To be honest, I'm not sure my 'air flow thingy' :lol: is what I was hoping for, It is used to read wind speed outside. With the springs in place I get about 5 mph and without them, I get about 3 mph. So the springs have definitely restricted the flow somewhat causing a higher speed OR the spiraling of the air is causing strange things to happen to the readings. I haven't really had time to compare areas with and without the springs to see if I can draw any conclusions such as 'are the springs really restricting total cfm?' Have to also look at btu's coming out too but I'm not ready for that one!