Should we address our ducting that feeds through our concrete block?

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Old 09-19-13, 06:15 AM
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Should we address our ducting that feeds through our concrete block?

Hi there, our upstairs bedrooms have very low airflow coming out of the ducts. We have a split level house, and the furnace blower is in the bungalow part of the house. The basement in the bungalow part of the house has a 7' high ceiling. The basement in the two storey party of the house has about a 3 1/2' high ceiling.

The furnace feeds the upstairs bedrooms through ductwork that goes through the concrete block as shown in the attached photo.

I had a guy come yesterday who has specialized in residential / commercial HVAC duct systems for 35 years, to suggest that there is a lot of airflow lost before the air even gets past the concrete block, due to the way the ductwork angles up from the furnace, and then angles down at about a 45 degree angle. He suggested that smoothing this out will significantly improve airflow, in addition to applying mastic on all duct joints. Right now it's quite obvious that the old foil tape, and complete lack of sealant in other ductwork joints, is probably contributing to loss of airflow.

At this point I need to validate the theory that the ductwork coming out of the furnace, and then angling down, is contributing to a large loss of airflow. What do you all think? I wonder how much airflow is lost, and if it's significant enough to merit the cost of improving it. Also it is something DIY-able? I don't know anything about ductwork and don't want to get in over my head...

Thanks!
 
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Old 09-19-13, 09:32 AM
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Dont think taping are making the duct straighter is going to help much. You might pick up 50 cfm at best. ID call another company and get them to do a heat load on the home. this will tell them how much air they need for each room and they can size the duct correctly.
 
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Old 09-19-13, 11:55 AM
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Ok, I called another HVAC contractor who will stop by next week to have a look. Do you think the guy who came in then and just suggested doing this might not really have the best ideas? Since he didn't take any airflow measurements or anything? He is more of a sheet metal guy that some HVAC contractors sub work out to.

Do you think that it's even worth sealing the ducts w/mastic? Many of them are not sealed at all, and where they are, often the foil tape has come apart.

Thanks
 
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Old 09-19-13, 02:39 PM
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Any duct that goes into the crawl space should be sealed. The basement would be considered conditioned space and would not have to be sealed, unless the return filter is up stairs and not in the unit.

Id say with out a true heat load nobody can figure out what to do. My guess is the duct is to small to begin with. What is the size of that duct?
 
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Old 09-19-13, 02:42 PM
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size at its smallest point
 
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Old 09-19-13, 08:52 PM
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The furnace has 2 main runs leaving it. The ductwork to the bungalow area of the house is 12 x 8". The ductwork to the 2 level side of the house, that goes through the concrete block, is 16 x 8" at its smallest.

Our house is a 2,300 sq ft above grade. Basement is about 700sq ft at 7' height, then about another 700sq ft at 3 1/2' height (in the crawlspace area). The furnace is installed in the bungalow of our split level. The bungalow side of the house above grade is about 700 sq ft. The 2 level side of the house is the other 1,600 sq ft above grade.

I'll be sure to properly seal it all, thanks airman.
 
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Old 09-20-13, 09:45 AM
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Also, the ducting that goes upstairs from the crawlspace is via 5" diameter circular ducts
 
 

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