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-   -   Return Register Size for 16" Flex (http://www.diychatroom.com/f17/return-register-size-16-flex-31767/)

hartkem 11-13-2008 07:34 AM

Return Register Size for 16" Flex
 
What size return register do I need for 16 inch flex. There will be one register centrally located in the hall way.

Marvin Gardens 11-13-2008 10:22 AM

600 sq in should work (depending on the cfm's in the flex duct).

Keep in mind that it is not about size, it is about cfm's pushed through. A 16 flex can have anywhere from 0 to 10,000 cfm's or more. Average would be about 1800 cfm's.

If you want to do it correctly (and don't have the tools) you should total the cfm of your furnace, divide the total inches of duct work, and multiply that times the volume of each duct to get an idea of how much is flowing through each duct. Then you could find a reasonable idea of how much air is going through the 16. Then you could get a more accurate idea of how big the return should be.

It is usually better to go bigger if in doubt. Starving a furnace for return air is a good way to shorten it's life and decrease it's efficiency.

hvaclover 11-13-2008 02:55 PM

Quote:

Originally Posted by Marvin Gardens (Post 184269)
600 sq in should work (depending on the cfm's in the flex duct).

Keep in mind that it is not about size, it is about cfm's pushed through. A 16 flex can have anywhere from 0 to 10,000 cfm's or more. Average would be about 1800 cfm's.

If you want to do it correctly (and don't have the tools) you should total the cfm of your furnace, divide the total inches of duct work, and multiply that times the volume of each duct to get an idea of how much is flowing through each duct. Then you could find a reasonable idea of how much air is going through the 16. Then you could get a more accurate idea of how big the return should be.

It is usually better to go bigger if in doubt. Starving a furnace for return air is a good way to shorten it's life and decrease it's efficiency.


Marv 10,000 cfm is 25 tons of cooling. You won't get that thru 16" flex pal:eek:

Marvin Gardens 11-13-2008 04:44 PM

Quote:

Originally Posted by hvaclover (Post 184392)
Marv 10,000 cfm is 25 tons of cooling. You won't get that thru 16" flex pal:eek:

I know, but with enough force you can shove anything through.

Plus it would be really windy. :yes:

hvaclover 11-13-2008 04:49 PM

Quote:

Originally Posted by Marvin Gardens (Post 184453)
I know, but with enough force you can shove anything through.

Plus it would be really windy. :yes:

10,000cfm thru a 16" metal flex would blow like a hand grenade.

It has never been done nor would it ever be considered.

Marvin Gardens 11-13-2008 05:12 PM

Quote:

Originally Posted by hvaclover (Post 184456)
10,000cfm thru a 16" metal flex would blow like a hand grenade.

It has never been done nor would it ever be considered.

I was just giving an example.

Size of return is all dependent on the output of the furnace.

If you look at the other end of my example I had 0 CFM. In that case there would be no need for a return, right?

hvaclover 11-13-2008 06:08 PM

Quote:

Originally Posted by Marvin Gardens (Post 184465)
I was just giving an example.

Size of return is all dependent on the output of the furnace.

If you look at the other end of my example I had 0 CFM. In that case there would be no need for a return, right?


Sorry but it was just too much for a layman not to accept at face value.

Marvin Gardens 11-13-2008 06:26 PM

Quote:

Originally Posted by hvaclover (Post 184481)
Sorry but it was just too much for a layman not to accept at face value.

I suppose when I give examples they shouldn't be that extreme. But being that extreme drives home the point for sure.

I tell my paramedic students to never start in intraocular IV. That gets them thinking and some figure it out and some don't. There is no such thing as in intraocular IV since that means sticking a needle in the eyeball and running some fluid or drugs in there. :whistling2: DON'T BLINK, DON'T BLINK!!!!!!!

8 Ball 11-13-2008 07:35 PM

Flex for a return...not the best choice.

1610 CUB 11-14-2008 09:06 AM

10,000CFM at 7,500FPM = 16" used only to suck up small children and pets. Some industrial application's may apply.

hvaclover 11-14-2008 09:42 AM

Quote:

Originally Posted by 1610 CUB (Post 184775)
10,000CFM at 7,500FPM = 16" used only to suck up small children and pets. Some industrial application's may apply.

And duct cleaning....

Marvin Gardens 11-14-2008 09:42 AM

Quote:

Originally Posted by 1610 CUB (Post 184775)
10,000CFM at 7,500FPM = 16" used only to suck up small children and pets. Some industrial application's may apply.

We call that a shop vac on steroids.

hvaclover 11-14-2008 10:10 AM

Quote:

Originally Posted by Marvin Gardens (Post 184488)
I suppose when I give examples they shouldn't be that extreme. But being that extreme drives home the point for sure.

I tell my paramedic students to never start in intraocular IV. That gets them thinking and some figure it out and some don't. There is no such thing as in intraocular IV since that means sticking a needle in the eyeball and running some fluid or drugs in there. :whistling2: DON'T BLINK, DON'T BLINK!!!!!!!

Does this mean i can't inject my back pain meds in my tear ducts anymore?:jester:

Marvin Gardens 11-14-2008 10:26 AM

Quote:

Originally Posted by hvaclover (Post 184807)
Does this mean i can't inject my back pain meds in my tear ducts anymore?:jester:

If you can stick a needle in your eyeball you are a better man than I. :laughing:

beenthere 11-14-2008 05:11 PM

Guess you wouldn't like the 6" pipe that has 2000CFM moving through it.

This pipe runs 300', and has a 100 hp blower on it.
It also travels several foot into a treatment tank.
And runs at 5PSIG static presure. :)

If you got the Horse Power, you can move as much air as you want through a small pipe.


O P. How much air do you want this 16" flex to move.


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