How to Retrofit Central AC Into an Older Home Without Ducts

Living in an older home has its perks, charming architecture, solid craftsmanship, and plenty of character. But it often lacks one key modern convenience: central air conditioning. If you’re sweating through the summer and dreaming of cool, consistent indoor temperatures, you’ve probably asked yourself the question: Can I retrofit central AC into my older home without any existing ductwork?

The short answer: Yes, you can. The better news? You can do much of the planning, prep, and even parts of the install yourself, no need to rip open walls or gut your historic beauty. With the right approach, retrofitting AC into a ductless home is not only possible, it can be surprisingly smooth.

This guide walks you through the process, options, tools, and steps to take if you want to take on this home upgrade.

Your Options for Duct-Free AC Retrofits

Older homes typically weren’t built with air ducts in mind, but that doesn’t mean you’re stuck with window units forever. Here are your top retrofit options:

Option 1: High-Velocity Mini-Duct Systems

These use narrow, flexible tubing (usually 2-inch diameter) that can be snaked through walls, ceilings, and floors with minimal disruption.

• Pros: Discreet, works well with older architecture, less invasive than traditional ducting.
• Cons: More expensive upfront, requires a specialized air handler.

Option 2: Ductless Mini-Split Systems

These are extremely popular for retrofits. Each indoor air handler connects to an outdoor compressor via small refrigerant lines.

• Pros: No ducts needed, efficient, zoned cooling.
• Cons: Indoor units are visible, might need multiple for larger homes.

Option 3: Traditional Ductwork (with Creativity)

If you’re set on standard central AC and don’t mind some remodeling, you can install full-size ductwork creatively, through closets, soffits, attic spaces, or even basement chases.

• Pros: Full-home AC from a central system.
• Cons: More invasive, requires construction, best paired with renovation projects.

Prep,  Measure, and Map Your Cooling Needs

Before picking up tools or parts, you need a plan.

Perform a Load Calculation

This determines how much cooling your home needs, typically measured in BTUs (British Thermal Units). You can use online tools or consult a manual J calculator to figure it out based on:

• Square footage
• Ceiling height
• Insulation levels
• Window placement
• Sun exposure

Tip: Oversizing your AC can be just as bad as undersizing, more humidity, short cycling, and higher energy bills.

Identify System Layout

If you’re going mini-split:

• Decide which rooms need wall units. Bedrooms? Living room? Kitchen?
• Determine where to run refrigerant lines, usually through exterior walls.

If you’re going high-velocity:

• Map locations for outlets (usually in ceilings or high on walls).
• Plan the main trunk line route through an attic, crawlspace, or basement.

Choose the Right System and Sizing

Now that you have a rough load calculation, it’s time to pick your system.

• Mini-splits: Units range from 9,000 to 24,000 BTUs. A 3-head system can cool a small home efficiently.
• High-velocity systems: Centralized unit connects to multiple small ducts, great if you want central control.
• Traditional ducted systems: Opt for a 2- to 3-ton unit for an average 1,500–2,000 sq ft home (consult sizing charts).

Tip: Purchase equipment with SEER ratings of 16 or higher for better efficiency and rebates.

Install the Indoor Units or Ducts 

If You Choose Mini-Split:

1. Mount the indoor head unit on an exterior wall. Use the included bracket and level it properly.
2. Drill a 2-3 inch hole through the wall to route the lines.
3. Insert the refrigerant lines, condensate drain, and power cable.
4. Caulk around the hole to seal it from weather.
5. Do this for each head unit.

Note: Line charging and final hookup should be done by a licensed HVAC tech, as handling refrigerant requires EPA certification.

If You Choose High-Velocity:

This takes more skill and planning but is manageable for experienced homeowners.

1. Install the air handler in the attic or basement (must be level and secure).
2. Run main trunk lines through accessible cavities, attic rafters or crawlspaces work well.
3. Cut small holes in ceilings for outlet vents.
4. Connect mini duct tubes from the trunk to the outlet points.
5. Seal and insulate everything to reduce noise and boost efficiency.

Connect to the Outdoor Unit

Whether you’re using mini-splits or central air, you’ll need an outdoor condenser.

1. Set a level pad for the unit on a flat surface (concrete or prefab AC pad).
2. Mount the line set bracket on the wall and run refrigerant lines through it.
3. Route drain line and low-voltage control wire to match unit specs.
4. Leave final refrigerant charge and power connections to a pro unless you’re certified.

Tip: Use line set covers for a clean finish on the exterior of your home.

Install Thermostat and Electrical

Most systems work with smart thermostats, or you can install a basic one.

1. Mount the thermostat base on the wall and pull wires through.
2. Connect the wires based on your system (mini-splits often use remotes, others need full connections).
3. Secure the faceplate and test operation after powering the system.

As for electrical work, you’ll likely need:

• A dedicated 240V circuit for the outdoor unit.
• A disconnect box mounted near the condenser.
• Wiring run through conduit.

 If you’re not familiar with electrical wiring, hire a licensed electrician for this portion.

Insulate and Seal

No matter what system you install, sealing is crucial for performance:

• Wrap all ducts or refrigerant lines with insulation.
• Seal wall penetrations with spray foam or caulk.
• Use weatherproof tape or covers for outdoor terminations.
• Insulate attic or crawlspaces near equipment for added efficiency.

Test and Optimize

Once everything’s in place and connected:

1. Power up the system.
2. Test each room for consistent airflow and cooling.
3. Check for leaks or condensation.
4. Program thermostat settings or remote timers.
5. Make sure outdoor compressor runs quietly and shuts off properly.

Your system should cool quickly, with quiet operation and no rattling or dripping indoors.

Final Thoughts: A Cool Upgrade, Done Right

Retrofitting central AC into an older home might sound intimidating, but it’s entirely possible. Whether you choose a ductless mini-split system, a high-velocity mini-duct setup, or go all-in with full-sized ducts, you can modernize your comfort without tearing your house apart.

Here’s what to keep in mind:

• Do your research and plan layout carefully.
• Get help for the parts that require licensing (like refrigerant charging or heavy-duty wiring).
• Take your time, seal thoroughly, and insulate well.

The result? A cool, comfortable home, even in the hottest months, without sacrificing the charm of your older space.

Where To Find Us 

If you need any replacement parts for your appliances, you can enter your model number at AppliancePartsPros.com to locate and order them quickly. Most orders arrive in just two business days, and we have tons of great information in our repair help section and YouTube videos to help you troubleshoot.

Stay connected with the latest DIY tips, tutorial videos, and repair guides by following us on Facebook, Instagram, and Twitter. We love hearing about your repair stories and successes. If you need more help or want personalized guidance, feel free to reach out. We’re ready to help you take on your next project with confidence!

The information in this article may not apply to your specific appliance model. We recommend consulting your manufacturer’s documentation or contact us with any questions.