Do I Need a Bigger AC Unit for My Home Addition?

Adding square footage to your home—whether it’s a new bedroom, sunroom, bonus space, or an expanded kitchen—is an exciting project. But with more living space comes more demand on your HVAC system. One of the most common questions we hear from Cleveland-area homeowners is: “Do I need a bigger AC unit for my home addition?”

The answer isn’t always straightforward. In this post, we’ll break down the key factors to consider when evaluating your current air conditioning system and how to make the right choice to keep your whole home cool and comfortable.

Will Your Current AC System Handle Your Home Addition?

When you add new square footage to your home—whether it’s a bedroom, sunroom, in-law suite, or finished basement—it’s easy to focus on the layout, design, and finishes. But one thing many Cleveland homeowners overlook is whether their existing HVAC system can handle the additional space.

Your air conditioner was originally sized based on your home’s square footage, layout, insulation, and energy demands at the time it was installed. A home addition increases your overall cooling load, and pushing your current system beyond its limits can lead to performance issues, higher energy bills, and long-term equipment wear.

Here’s how a home addition can impact your existing AC system—and the signs to watch for if it’s not keeping up.

Why Additions Stress Your Current HVAC System

Expanding your home changes several variables that directly affect how your air conditioner performs:

• • Increased Cooling Load
    More square footage means your AC has to condition a greater volume of air. If the system wasn’t designed to handle the added space, it may run longer and harder without delivering consistent results.
  • Additional Windows and Exterior Walls
    Many additions include large windows, sliding doors, or exposed walls—especially in sunrooms and upstairs bedrooms. These surfaces often let in more heat, especially if they’re not well insulated or shaded, which increases the demand on your cooling system.
  • Air Distribution Challenges
    Extending existing ductwork into a new space isn’t always ideal. If not balanced correctly, it can reduce airflow to other parts of the home, creating hot and cold spots throughout.
  • Comfort Disruptions
    Even if your current AC “seems” to be working, you might experience reduced airflow, uneven temperatures, or long run times. Over time, this strain can shorten the life of your system or lead to frequent repairs.

Warning Signs Your AC Might Be Undersized

Not sure whether your system is struggling to keep up? Here are common indicators that your AC may no longer be properly sized for your updated home:

• • Uneven Temperatures
    You feel warmer in the new addition or other rooms that were previously comfortable. This usually signals an unbalanced system or inadequate cooling capacity.
  • Longer Cooling Cycles
    Your AC runs for long periods but still doesn’t cool the home effectively. This could mean the unit is undersized for the new space.
  • Short Cycling
    The system turns on and off frequently, indicating it’s either struggling to regulate temperature or improperly sized for the demand.
  • Higher Energy Bills
    If your cooling costs have spiked since completing your addition, your AC may be working harder than necessary, consuming more electricity in the process.
  • Weak Airflow from Vents
    If new or existing vents produce minimal airflow, your system may be stretched too thin or your ductwork may not be properly balanced.

If you’ve noticed any of these issues since finishing your home addition—or you’re planning one—it’s worth having your system evaluated before peak summer temperatures arrive. At Hardin Bros HVAC Services, we can assess your home’s updated cooling needs and recommend the best solution to ensure even, efficient comfort throughout your space.

What Are My Options for Cooling a Home Addition?

Every home addition is unique—whether it’s a ground-floor bedroom, second-story extension, or enclosed sunroom. The right cooling solution depends on your existing HVAC system, the layout of your home, and how the new space will be used.

Here are the three most common and effective strategies for keeping your Cleveland-area home addition cool and comfortable:

1. Upgrade to a Larger Central AC Unit

If your current air conditioner was already running near capacity before the addition, upgrading to a larger unit may be the most efficient and long-term solution.

Benefits of upgrading your AC system:

• • • Even cooling throughout the entire home – A properly sized system delivers consistent comfort to both old and new areas without compromising airflow.
    • Improved energy efficiency – Your new AC unit will not only be larger, but also more efficient than older models, helping to reduce utility bills over time.
    • Better performance in extreme weather – Northeast Ohio summers can be hot and humid. A new unit built for the full square footage of your home ensures reliable performance during peak demand.
    • Ideal for seamless home integration – Perfect for additions that are fully tied into the main floorplan and require central temperature control.

