How do I rate an air conditioner for sound?

An air conditioner or heat pump sitting next to your house can create a lot of noise both inside and outside your home. To compare sound levels of different brands, ask your dealer about the bel rating of units you are considering. Bels, similar to decibels, range from 0 to 13. Most air conditioners and heat pumps operate at 8 to 9 bels; some units’ ratings are as low as 6.8. That may not sound like a wide range, but consider this: 9 bels sounds 10 times louder than 8 bels. That means one 9-bel air conditioner is as loud as 10 units rated at 8 bels. So we think taking the time to compare bel ratings is pretty sound advice. Matching your outdoor unit with a variable-capacity furnace or fan coil may also reduce sound levels inside your home.