[solarhotairpanels]

Xringer

In ref to fan noise....
I run 6 inch duct fans in my solar heated hot air collectors
My fans are outside but are piped in thru the side of my house and run along under the floor joists about 4 to 5 ft to the registers.

When first installed I ran 6 inch metal tubing insulated on the outside all the way to where the registers were located. When the fans kicked in the registers sounded like a tornado, just nuts so I tried something different.

I removed about 4 to 5ft of metal tubing from the register back toward the collectors and installed flexible 6 inch insulated duct hose in it's place... man what a difference.

99% of the noise went away

Is there a way you could move your fan back into your attic and install the insulated duct hose leading to your register? It may help big time.

Something else I would do is change over to 8 inch fan and ductwork.
Just my opinion.

I don't think the little 4 inch fan is capable of moving enough volume to your basement to accomplish your mission.

Just some thoughts.. I'm not an expert but a larger fan would most likely work less and move a heck of a lot more air.

...at my house:
I recently installed a new Navian Combi hot water Boiler in the laundry room here at our house. The new unit required 1 1/4 inch copper pipe manifold below the boiler and a whole bunch more additional copper piping around the boiler which is radiating tons of heat so our small laundry is now heating up in there pretty good much warmer then the rest of the house.

My plan is to do what you are doing and pump that warm air down to our basement.
I'm going to use an 8 inch fan and controller so it turns on/ off on it's own once installed.
I would love to use a 12v powered fan powered by a single panel solar panel but not sure I have the patience to put all that together. :-)
I have a pool table down there and would really love to be able to shoot pool without having to wear gloves. :-)