They are loader than a well installed forced air system, but not by much.

Using them for heat does not work as well as cooling.

Moving air makes you fell cooler, even when you are trying to heat.

The vents need to be placed so that no one sits under them.

There is a perception that these units are loud.

I've heard the statement...

You can't push a large volume of air through small ducts without getting velocity noise.

They don't realize that high velocity systems use only 1/2 the air flow of standard duct systems and they also use a special sound attenuating duct that acts as a muffler to further quiet the system.

Like ANY type of duct system, if they are not installed properly, they will be loud.

If the proper guidelines are followed, they are as quiet as a well designed conventional duct system.

Here is a link that might be useful: Excerpt from the high velocity air conditioning alternative

"There is a perception that these units are loud. "

I have installed many of them, and they are louder than a well designed conventional forced air system.

Luckily the noise is very 'white noise' and falls off within a few ft of the outlet.

the moise is not air volume related,m jst ar speed.

The last feew fet of the flex duct for each outlet are designed to reduce the noise.

If you screw up the design they are VERY noisy.

Just a gentle rush of air sound, mostly if you are right under the outlet (as in you can look up inside it).

If you put a bend in just before the outlet it is worse.