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Not Enough Air Flow...

 
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Old 05-15-2011, 08:17 PM   #1
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Not Enough Air Flow...


There was an extention put on this house 20 yrs ago, and for a/c and heat flow they just tapped off the two lines from the adjacent room. The lines are 6" round for about 16' then run down the wall to a register with square ducting. They tapped in before it turned down with another 6" pipe for about 6' the put a vent. This is in two locations. There is'nt really sufficient flow in the extention but in the adjacent room it seems ok.

Question: can i put a draft inducer or in-line booster on each of the lines before both vents? Will this be ok for the unit?

Last edited by Premier_929; 05-15-2011 at 08:33 PM.
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Old 05-16-2011, 04:43 AM   #2
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Re: Not Enough Air Flow...


You can. But it still may not be enough air. Might want to try running larger duct from the main to the area where they split the ducts first.

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Old 05-16-2011, 11:25 AM   #3
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Re: Not Enough Air Flow...


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Originally Posted by Premier_929 View Post
There was an extention put on this house 20 yrs ago, and for a/c and heat flow they just tapped off the two lines from the adjacent room. The lines are 6" round for about 16' then run down the wall to a register with square ducting. They tapped in before it turned down with another 6" pipe for about 6' the put a vent. This is in two locations. There is'nt really sufficient flow in the extention but in the adjacent room it seems ok.

Question: can i put a draft inducer or in-line booster on each of the lines before both vents? Will this be ok for the unit?
it would not work.......the right thing to do is increase the amount of main trunk line, and run off the main trunk to the exstension.
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Old 05-16-2011, 01:30 PM   #4
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Re: Not Enough Air Flow...


My inline just barely works for a cold family room on a slab, but it had some increase of noise at the destination end, even with a fabric decoupler in the duct. You have to turn up the TV sound slightly when the heat comes on.

After some years the tape on the shaded pole fan motor winding came loose and hit the fan blades, but this was easy to troubleshoot and repair.

If the cost of an installed fan is X% the cost of other repairs, the chance of the fan fixing the problem should be at least X for you to take this gamble.

E.g., other repairs = $500, installed fan is $100, install the fan if the chance of it fixing the problem is at least $100/$500 = 0.2 = 20%.

With more info & data these odds can probably be accurately estimated.
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Old 05-16-2011, 02:27 PM   #5
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Re: Not Enough Air Flow...


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My inline just barely works for a cold family room on a slab, but it had some increase of noise at the destination end, even with a fabric decoupler in the duct. You have to turn up the TV sound slightly when the heat comes on.

After some years the tape on the shaded pole fan motor winding came loose and hit the fan blades, but this was easy to troubleshoot and repair.

If the cost of an installed fan is X% the cost of other repairs, the chance of the fan fixing the problem should be at least X for you to take this gamble.

E.g., other repairs = $500, installed fan is $100, install the fan if the chance of it fixing the problem is at least $100/$500 = 0.2 = 20%.

With more info & data these odds can probably be accurately estimated.
the ducts are improperly installed............the will never work the way they are now.............you can put lipstick on a pig, but its still a pig.
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Old 05-17-2011, 07:26 AM   #6
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Re: Not Enough Air Flow...


What kind of takeoff does the branch line have? A round or a heel boot to round takeoff? If it is just a round takeoff you might try the 45 degree heel boot to round takeoff.

In our training lab we have a mix of takeoffs on our airflow trainer where students can see and measure that the simple round takeoff is the least desirable for airflow.
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Old 05-17-2011, 08:42 AM   #7
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Re: Not Enough Air Flow...


And here I thought that "oink, oink" noise was coming from my furnace. . .
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Old 05-18-2011, 07:46 PM   #8
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Re: Not Enough Air Flow...


Thanks for all your ...um input. I opened the ceiling and saw there is a 6" elbow coming out the top of a 12 x 12 main trunk. comes about 12' to a T, down the wall sqaure to vent and one straight to the extension about another 6'. I tapped into both the 12' lines about half way and put in a 250cfm Booster.

My question now is where do I wire them to. I obviously want them to come on whenever either the heat or the a/c comes on.

thanks
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Old 05-19-2011, 09:30 AM   #9
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Re: Not Enough Air Flow...


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I obviously want them to come on whenever either the heat or the a/c comes on.
You need a "sail switch".

BTW, I would go with a multi-speed fan; it lets you trade off comfort vs. noise.

Last edited by GettingBy; 05-19-2011 at 01:10 PM.
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Old 05-19-2011, 05:44 PM   #10
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Re: Not Enough Air Flow...


Found it , thanks.

Last edited by Premier_929; 05-19-2011 at 05:52 PM.
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Old 05-19-2011, 05:49 PM   #11
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Re: Not Enough Air Flow...


No, but an HVAC guy or the manuf. can probably give you guidelines.

I'd guess you'd want the minimum sail area that will work at the minimum CFM in the duct and the switch contact ratings have to be able to handle your duct fan motor current draw.

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