After you get so big. It has little effect.
But won't hurt.
Is he going to vane the return ell at the furnace. this will help a lot.
My duct pro said since I am going from 24x10 to 24x20 return drop....I won't need vanes.
Is he incorrect?
He also said that vanes provide benefits in rectangular ducts with abrupt changes in direction like 90 degree turns to "smooth" out the air in the direction you want it to go. He said for curved elbows the air is already being gently redirected and vanes won't buy you much more benefit.
The ell at the furnace has a lot of pd without them.
So a return ell at the furnace may have 65' or more of EL without vanes, making it equivalent to a smaller ell with vanes.
Ah, you didn't say he was using a radius ell the first time.
As an other example, WaterFurnace rated CFMs drop off after 0.5" ESP (through 4 tons) and 0.75" (5 & 6 ton).
Originally Posted by beenthere
Given how high key1's ESP is, and thus the reasonable guess that the variable-speed blower is going 'all out' trying to maintain 350/cfm but not achieving it, I believe key1's going to notice a good amount of operating cost reduction once he gets his ESP at 0.5" or less. My guess is key1 is currently not getting much, if any, of the cost savings benefit that variable-speed blowers are advertised with.
Ask your duct Pro to show you the equivalent lengths for the vaious typ elbows ,in Ma. D ,appendix 3.
The elbow shown in your pic.,entering the furnace return ,is 75', it could be 10'.
For a radius EL to be ,low loss,the inside radius must be half the wiidth of the duct,not a 90° with no inside radius,as shown in the pics.A square El is 80' and the one in the pic is 75'.
Think about how the air is flowing down the return drop,and the turn and turbulence that is happening ,without vanes or an inside and ouside radius El.
Heh they even put vanes in a double radiused EL ,to improve it.
Last edited by dash; 07-10-2008 at 01:14 PM.