Undersized AC Unit

What Happens if My AC Unit is Undersized
Most Frequent Signs of an Undersized AC Unit

1. Inability to Maintain Temperature: Your AC unit may struggle to maintain the desired temperature on hot days. If your home remains warmer than your thermostat setting, even when the AC is running constantly, this is a sign of an undersized unit.
2. Long Run Times: An undersized AC unit may run for extended periods, leading to higher energy bills and increased wear and tear on the system.
3. Uneven Cooling: You might notice that some rooms or areas in your home remain much warmer than others, indicating that the AC is not adequately cooling the entire space.
4. Constant Cycling: An undersized unit may cycle on and off frequently, which can reduce its lifespan and efficiency.

What to Do about an Undersized AC Unit

(Sorted by Least Expensive to Most Expensive)

1. Use Fans and Curtains
   • Ceiling fans and heavy curtains can help distribute cool air more effectively and block out heat from the sun. Using existing ceiling fans and curtains is a very low-cost solution. If you need to purchase ceiling fans, they can range from $50 to a few hundred dollars each. Curtains vary in price depending on quality and quantity.
2. Seal Air Leaks
   • Seal any gaps, cracks, or leaks in your home’s windows, doors, and ductwork to prevent warm air from infiltrating and cool air from escaping. Sealing air leaks typically involves purchasing caulk, weatherstripping, or insulation materials, which can be relatively inexpensive, usually ranging from $20 to $200, depending on the extent of the work.
3. Regular Maintenance
   • Ensure that your AC unit is well-maintained with regular cleaning and professional inspections. This can help improve its efficiency and cooling performance. Routine AC maintenance costs can vary, but a standard annual service check may range from $100 to $200. The cost of maintenance is relatively low compared to other solutions.
4. Improve Insulation
   • In some cases, improving the insulation in your home can help alleviate the problem of an undersized AC unit. Proper insulation helps retain cool air and reduce the load on the AC. The cost of improving insulation can vary widely depending on the scope of work and the size of your home. DIY insulation projects can start at a few hundred dollars, while professional insulation installation for an entire house can range from a few thousand to several thousand dollars.
5. Thermostat Adjustment or Replacement
   • Adjusting or recalibrating an existing thermostat is low cost (typically free if done by the homeowner). Replacing a basic thermostat with a programmable one can range from $50 to $200, while more advanced smart thermostats can cost $200 to $300 or more.
6. Proper Sizing and Installation (If Needed)
   • If your AC unit is indeed undersized, you may need to consider upgrading to a larger, appropriately sized unit. A professional can help you select the right size and model for your home. The costs can vary widely based on factors like the size and efficiency of the new unit, installation labor, and any necessary ductwork modifications. This can range from a few thousand dollars to several thousand dollars.
7. Zoning System Installation
   • Consider installing a zoning system, which allows you to control the temperature in different areas of your home independently. This can help compensate for an undersized unit by directing more cooling to areas that need it most. Installing a zoned system can involve additional equipment and labor costs. This solution typically ranges from a few thousand dollars to several thousand dollars, depending on the complexity of the installation and the number of zones you need.

The extent of the work required and regional labor and material costs will affect the ultimate cost to solve the problem. If you believe you have an undersized AC unit, consult with a professional HVAC technician for a qualified assessment of your specific needs and costs.