Received brock turbulator, 9' long came in 2 pieces , it fits in the last pass hx tube before it leaves the appliance, the tube is 5" diameter. the turbulator basically is a 3" piece of flat stock that is bent in a zig-zag pattern touching the hx pipe at each bend, about every foot. I used 2 thermocouples, one at each end of the last pass hx tube approx 10 ft apart from each other with the turb inbetween, i recorded temps of each thermocouple at 100deg intervals based upon a thermocouple in the secondary burn chamber, i used 1600, 1700, 1800,1900deg temps as markers for the turb readings cause this is the realistic range the garn operates. then i subtracted the 4 differential temps at each reading, added them together and divided by 4 , thus equaling the average differential temp between the two thermocouples in the last pass from burn at 1600, to 1900deg, i hope charts will explain. no turb 4.5' turb 6.75' turb 9.turb 1600 413-344 425-324 409-288 414-286 1700 448-371 440-330 410-292 418-296 1800 458-378 454-336 427-299 437-301 1900 476-392 471-353 428-303 442-305 ave diff 77deg ave diff 111deg ave diff 123deg ave diff 130deg between 2 hx tube thermocouples the 4.5' turb drops the ave flue temp by 34deg over the no turbulator , the 6.75 by 45deg and the 9' by a 52deg ave under the stock no turbulator set up. these were all run at 60hz/3450rpm. All of the different lengths were able to allow the garn to reach temps of over 2100deg in the secondary burn chamber, so i guess the added back pressure was minimal, however with th 6.75 and the 9' the flue stack condensation was present for almost the whole burn, maybe more efficient but for now with 20/25% mc wood i will stick with the 4.5' turb. also the starting boiler temps were around 160deg. Next week i will try the same tests monitored with a combustion analyzer and see what gives. thats all i got for now, would welcome any comments.