One factor of comfort most people don't consider is sound. How can you relax when you have a noisy system? This section provides tips on how to make sure you are getting the quietest system available.
 

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. Sound levels inside your home may also be reduced by matching your outdoor unit with a variable- capacity furnace or fan coil.

There isn’t a standard sound rating system for furnaces, so it’s difficult to compare models.

However, models that have two-speed or variable-speed operation typically also offer lower operating sound levels, because there is less noise from the blower motor and from air turbulence at lower speeds. Carrier’s variable- capacity models even have a "ramp-up" feature that gradually introduces warm air into your ducts, helping prevent the "creaking" noises that come from ducts expanding and contracting.

Since two-speed and variable- capacity models normally run on "low" speed up to 90% of the time, you’ll find they’re a sound solution when you want to enjoy peace and quiet.

Decibels are normally measured 4 feet from the sound producing device. All legitimate air conditioning manufacturers will provide you with decibel sound power levels of their condensing units and heat pumps. Sound power level ratings for furnaces are more difficult to find.

Click on the 64dB level and then turn up the volume on your computer until you can just barely hear it. It should be about the same sound level that is produced by the cooling fan on your computer. With your sound at this level for the 64dB rating, when you click the other dB ratings they should be very close to what you would hear from the actual unit.

For even more accurate results you can purchase a sound level meter (available from Radio Shack for around $35.00). Hold the sound meter approximately 2 inches away from the speaker on your computer, use the C weighing scale and you can actually read the sound power levels, therefore determining approximately how your condensing unit or furnace will sound. Just vary the volume control on your computer until the sound level meter reads the decibels that the manufacturer has given you for that unit.