The HVAC Retrofit Playbook Every Property Owner Should Know By Now

You don’t need a new building to need a new HVAC system. In fact, most of the time I hear from people, it’s because their older system is on its last legs—or their energy bills just don’t make sense anymore. But ripping out old gear and installing something new isn’t as simple as swapping boxes. A retrofit is part science, part strategy. Get it right, and you’ll have clean, quiet comfort that runs for 15 years. Get it wrong, and you’ll be calling for service before the season’s even over. Here’s the playbook I’ve used for two decades to help property owners do it right.

Start With a Real Building Audit—Not Just a Guess

Before you order anything, you need to figure out what your building actually needs. That means more than knowing the square footage. A proper HVAC audit checks insulation levels, window types, ceiling heights, duct conditions, airflow, and local climate data.

A contractor or technician should use Manual J for load calculations and Manual D for duct design. If they’re not talking about those, they’re not doing it right. Don’t let anyone size your unit based only on the old one—it could have been oversized or undersized from day one.

I’ve seen homeowners buy a 5 ton air conditioning unit when a 3 ton AC would have done the job better and cost less to run. Know the real numbers before you sign a purchase order.

System Selection: One Size Does Not Fit All

Once the building’s needs are mapped, you’ve got to choose the system that matches. That doesn’t just mean the right size—it means the right type.

For rooftop applications or mobile homes, central heat and air package units offer a great all-in-one solution. They save space and simplify installation. But for most residential retrofits, split systems are the go-to.

This is where pairing matters. The condenser and the air handler need to be compatible, or the system won’t deliver its rated performance. You’ll also want to choose the right refrigerant type—most systems are transitioning away from R-410A, so buying something future-ready is a smart move.

Look at features that support long-term efficiency. Two-stage or variable-speed compressors. ECM blower motors. Coil coatings for corrosion resistance. UV light options like this one to help with air quality and system cleanliness.

And of course, register your warranty. If you’re using a Goodman system, make sure you complete the Goodman product registration immediately. It's free insurance for your investment.

Installation Planning: Lay Out Every Step First

With your system picked and ordered, the install needs to be mapped out. That means knowing where each piece goes, what tools are required, what clearances are needed, and whether electrical or structural work will be involved.

You’ll want to coordinate any electrical panel upgrades or thermostat rewiring. Make sure the breaker box has the right capacity if you’re switching from gas to electric heat. This is where involving an experienced HVAC installer pays off, even if you’re managing the project yourself.

Plan for staging and delivery too. If you’re bringing in a 5 ton air conditioning unit, you need equipment space and lifting support if it’s going on a roof. Don’t assume everything will show up at once—have a checklist of system components and verify deliveries as they arrive.

Design and Layout: Ducts, Lines, and Vents Matter

This is one of the most overlooked areas. I’ve seen too many installs where brand-new equipment was hamstrung by leaky, poorly sized ductwork. That kills efficiency and leaves rooms unevenly conditioned.

During your retrofit, inspect all duct runs. Replace sections with visible damage or signs of rust. Reseal joints and replace old insulation as needed. And above all, make sure your return and supply sizes match the airflow of the new unit.

Line sets matter too. If you’re upgrading refrigerant types, you might need to change the copper lines. Some systems can be flushed and reused, but only if they meet the specs. Your contractor should verify this before installation day.

Vent placement also affects performance. You want balanced air delivery, not one room that’s freezing and another that never cools. Make adjustments before everything is sealed up again.

Commissioning and Startup: Not Optional

When the system’s installed, it has to be commissioned properly. This means setting airflow rates, adjusting blower speeds, verifying refrigerant charge, calibrating the thermostat, and confirming that every part runs as expected.

This isn’t just plug-and-play. It’s what separates a great install from one that runs poorly. Make sure your contractor tests the static pressure and airflow at startup. That will tell you immediately if the ducts and blower are aligned.

Once everything’s tested and working, write down the startup data. Keep it with your system records, along with your warranty, manual, and any install permits. This makes service easier and protects your investment.

Maintenance Best Practices Going Forward

After install, the work isn’t done. To keep that new system running right, you need a maintenance routine.

Check and replace filters regularly—especially if you’re using enhanced filtration or have pets. Keep outdoor coils clean and clear of debris. Check drain lines for blockages and make sure condensate pumps are working.

If your system includes zoning, dampers should be inspected and tested. If you’ve added air purification like a UV light, the bulb should be replaced annually.

Schedule a professional service once a year to check refrigerant levels, electrical connections, and overall system performance. You spent the money—protect it with regular care.

Frequently Asked Questions

How long does an HVAC retrofit usually take?

Most residential retrofits take 1 to 3 days, depending on ductwork, electrical changes, and equipment access. Commercial installs may take longer due to staging and permits.

Can I reuse my existing ductwork?

Only if it’s in good condition and properly sized. Leaky or undersized ducts can ruin performance. An airflow test can tell you if it’s worth keeping.

What’s the biggest mistake in HVAC retrofits?

Oversizing the equipment based on the old system. Always do a fresh load calculation. Bigger isn’t better—proper sizing is the key to comfort and efficiency.

Is a matched system really that important?

Yes. Mixing brands or models that aren’t certified to work together can cause efficiency loss, control issues, and warranty problems.

Do I need a permit for an HVAC retrofit?

In most areas, yes. Permits ensure the install meets code, especially for electrical work and refrigerant handling. Your contractor should pull them for you.

Final Thoughts from Mike

A good HVAC retrofit isn’t about guessing or getting lucky. It’s about knowing your space, picking the right system, and following the install all the way from planning to commissioning.

Most of the problems I’ve seen over the years could have been avoided with a little more prep and a little less rushing. That’s why I always tell people—don’t wait for your system to fail. Plan ahead, get your equipment now, and do it the right way the first time.

Whether you’re replacing a rooftop unit, switching from gas to electric, or just want a quieter, cleaner system—this guide is the place to start. And if you need help picking the right unit, that’s what we do every day.