Air Conditioners and Heat Pumps. There’s a good chance you won’t ever think about the sound level of your air conditioner or heat pump … until, that is, you try to enjoy a quiet conversation with some friends in your back yard. Sometimes noise from condensing (outdoor) units even interferes with your peace and quiet indoors, so it’s a factor you should at least look at when you’re comparing different models.

The sound level of outdoor units is measured in bels (similar to decibels), on a scale from 0 (barely perceptible sound) to 13 (the threshold of pain). 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.

Furnaces. There isn’t a standard sound rating system for furnaces like the bel system for condensing units, 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. Comfortmaker’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.