a new pad or levels the old one

  • They set the condenser on top, keeping it level

  • They install a new line set (the copper tubing that carries refrigerant)

  • They run low-voltage control wiring from the condenser to the furnace

With modern systems using R-32 refrigerant, your installer must follow updated safety and venting procedures. UL has issued specific standards for this, including UL 60335-2-40.


🔥 Step 6: Installing the Gas Furnace and Evaporator Coil

Back inside, the team will install the new furnace and evaporator coil, which work together to heat and cool your home.

What Gets Done:

  • Position the furnace (horizontal, upflow, or downflow)

  • Connect gas lines and check for leaks

  • Mount and connect the coil above or beside the furnace

  • Tie in the condensate drain

  • Hook up the flue venting system

  • Wire in the thermostat and safety controls

If your furnace is a 96%+ AFUE model, it will require PVC venting instead of metal flues. That might mean cutting new holes in walls or ceilings—completely normal.


🔧 Step 7: Pressure Testing and Refrigerant Charging

This is where experience counts. With everything connected, your installer will:

  • Pressure test the refrigerant lines with nitrogen to check for leaks

  • Pull a deep vacuum on the system to remove moisture and air

  • Charge the system with the correct amount of R-32 refrigerant

  • Start it up and monitor superheat and subcooling

Why does this matter? Too much or too little refrigerant can kill efficiency—and damage the compressor over time.


🎛️ Step 8: Testing, Balancing, and Commissioning

After charging, your tech will:

  • Run the system in cooling and heating modes

  • Confirm thermostat settings

  • Check delta T (the temperature difference between return and supply air)

  • Measure static pressure and airflow

  • Calibrate blower speeds and fan delay settings

They’ll also go over:

  • Filter access

  • Maintenance tips

  • What to watch for in the first few days

Tip from Mike: Ask for a commissioning sheet. It proves the system was set up right and is often required for rebates or extended warranties.


🧾 Step 9: Final Inspection and Cleanup

With the install done, the crew will:

  • Clean up all packaging, scrap metal, and debris

  • Schedule (or wait for) the city or county inspector

  • Walk you through basic operation and thermostat use

  • Register your warranty (or remind you to do it online)

Here’s where you take a deep breath and enjoy that first burst of quiet, even airflow.


⏳ How Long Does It Take?

Job Type Typical Time
Full replacement (same size/type) 1 day
New install with ductwork 2–3 days
Complicated upgrade or zoning 3–4 days

That assumes no weather delays, surprises in the attic, or structural repairs. Things like duct replacement or upgrading the electrical panel can add time.


💬 What You Should Ask the Installer

Here’s a short list of smart homeowner questions:

  1. “Did you do a Manual J or sizing calculation?”

  2. “Are the permits included?”

  3. “Is this a multi-stage or variable-speed system?”

  4. “Can I see the airflow and pressure test results?”

  5. “Who do I call if something isn’t working right?”

If your contractor seems annoyed by these, consider that a red flag.


✅ Final Thoughts: A Good Install = Long-Term Comfort

I’ll say it again: Your HVAC system is only as good as the install. You can drop big bucks on a fancy, high-SEER unit, but if it’s installed wrong—bad ductwork, poor charging, sloppy airflow—you’ll never see the benefits.

When you're ready to invest in a system that works as hard as you do, take a look at this full lineup of 3–5 ton R-32 AC and gas furnace systems from The Furnace Outlet. They’re built to perform—and built to last.


Need Help? Ask Mike.

Still have questions about your install? I’ve been in enough crawlspaces and garages to know the good, the bad, and the ugly. Reach out and I’ll help you steer clear of the junk and find a system you can count on—for winters, summers, and everything in between.

Cooling it with mike

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