DUCTING TIPS{My Experences}

I have posted in posts about ducting but wanted to share what I found in making efficient ducts.I have ducted 3 different systems using cans,cardboard,dryerhose,flex ribbed metel hose,And PVC pipe Reducers.I have done straight,and curved ducts.This is what I have learned in all these setups.

The Duct MUST provide more air in a unrestricted mannor than the fan can push.So the supply Must exceed the fans output.And there needs to be zero effort on the fan to collect it's air.No different than if the fan was running on a table.

By extending a 60mm fans inlet several inches by putting cardboard on the fans four sides does not increase its air supply but rather creates a vaccum like effect.By doing this Tunnel type duct you can actually reduce the fans output and cause the fan to work on obtaining it supply of air.

So I have learned with different attempts that my 60mm fans @30cfm work great with an 80mm duct or larger.This set up prevents the sinkfan from working to get its air.And because the fan is not under load it is quieter.

Also the straighter the Duct the better.Because you do not want the sinkfan to pull its air supply.As for ribbed ducts these introduce turbulance so if used you should consider a very large duct to reduce the effects of the turbulance.Also curved ducts can create the fans need to Draw its supply and the curved ducts are Mostly RIBBED hose.So here you have 2 issues to deal with turbulance and curves.

I know most people think you must provide a seal between heatsink fan and the duct,This is untrue.My ducts cover 2/3 of the fans height making it so the fan is inside the duct,But the ducts are not so deep as to allow the air pushed over the heatsink to reenter the duct. Also In my setup I have 2 case fans blowing directly onto the motherboard as well as 4 exhaust fans pulling the air out.Making for a steady flow of air.

Now how do you attach a big duct to a small fan?And how does a large duct allow the fan to get its air exclusivle from the duct and not the case air ?

Easy the duct or ducts in my box are attached to the case side with L brackets the ducts are PVC and are straight.The ducts are 3.75 at the heat sink fan and 3.0 at the case side inlet.And easly slide over the heat sink fans.When assembled my fans which are approx 2.5 inches sit in a 3.75 inch duct.This duct covers only approx 2/3 of the fans total height.Allowing the fan to gets it fresh air but not redraw warm case air.And avoids any tunnel like sides on my fans.

So there it is my experences with ducts.The cost of this is under 20.00 dollars the benifits of good ducting have been for me a reduction of 8c.And by installing Quiet sink fans I run at a MAX of 40 to 41c.If I use my 38cfm screamers my temps drop to 39c but the noise of 2 screamers aint worth the little benifit thay give me.

In the case mod gallery page 7 at the top is a picture of my ducts.Also if any one needs more info ask here and I will post a reply.

Thanks for all the great informations...

I have a question...
How would you design a air duct for users using heatsink with fan sucking air ?

Sucking air ? do you mean sucking off the heat sink and blowing into a duct.


Or do you mean getting air from a duct and blowing onto the heat sink.

My system gets its fresh air from the duct and blows it onto the heat sinks.

I think that xxgg means how do you duct fans on HS's that draw air up and through the HS? Like most Alpha's do.

It would be great if simply reversing the direction of air flow through a CPU duct would do the trick. If only life were that simple..

diehrd said:

Ok here is the link ....This link takes you to there cover page select gallerys, main page at bottom.



http://casemod.tripod.com/

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here as diehrd explains you can see the ducts over his processors (they are those round pipe like things on the inside of side panel)

xxgg:
I would (and I will as i have an exhaust duct for a slot fan sucking through my CPU heatsink and I'm not completely happy with it) do just the same diehrd does for intake fans: build an oversized duct and I will not seal it onto the fan and I will have the outlet inside the duct.

I bet it will be real good.

klosters64a said:

I think that xxgg means how do you duct fans on HS's that draw air up and through the HS? Like most Alpha's do.

It would be great if simply reversing the direction of air flow through a CPU duct would do the trick. If only life were that simple..

Click to expand...

It may be that simple I would try using a duct 3.5 inches around the whole lenght of it and have the duct mounted to the case side as I did.I Havent run tests on blowing out through the duck but it would make sense to have the duct bigger than the heatsink fan.

Also doing it like that means you will need a very good supply of air from the case fans.And for exhaust you need to deduct processors fan from total needed exhaust.

Kinda like this and this is an example only.
2x80mm Inlet approx 33cfm each

1x33cfm heat sink fan out let through duct.
1x80mm case fan out let. 33cfm

I have this question, diehrd:
A really different case. What if your fan blows into the duct not sucks from the duct?
(This is if you have, as many people, the duct on the case side panel and it blows into a duct that blows into the heat sink).

I'm not sure but I think in this case there should be a tight fitting between fan-duct-heatsink. This is the case for instance if you want to put an 80mm fan onto a 60mm heatsink and you want a long duct so it tappers softly and gradually from 80mm at side panel to 60mm at heat sink.

Do you have experience? What do you think?

I assume you are asking me if exhausting through a duct works well ? I cant see how unless you are intaking a lot of fresh air .

