If you've ever woken up in the middle of the night from an obnoxiously loud furnace, you can understand the frustration carried with it. So much so that you will ask about noise level when you start looking for a new one. It may not be on the priority list for all, but there are certain things you should ask about when considering noise-levels of your HVAC system.
The Air Conditioning, Heating, and Refrigeration Institute (AHRI) has established standard ratings for equipment noise. Having a standard rating helps measure noise levels so you don't have a system installed that sounds like a gang of raccoons in the vents. Sound Rating Numbers (SRN) are based on bels. One bel equals ten decibels and the higher the number, the louder the unit. A standard A/C unit is rated between 7 and 9 bels. It may seem like a minor difference, but remember that each bel is ten decibels, so a rating of 9 is actually ten decibels louder than an 8.
Make sure to ask for the rating of your current system and options you have for a new furnace. If you don't know how loud it's going to be, you might wind up with a noisier one.