For as long as I can remember, the agreed epidemic with ductwork was always undersized return ducts.  Although we are far from perfect with duct sizing in New England, I have frequently seen great strides in fixing this issue - particularly with replacement systems.  Lets face it, you should just be properly designing the duct system on new installations.  Undersized ducts cause great restrictions in airlfow, raising static pressure and lowering the cubic feet per minute (CFM).  Or, with ECM motors, raising the amperage draw above full load.  More recently, I continue to find efforts with regards to sizing, but other rules of duct design being ignored.  I am going to concentrate on one particular rule that can have the same affect as undersized ducts:

  • On supply and return, when the trunk is wider than the plenum, a transition fitting must be used!

Fig.1  No Transition: Filter Box

   Lack of transitions create turbulence and restrictions in your duct system.  Even if the Return Duct is large enough for your desired CFM, abrupt changes in sizes without a tapered transition raises static pressure drastically above design.  Take Figure 1 for example.  Imagine the force needed to pull the same volume of air through the nice IAQ Filter installed.  At least the entire filter area is being used! I frequently find larger filter boxes than the air handler opening, a waste of filter area - but at least less of a restriction.

Fig. 2 Return Drop

  Figure 2 is an all too common mistake on replacement system, when installing a high performance filter in basement systems.  The new filter box pushes the return drop out of the range of connecting to the trunk, without an offset transition.  Most tin-knockers will do what they can to get the furnace operating.  Following this up by cutting in a grille in the return drop to either fix the undersized ducts, or lack of a transition, is not going to work when it comes to air-conditioning!  The air must come from the conditioned space in order to remove the latent heat, not from a moisture laden basement...

  Can anyone tell me what is going on in Figure 3???  I hope this wasn't you!

http://excessair.blogspot.com/2014/07/please-make-transition.html

Fig. 3 Supply Transition(s)?

Views: 85

Comment

You need to be a member of Home Energy Pros to add comments!

Join Home Energy Pros

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.

Latest Activity

Ethan Bukowiec replied to Ethan Bukowiec's discussion Thoughts on energy startup's new propane smart meter
"Anyone interested in learning more about this device should check out the Kickstarter…"
3 hours ago
Linda Wigington replied to Linda Wigington's discussion Low-cost electricity monitoring: Accuracy & Applications in the group 1000 Home Challenge
"Here is a response from Frank Bergamachi (Thousand Home Challenge project #4) I’ve looked…"
10 hours ago
Linda Wigington replied to Linda Wigington's discussion Low-cost electricity monitoring: Accuracy & Applications in the group 1000 Home Challenge
"Here is a response from Larry Kinney A few years ago someone had a gee whiz calibrated watt and…"
10 hours ago
Dale@EnergyWright replied to Linda Wigington's discussion Low-cost electricity monitoring: Accuracy & Applications in the group 1000 Home Challenge
"I've used the efergy Elite whole house energy monitor to evaluate 240V HPWHs. I found the…"
10 hours ago
Profile IconDale@EnergyWright and Maria Lacey joined David Eggleton's group
Thumbnail

1000 Home Challenge

Linda Wigington distinguished between deep retrofits & deep energy reductions, thus expanding…See More
11 hours ago
Profile IconAdam Swain, Cynthia Sandherr, James Skeldon and 2 more joined Home Energy Pros
11 hours ago
Tom White posted videos
19 hours ago
Maria Lacey replied to Linda Wigington's discussion Low-cost electricity monitoring: Accuracy & Applications in the group 1000 Home Challenge
"I attempted to use an AZTech device. I have used the Watt Stopper, Watts Up Pro, Kill-A-Watt…"
yesterday

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service