If you're like many homeowners, you probably think that bigger HVAC systems are better. After all, it makes sense that a more powerful air conditioner would do a better job at keeping your home cool than a weaker system. Surprisingly, the situation is not nearly this simple. Instead, it's far more important to match your system's size as closely as possible to your home's unique cooling needs.
However, choosing the correct capacity for your home isn't just about maintaining a comfortable temperature. Instead, a correctly-sized system is also crucial for these three potentially surprising reasons.
1. Maintenance and Reliability
There are many things about air conditioning system design that may seem counterintuitive if you aren't familiar with HVAC equipment. For example, you might think that a large system won't have to work as hard to keep your home cool, reducing maintenance and increasing reliability. In reality, oversizing your air conditioner will likely result in more maintenance, lower reliability, and a shorter lifespan.
Air conditioning manufacturers design their systems to produce a particular temperature drop (known as "delta T") and to run in relatively short (but not too short) cycles. An oversized system will cool your home too quickly, resulting in short cycling as the system rapidly turns on and off. This behavior will inevitably cause more stress on system components, causing them to fail much more quickly.
2. Humidity Control
Humidity control is another area where sizing is crucial. Your air conditioner removes humidity from your home's air as a side effect. The evaporator coil transfers heat energy to your refrigerant, causing moisture to condense onto the coil's surface. This moisture drains into a condensate trap, removing it from your home and reducing humidity.
The key point is that the system can only remove moisture while running. An oversized system will invariably short cycle, cooling your home long before it can remove sufficient humidity from the air. As a result, the subjective comfort of your home is likely to be much worse than with a smaller system as a direct result of your oversized air conditioner reducing air temperatures too rapidly.
3. Temperature Comfort
You might think that, despite these other problems, it must be true that a larger system will still produce a cooler and more comfortable home. Unfortunately, oversized systems aren't even effective in this role. Since your system will reach your thermostat setpoint more quickly, you're more likely to experience wild temperature swings as the system repeatedly runs briefly and shuts off again.
Ultimately, a good option for any new air conditioner installation is to have a professional AC installation service perform a detailed load calculation. This calculation will tell you precisely what size air conditioner your home requires. Sticking to this recommendation will ensure your new system will keep your home cool while remaining as reliable and efficient as possible.