At Hardin Bros HVAC Services, we perform detailed load calculations to make sure your new system is sized specifically for your home’s total square footage, insulation levels, and layout.

2. Add a Ductless Mini-Split System

For many Cleveland homeowners, a ductless mini-split is the most practical solution for cooling a home addition—especially when the space functions independently from the rest of the home.

Advantages of ductless mini-split systems:

• • • Zoned temperature control – Set a different temperature in your addition without affecting the rest of the home. Ideal for guest rooms, home offices, sunrooms, or in-law suites.
    • No ductwork required – These systems eliminate the need to extend your central HVAC ducts, which can be expensive, invasive, or impractical.
    • High efficiency and quiet operation – Mini-splits are among the most energy-efficient cooling options on the market today, and they operate almost silently.
    • Fast, clean installation – We can usually install a mini-split in one day with minimal disruption to your home.

We install ductless systems throughout the Cleveland metro area, especially in cases where the existing system is still in good shape and doesn’t need a full upgrade.

3. Extend Existing Ductwork (With Caution)

Extending your current duct system into the new space may seem like the easiest option, but it’s not always ideal—especially if your AC system wasn’t designed for the added load.

This option may work if:

• • • Your current AC system has enough unused capacity to handle the cooling needs of the new addition.
    • Duct sizing and layout are adjusted to ensure balanced airflow throughout the home.
    • You’re willing to invest in rebalancing or zoning modifications to maintain comfort in all rooms.

Potential drawbacks:
Extending ducts improperly can lead to reduced airflow in existing rooms, uneven cooling, and an overworked system that breaks down sooner than expected.

That’s why at Hardin Bros HVAC Services, we perform a full evaluation of your HVAC system and ductwork before recommending this approach. If extending the ducts isn’t the best choice, we’ll give you honest guidance on more efficient alternatives.

Why Proper Sizing Is Critical

When it comes to air conditioning—especially in homes with additions—bigger is not always better, and smaller definitely isn’t either. An improperly sized HVAC system can lead to a long list of problems that affect not just comfort, but also energy costs and system longevity.

An undersized system will struggle to keep up with demand. It may run non-stop without ever reaching the set temperature, leading to excessive wear, higher utility bills, and insufficient cooling—especially during Northeast Ohio’s hottest months.

An oversized system, on the other hand, cools the space too quickly and shuts off before completing a full cooling cycle. This may sound like a good thing, but in reality, it prevents proper dehumidification, leaving your home feeling clammy or “sticky.” It also causes the system to short cycle, which leads to uneven temperatures, more frequent breakdowns, and a shorter equipment lifespan.

That’s why proper sizing is absolutely essential—particularly when your home’s layout or square footage changes due to a new addition.

At Hardin Bros HVAC Services, we never guess. We perform accurate manual load calculations to determine exactly what your home needs. This method goes far beyond basic square footage and considers critical factors such as:

• • Total living space and ceiling height
  • Insulation type and R-values
  • Window placement, size, and orientation
  • How many people live in the home and how often it’s occupied
  • Heat-generating appliances and lighting
  • Sun exposure and shading from trees or neighboring buildings

By evaluating your home as a whole—not just the new addition—we ensure your system is properly sized for both immediate performance and long-term energy efficiency. This results in better comfort, lower operating costs, and fewer repairs down the road.

Proudly Serving the Greater Cleveland Metro Area

Hardin Bros HVAC Services provides expert AC repair, system upgrades, and ductless mini-split installations throughout:

• • Cleveland
  • Rocky River
  • Fairview Park
  • Lakewood
  • North Olmsted
  • Parma
  • Parma Heights
  • Middleburg Heights

Whether you're planning a home addition or dealing with uneven cooling in a newly expanded space, our team is here to help you stay comfortable and efficient year-round.

Planning an Addition? Let’s Make Sure Your AC Can Handle It

Don’t let your home addition create cooling problems.

If you’re building a new space or have already completed an addition, reach out to Hardin Bros HVAC Services. We’ll evaluate your current air conditioning system, perform a proper load calculation, and recommend the most efficient and cost-effective way to keep your entire home cool.

Call today or request a free estimate—we proudly serve homeowners across the Cleveland metro area with trusted HVAC solutions tailored to your home.