Increasing airflow to a single register.

[robertc65]

The run that supplies the register in my family room is a 5" round metal duct tapped off the top of the main trunk. All though it could be a strait shot it takes a few turns so it can be run parallel to the center beam. I could easily re-run this so there is only the turn at the takeoff on the top of the trunk and the turn up into the register boot. It looks like I would be removing four 90-degree turns and about 8 ft. of pipe. The strait line distance between the trunk and the register is about 22 ft. With the extra pipe in there now it is over 30 ft. Can this have much of an effect on the airflow? This register does not seem to blow much air compared to many of the others and this room could use some additional cooling. Just incase it matters I will mention that the HVAC unit is on one end of the trunk and this takeoff is on the last taper on the opposite end of the main trunk. It's not the last takeoff, there are two more after it. If I ran this as a strait shot could it make much of a difference in the airflow to this register?

Thanks in advance

Rob

[t527ed]

if you need more air get it as straight and short as possible, going up in size would also be a good idea unless the room is the size of a closet.

[dash]

It will help,but may not be enough,Manual D calculation would tell for sure.

I agree go to 6" if you do it.

[mchild]

Go with 6" and use a take off that has a damper so you can control the amount of air flow if it end up being more than you need. Registers alone can not dampen air flow sufficiently.

[dash]

Go with 6" and use a take off that has a damper so you can control the amount of air flow if it end up being more than you need. Registers alone can not dampen air flow sufficiently.

We find the register dampers, in a proberly designed system ,can reduce air flow by 30% without ill effects.

[mchild]

We find the register dampers, in a proberly designed system ,can reduce air flow by 30% without ill effects.

dash,

But wouldn't you prefer a damper at each take off or branch for overall better control?

[cem-bsee]

shoot, go up even 1 more size!

use 45 ells

controling fluid flow at either end of a pipe is ok, IF
the pipe & fittings sealed against leaks.

air is a fluid! -- so far as handling the calculations & flow

[dash]

dash,

But wouldn't you prefer a damper at each take off or branch for overall better control?

With Florida ducts being in attic,dampers leak and sweat,plus most don't want to go in the attic.So design becomes critical,IMHO,so you can avoid going in the attic.

[hvaclover]

With Florida ducts being in attic,dampers leak and sweat,plus most don't want to go in the attic.So design becomes critical,IMHO,so you can avoid going in the attic.

Never knew that.

Around here six in round with a damper is the norm and the code.

[robertc65]

Thanks for all the responses. I'll re-run this with a 6" strait shot to the register boot and see how it goes. I have had a couple of HVAC techs tell me that they would never use 5" pipe.

My house is only 9 years old and for some reason all the runs are 5". The ones going up to the 2nd floor are 5" oval. I don't think any of the upstairs registers deliver enough air and it is always a lot hotter up there. One day I plan to deal with the upstairs, but with all 5" going up there I imagine I will be looking at a system in the attic or running a trunk up to the attic and delivering the air via celing registers.

Thanks again

Rob

[renaissanse man]

We find the register dampers, in a proberly designed system ,can reduce air flow by 30% without ill effects.Ill effects also include air noise, which is what you'll get when dampering at the register.

[Atticmonkey777]

Mebbe adding an in-line booster fan after re-doing that run will help boost more air as well. ;)

[hvaclover]

Mebbe adding an in-line booster fan after re-doing that run will help boost more air as well. ;)

I hopee yo're kidding, those things are as useful as udders on a boar.

[cem-bsee]

come off side of trunk & use 45s to get most of duct up out of way --

did you run calcs?
or just want to guess?

[robertc65]

come off side of trunk & use 45s to get most of duct up out of way --

did you run calcs?
or just want to guess?

Thanks for the tip. I was about to ask if it would be better for the takeoff to exit from the side of the trunk. It appears that the bend would be much less than the hard 90 degree turn it takes now going strait up and then over.

I did not run calcs. I understand the importance of relying on calcs when designing a system or making significant modifications. My system is in need of some serious re-engineering, but for now I just want to get some more air in the family room until I can determine the best way to go about improving the entire system.

Thanks again

Rob

[dash]

I hopee yo're kidding, those things are as useful as udders on a boar.

Not that this job needs one ,but there are ones that are quiet and actually deliver the air flow.

check here;

www.fantech.net

[deejoe]

The info you have been given by dash and others should be of some great help. To sum it up;
Get rid of those 90's,make the run streamlined as possible
Perhaps installing a 6" run in place of this 5" will even do the trick.
And if it don't, try "SLIGHTLY dampering down some of the other runs that have good air delivery. (note the word "slightly") this will help increase air flow into this family room run.
Aso make sure there is some RETURN air in this family room.(very important)
Good luck.

[robertc65]

The info you have been given by dash and others should be of some great help. To sum it up;
Get rid of those 90's,make the run streamlined as possible
Perhaps installing a 6" run in place of this 5" will even do the trick.
And if it don't, try "SLIGHTLY dampering down some of the other runs that have good air delivery. (note the word "slightly") this will help increase air flow into this family room run.
Aso make sure there is some RETURN air in this family room.(very important)
Good luck.


Thanks for all of your help.

Rob