I have used a 20" x 48" trough with 3/4" copper tube in a 1 1/2" glass tube.
The glass tube made a lot of difference reducing heat loss.

"Morris Dovey" wrote in message ...
SJC (in wR6Xg.8519$ji5.3676@trnddc04) said:

| That is a nice sized trough, it should produce good heat.

My compadre in this project took the first temperature measurements
this afternoon. The results weren't too bad - more photos added to the
same web page (link below).

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/StirlingProject.html