On the subject of HVAC returns...

[Jim Tiberio]

My home has about 900 sq feet per floor, 1st floor has a fairly open floor plan w/ four rooms and a half bath. 2nd floor has three bedrooms(each with a large walk-in closet) and two full baths. On the first floor fairly out of the way is one return, that is the only return on the floor. The second floor also has only one return and it is centrally located in the hallway. Will I get better and more even heating/cooling by leaving all doors open? One of the bedrooms is a guest bedroom so the door is always closed to keep the pups out. Also, the returns are both fairly loud, when we first moved in I actually thought there were fans running behind the vents. A friend of mine suggested the contractor didn't provide enough duct size to handle the quantity of air being moved. What would be the best solution to improve efficiency and reduce noise? It's that loud... Thanks!

[SQLit]

With out seeing the installation your bud could be right. What kind of filters are in the returns? Been changed lately? You then need to find the static air pressure of the fan in the air handler and then find a filter that is low enough to do a good job.

Try taking them out and then turn on the fan for a test. Still whistle, duct issue. Be sure you leave the return grill down for one test. Time to check the ductwork in the attic. Some one might have crushed a duct during a attic visit some time in the past.

[PipeDown]

Is the noisy-ness coming from inside the duct or from air rushing over the vent at the return opening. If the latter, a different vent cover might help.

Your friends suggestion must be based on the assumption the air is moving too quickly in the duct. That may not be true though it would be a source of noise. A perfect system would be quiet and be sized appropriately, your's may only satisfy the last part.

If your doors have at least some gap at the bottom, you should get good air mixing but if some rooms seal this gap due to carpeting, leaving the doors open will help. Excessively sealed rooms will be cool because the air can't get in, its already full.

Change your filters or if there is no filter, put one in. Running without a filter can cause the air to move too fast due to the fact the resistance from a filter is missing (especially newer high efficiency models). The filter also forms an acoustic buffer between the fan blades and the air intake register. High efficiency filters need to be changed more often (how ironic, what's efficient about spending more money and working harder ;-) )

[Nick Hull]

I have an open floor plan and put in NO return deliberately. The return air goes down the basement stairs, over a waist high door with the top always open. Very quiet and has worked well.