# Would a 200mm fan be 2x as powerful as a 100mm fan, or 4x?

#### ChorniyVolk

##### Senior member
I was thinking roughly 4 because in the space of a 200mm fan you can fit 4 100mm fans, but what do I know.

#### cbn

##### Lifer
http://en.wikipedia.org/wiki/Circle

Well the total area of a 200mm fan is 4x greater, but the actual length of the fan blades is what matters more.

I would be inclined to say a sinle larger fan is much more space efficient (provided the center spindle is the same size as on the smaller fans).

For example on the 80mm coolermaster fan (see link below) the center spindle (with logo on it) proportionally takes up a lot of space.

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#### ChorniyVolk

##### Senior member
Right, I feel stupid.

Alright, so just 2x then, assuming the center spindle is the same size on both.

Going at the same speed, it provides 2 times the power. Would it provide an equal amount of noise or would it create less/more?

#### corkyg

##### Elite Member | Peripherals
Super Moderator
Normally, the larger fan turns at a slower speed, thus making less noise for the same CFM. That is the main advantage - quieter.

#### mentalcrisis00

##### Senior member
It also depends on the RPMs the fan is spinning at. Generally the higher the RPM the more air it moves, but that also means that it's more noisy. In theory the larger fans have more surface area so should be able to push more air than smaller fans at the same RPM. The advantage to the larger fans isn't so much how much air pressure they create, it's the larger airflow pattern they produce and the reduction in noise as corkyg stated above.

#### cbn

##### Lifer
Right, I feel stupid.

Alright, so just 2x then, assuming the center spindle is the same size on both.

Going at the same speed, it provides 2 times the power. Would it provide an equal amount of noise or would it create less/more?

No area is still what matters. But we need to calculate that using just the length of the fan blades.

#### Rubycon

No area is still what matters. But we need to calculate that using just the length of the fan blades.

There's a lot more to factor besides swept area and pitch!

Generally larger fans are used to provide similar airflow that you would have with smaller fans running faster (and louder!), The advantage is acoustics. Where one may find the noise from a few 120s objectionable the single 200 may provide similar cooling results either inaudibly or at acceptable levels. This is what makes the HAF series popular. Right out of the box they are reasonably quiet and decently cool.

#### cbn

##### Lifer
There's a lot more to factor besides swept area and pitch!

Generally larger fans are used to provide similar airflow that you would have with smaller fans running faster (and louder!), The advantage is acoustics. Where one may find the noise from a few 120s objectionable the single 200 may provide similar cooling results either inaudibly or at acceptable levels. This is what makes the HAF series popular. Right out of the box they are reasonably quiet and decently cool.

If we take swept area of the fan blades into account theorectically a 200mm fan could provide more than 4x the airflow of a 100mm fan right? This assuming the rpm and pitch of the blades were the same.

Of course with the 200mm fan that center section containing the spindle might have to get larger (reducing fan blade length within the shroud).

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#### Rubycon

If we take swept area of the fan blades into account theorectically a 200mm fan could provide more than 4x the airflow of a 100mm fan right? This assuming the rpm and pitch of the blades was the same.

Of course with the 200mm fan that center section containing the spindle might have to get larger (reducing fan blade length within the shroud).

Possibly but then you have to factor in static load. The only way for sure is to mount them and run some balometric tests. :hmm:

#### Itdbclos

##### Junior Member
Assuming both fans are running at 900rpms. The linear velocity of the outside edge of the 200mm fan will be moving at 180,000mm/minute while the edge of the 100mm fan will be moving at 90,000mm/minute. But the bigger fan will weigh a little more and be harder to spin.

#### Red Squirrel

##### No Lifer
I find big fans have a lower frequency noise which is less annoying even if they are spinning same speed as a 80mm one. It's more of a white noise then a whine. The worse is 40mm fans, those should be banned! lol. Super high pitched grinding noise and you almost want to take cover so pieces of plastic or bearings don't come flying out. I've never seen a 40mm fan where the bearings don't fail within a few hours or are already failed out of the box.

What I'd be curious to know is what is better to combat a high static load, a single big fan or many small ones. I'm thinking many small ones may work better, but what do I know. The design of the blades probably is a bigger factor. "blower" type fans probably have more static force then regular blade ones. HVAC systems used squirrel cage blowers for good reason, and not just a fan (which would be easier to make).

#### wwswimming

##### Banned
once i procured a fan that was about 4" in diameter & 4" long, to air-cool a radar tube. the radar tube put out 1000 watts heat average. it was a 10 kW coupled-cavity tube.

the fan cost \$5000.

the new engineering manager got so pissed off about the fan that he had me transferred to another department. they tried using everything else but ended up using the \$5000 fan. it was designed for a 4" duct and was entertainingly loud.

#### Rubycon

once i procured a fan that was about 4" in diameter & 4" long, to air-cool a radar tube. the radar tube put out 1000 watts heat average. it was a 10 kW coupled-cavity tube.

the fan cost \$5000.

the new engineering manager got so pissed off about the fan that he had me transferred to another department. they tried using everything else but ended up using the \$5000 fan. it was designed for a 4" duct and was entertainingly loud.

I'm glad you included the most important part!

People are obsessed with making PCs quiet. This is why I refuse to sleep next to a computer.

#### ChorniyVolk

##### Senior member
I have another question, is the whole positive air pressure thing notable? What I mean is, if there are more intake fans than exhaust fans, then the air has to push out of other holes in the case, whereas if it's reversed then the air has to be brought in through other holes in the case. The difference with the air being pulled in from other holes is that those holes may not have a filter which would mean dust and other crap would be pulled in, whereas with the air being pushed out of those holes it makes sure that there isn't any dust and other stuff in the case by pushing out in the areas where that stuff would normally creep in.

Also, consider the ATCS 840 http://www.newegg.com/Product/Produc...82E16811119187

If I stuck a 120mm fan on the internal drive cage, would that ruin the airflow to the top of the case where it's exhausted considering that the fan would blow the 230mm's intake air into the little crevice-like area between the video/sound/etc cards and out of the back instead of letting some of it flow up in the open area between the motherboard and internal/external drive, and then along all of the motherboard as it is exhausted at the top?

Or am I just crazy?

#### wwswimming

##### Banned
I'm glad you included the most important part!

People are obsessed with making PCs quiet. This is why I refuse to sleep next to a computer.

the specs i remember are "5 inches of water" (pressure spec) and "120 CFM" (cubic feet per minute). into free air it would push a lot more than 120 CFM.

once i cut my finger by trying to catch a 9" fan that drew 235 watts, that fell off a workbench. not my smoothest move, but, hey, that's how you learn !

#### Rubycon

the specs i remember are "5 inches of water" (pressure spec) and "120 CFM" (cubic feet per minute). into free air it would push a lot more than 120 CFM.

once i cut my finger by trying to catch a 9" fan that drew 235 watts, that fell off a workbench. not my smoothest move, but, hey, that's how you learn !

5in Hg is quite a lot of static! Then again we're talking about a real fan.

#### Modelworks

##### Lifer
Everyone always focuses on CFM, static pressure never gets any attention and is a sad panda

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