It seamed to me the trick is to get the coldest air you can to cool the heatsink.Therefore direct room air being forced down onto the heat sink seemd the best way.There is no chance of heating the air this way.
{My system has the fan Mounted to the heatsink in a stock style mount blowing down onto the heatsink as most heatsinks do.}

Your funnel idea may work 80mm to 60mm,But you are now making the fan work on getting the volume of air to the heatsink.So if you want the max air flow from the fan get a high cfm 80mm fan. I was looking for cool temps and quiet,as an option to water cooling.SO I use a 30cfm 32dba heatsink fan on each processor.And with a 38cfm screamer fan I shaved only 2c from max temps {39c,,41c}

As to the tight seal I find that a fan does not necessarly draw air from its center it actualy draws from the sides as well.Here is what I mean ,Hold a match to the right of a fan and it sucks the flame to it,Hold to the left ect and it sucks the flame to it.So I figured the way to maitain max intake was to allow the fan the closest way I could to resemble a fan running on a table top.

So to seal its sides and extend its inlet creates the need for the fan to work on getting its air reducing its output.Now of course this does not mean the system will run hoter all it meant to me was the fan is louder when it is under a load.

I hope this helps 2x1800Xp at 11.5x140 running at 41c MAX is really good considering it is 74 to 76 degrees in this room.And my goal was a quiet cool system with out the hassle and dangers of water which by the way are limited by ambient room temp as well.Also I spent less thn 20 dollars on the Mod and If I am 5c hotter then water I am doing great.{Personally I have not seen a dual XP1800 on water run at 36c ,have seen 40c as the average}

(semi-super-noob injecting his .00002 cents worth)

I've actually had quite a bit of fun with overclocking, but I must admit that the machine mentioned below is still running stock speed.

Regarding ducting: larger cross-sections, shorter routes, and fewer bends will always be the best. I just wanted to show off my choice of ducting to see what people thought of it:

http://www.isomedia.com/homes/color/oc/case008.jpg
http://www.isomedia.com/homes/color/oc/case009.jpg

I left just under a quarter inch of clearance over the fan, just in case I kicked the side ofhte case

The result was 9c cooler running, no load, stock speed, Athlon XP1800+, Soyo Dragon Plus, Enlight ATX mid tower case. EDIT: forgot to mention Swiftech MC462a.

The whole reason I was prompted to try it was the silly case I have doesn't really draw cool air in the front. There is a fan, but the decorative cover has such tiny holes, that most of the airflow into the fan is pulled down the front of the case from the drive bay area. So it all it was really doing was stirring up hot air.

Thats what I am saying,Big Big Big difference with direct DUCTS.!!!


That looks like one fine job !!

omaticrail:
Not bad, probably works quite well.
Just a little tricky when you change motherboard och cooler that doesnt fit etc.

Great tips, diehrd. What can you say about noise
concerning ducts?

omaticrail, I really like the looks of your duct. Very clean.
Your case looks like my Toshiba server. Same problems.

You guys ever look at HP ducts? They are usually curved
and have the fan in the middle i.e. there is part of the
duct on each part of the fan. AND, there is no fan on
top of the CPU Heat sink.

Tecumseh said:

Great tips, diehrd. What can you say about noise
concerning ducts?

omaticrail, I really like the looks of your duct. Very clean.
Your case looks like my Toshiba server. Same problems.

You guys ever look at HP ducts? They are usually curved
and have the fan in the middle i.e. there is part of the
duct on each part of the fan. AND, there is no fan on
top of the CPU Heat sink.

Click to expand...

Use a slower fan with less cfm and a lower DBA.I went from 38cfm 46.5 dba Screamers to 30cfm 32DBA fans and gained only 2c in max load temps.....

Have never seen them but for sure would like to do you have a link to a picture of them ???

diehrd said:

Have never seen them but for sure would like to do you have a link to a picture of them ???

Click to expand...

Sorry I have no link, but the next time I dust out the old HP
I will take a picture.

Seems I remember something from turbulence studies
about needing a fairly strait section before and after
a fan for best flow onto a heat sink. Obviously HP
does that, but I've never seen a personal mod do
that. It could be a space issue.

I lowered my temps by making a duct on both my computers. duron 800@958 full load temp is 32c and 1.4 [email protected] full load temp is 37c and thats at a room temp of 26c

res0r9lm said:

I lowered my temps by making a duct on both my computers. duron 800@958 full load temp is 32c and 1.4 [email protected] full load temp is 37c and thats at a room temp of 26c

Click to expand...

Thats impressive, that t-bird is almost as cool as mine.
Not so strange though since thats a pretty mean cooler u have
I also have a bitchy room temp around 26C.
I think I'll do a duct some time if i need to oc more, not with this cpu though cuz its stuck at 1118mhz

Adding A Fan to the duct

I added a large 90mm fan into the side of my case. My temperatures have gone down about 12 degrees C. Its nice and cold there now but I want to install a duct over my Athlon XP 1700 chip overclocked to the xp2000 (1.63ghz). Now lets say I had the duct over the heatsink like you are supposed to do. Would it be wise to add a fan on top of that duct to blow more air into the heatsink's fan? I have a Volcano 7 on it now. Let me know~!

If this link works follow the next button and you will see a duct that looks similar to the HP duct that the other guy was talking about.

http://www.newegg.com/app/Showimage...02-05.JPG/11-120-002-06.JPG/11-120-002-07.JPG

just lowered my temps a little more by removing heatsink fan and just using duct. duron dropped another 1c but the best thing is I can't here it now I need to do the same to tbird.