Dead-Ends in the crawlspace ductwork. Should they be removed? Or do they help?


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Old 09-24-11, 06:29 AM
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Dead-Ends in the crawlspace ductwork. Should they be removed? Or do they help?

I noticed extra duct at the end of both runs of ductwork. I asked a handyman if that may cause the airflow to bounce back thus slowing down the airflow. And that maybe I should remove that excess area from the system. This is a square type duct.
He says that it actually helps the air movement by having it.
This doesn't make sense to me.
Could someone please verify whether it harms or helps the airflow in my ducting system for my heating/A/C? And if you don't mind explaining how, I'd appreciate it very much.

Here is a drawing of what this looks like with the dead ends.



P.S. The blockage marked is some clothing that the previous owner stuffed in the duct. I guess he was hoping it would improve air pressure. I am thinking of cutting that line out in hopes that it will improve.

Thank you in advance.
 
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Old 09-24-11, 07:33 PM
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Branch lines should never come off the end of the main line. Two feet to 3 feet is best
 
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Old 09-25-11, 05:03 AM
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Ok, so this is fine then. It's actually better this way. That's amazing. Any links/info as to why this works this way?

Also, should I have that branch with the blockage removed or can I leave it as is? This is a dead end branch, but will it make any difference. Just wondering cause it would save an effort if it didn't matter that that blocked branch was there. Who knows, maybe I'll need to open it up at a later time. Haven't lived in the place a year yet. Still trying to figure out how to improve the airflow in the system. It's terribly weak...

Thanks for the reply.
 
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Old 09-25-11, 07:26 AM
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Leave the duct like it is. It works off of pressure the main duct has to pressurrise before sending air to the rooms if you remove it the branch lines at the end will have more air than the rest of the system. I'm guessing you don't have dampers because they blocked off the duct. Dampers would be best but if it works then I guess it's fine
 
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Old 10-22-11, 11:12 PM
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Didn't know you replied to this thread. I must have missed the email notification for replies.
Thanks for the explanation and suggestion. I am going to consider adding a damper to a couple of locations.

Thanks!
 
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Old 10-23-11, 06:31 AM
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Hi foolios,
Just to add, opening and closing supply vents can be problematic. The total air flow is initially set to handle the total heat being produced by the burner. Reduce the air flow and the plenum temperature will increase. Increase the air flow and the temp will go down. There is some margin in this process, but at the extremes. ie too little air, the plenum will heat to the high limit setting and the burner will cycle off while the plenum cools down. This is a safety feature and not something that should be happening on a regular basis. On the other end, with too much air the plenum will cool below the lower setting and here the blower will cycle off while the burner continues to bring the plenum up to operating conditions. Short cycling on the high limit reduces efficiency and short cycling on the lower limit reduces comfort.

Airman covered the trunk line extensions, but to add, if you were to add a smooth sweep 90 supply line right at the end, the air would flow very easily around the corner and to its destination. With the dead end it creates a trunk pressure so that all branches are fed by similar pressures. Yes it creates some turbulence, but that is the desired intention. However, know what is happening and why gives those of us who might want to increase the flow to the very another option. Ducts that branch at 90 vs ducts that branch at 45 also create different air flows.

For the record, I'm far from a HVAC pro, but with my own air handler I had to pull the squirrel cage and clean each fin. Simple vacuuming was only removing the lint and surface dirt, but the crusted accumulation was seriously reducing my air flow.

Best
Bud
 
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Old 10-24-11, 09:16 PM
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Thanks for the extra info. Amazing how much there is to consider.
 
 

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