Heat and cold air return for Solar Panel

Well it seams you solar collector was installed wrong to began with. When air is heated it expands so the supply air should be the 8" duct.

As to duct sizing? Sorry no help here as there's just too many design considerations, like grains of moisture per pound of air, fan CFM at what static presssure, and the big one, hot air will rise and cold air sinks.

Since your collector is located higher than your treated rooms, this creates considerable engineering thoughts for correct design, as in many books on the subject.

Sorry but I just don't have the time to engineer such system.

The best idea would be to do some serious reading then make your best trial and error install. It will work but at somewhat less efficency than a well designed engineered system.

T_Bone

3 X 10 is a convenient size because it can be completely contained in a 16" OC 2x4 stud channel, which I believe is still the most common framing for interior house walls. If the walls aren't open, or the installation doesn't allow for opening them, 3 X 10 still protrudes into the room only 1/2 as much as 6" round. By volume 3 X 10 provides about 6% more air than 6" round, but only 60% of what 8" round provides.

T_Bone is the person who can answer the question about the need for insulation.

Stretching your project over several years sounds depressingly familiar. I've come to the conclusion that the reason I do it is because, as an existentialist, it gives me something to live for. That sounds better than "lack of focus" doesn't it? Maybe not.

All the best, Stan

I may know of a place in your area where you can get a round tuit---but you'll have to hurry. You can't wait if you ever want to get a round tuit. That's not an oxymoron, so it must be a conundrum.

Roy is indeed east of Lacey, but the southern half of the Fort Lewis Military Reservation is between them. Here in west Olympia we hear a lot of what sounds like thunder from Fort Lewis. In Roy it must shake the dishes out of the kitchen cupboards, but I suppose that people in Roy view it as a fair price to pay for the privilege of living in the middle of nowhere.

Fort Lewis always posts a phone number in the Olympia newspaper for people to call to complain about the artillery noise. I think it's a nice gesture. You call, you complain, nothing changes---your government inaction.

All the best, Stan