Impeded Air Return an Issue?


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Old 06-08-13, 06:49 PM
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Impeded Air Return an Issue?

I just replaced my old 3 ton unit with a proper sized 2.5 ton 14 seer xl14c Trane. A contractor replaced the unit, repaired and replaced duct work. Should I be worried about impeded air flow due to the following preexisting scenario:

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Old 06-08-13, 07:12 PM
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Call him back and have him fix that.
Reduced return air floor can cause the unit to freeze up, and reduce the amount of output.
 
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Old 06-09-13, 06:59 AM
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The mouth of the duct should always be centered in respect to the filter, & the return filter box needs to be 'deep enough' so there is no funneling of Return-Air largely through the area of the smaller duct's mouth opening, - being way too close to the filter.
 
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Old 06-09-13, 07:06 AM
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Unless he specifically did that and it was not preexisting then you will likely have to pay for the added work.
 
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Old 06-09-13, 02:39 PM
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how would that issue be remedied since the joist and frame areblocking?
 
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Old 06-09-13, 04:35 PM
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Adding another return air and tying it into the return air plenum at your furnace would help airflow if this was the only return air.

A manometer reading of the external static pressure across your furnace and the furnace manual will tell you if you are moving 1000 cfm of air (400 cfm per ton).

350 cfm per ton could also be acceptable a many cases.

I doubt that you are getting even 350 cfm per ton at this time if this is the only return air duct to your furnace.
 
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Old 06-09-13, 04:42 PM
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jbrackett posted this on my behalf since I was out of town and wanted to get some feedback. I spent an arm and a leg to get a new trane unit installed and I was under the impression that he would fix any major problems with the duct system. Now I'm not an hvac technician, but I think of that photo as a crimp in a garden hose, I'm not going to get an even water flow. My house is small at around 1000sq ft and I honestly don't even know where returns would be placed in this little house. As far as fixing the current return, do I have any options? The HVAC company said that the return was "not a problem' and to just leave it, and I didn't have this specifically written into the quote.
 
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Old 06-09-13, 04:46 PM
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Ask if a static pressure test was performed to prove the system is flowing the proper amount of air for proper operation. Most companies don't check the static pressure unfortunately.
 
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Old 06-09-13, 04:59 PM
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is asking for a static pressure test asking too much? will I likely get an excuse? will it cost me more? will he lie and say he did it? will he tell me 500cm per ton rule or something?
 
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Old 06-09-13, 05:25 PM
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Well, it should have been done with the new install.... as far as asking too much.... I can't say because I know nothing about your contractor. As to the rest of your questions I refer you to "I know nothing about your contractor".
 
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Old 06-13-13, 01:00 PM
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That 16X25 pleated filter will only flow around 560-CFM at 300-fpm velocity through it, a higher velocity results in too high a pressure drop.

Therefore, 'two' 16X 25 filters would flow the 1000-CFM at a beginning 300-fpm velocity.
That would require not using one in the furnace; but using two in the conditioned areas; & in this case the other one could even be larger than 16X25.

ACCA Manual D requires 300-fpm velocity through a new clean cheap throwaway filter.
 

Last edited by HVAC RETIRED; 06-13-13 at 01:17 PM.
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Old 06-13-13, 04:18 PM
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I heard back from the contractor, he said he would come by and fix it tomorrow. Not sure what fixing it means, but I imagine he will drop the return lower and center it. HVAC retired, can you elaborate on what you just said, but explain it like I'm 5? So the XL14c( that is outside )has a return air filter ?, and then there is another air filter (pictured on original post) on the inside, and you're suggesting removing the filter from the unit outside, and adding an additional one on the inside? or a different air filter on the inside entirely?
 
 

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