I apologize if this happens to be repetitive, but these DIY turbulators were so easy and inexpensive that I had to pass it around. This should work for all boilers with vertical heat exchanger tubes. I have a Tarm Solo Plus 40. Has 8 hx tubes of 3" diameter and about 29" long. I had an old 1/2" link chain. I cut this into 8 29" lengths. I then took a 20d nail (about 1/4" diameter), inserted it through the top link, dropped the chain down a tube, using the nail to bridge the top of the tube and hold the chain in the middle of the tube. Repeat 8 times. Fire the boiler. Observe stack temp drop by 100F more or less. One website claims a 1% increase in boiler efficiency for each 40F drop in stack temp. Thus, 2-1/2% increase in efficiency. Cost to me: $0 -- all old, used items around the house. If anyone knows of a safety issue or danger in this setup, please advise. Happy New Year!