Understand fans specification help

[ste2425]

This is probably a short question but I'm looking to upgrade my very old fan collection to something that can still provide good cooling but doesn't turn my computer into a jet engine. My current fans are the same ones I bought when building my first pc and lets say I went for looks in choosing them and whilst my knowledge on the rest of my computer has grown I still have no idea about fans. I understand the dB ratings but the CFM is it for airflow. I have no reference so when I see fans stating this that and the other I have to idea if that's actually any good or not.
Hope you lot can just give a reference as to what level of CFM will provide good cooling. Thanks all

 

[Aquinus]

Higher CFM (cubic feet per minute) is the rate of moving liquid or gas. Higher numbers means more air flow, it's pretty simple. Some fans also rate static pressure which says how hard the fan can push that air rather than how much it moves (since it moves less if there is air friction.) All in all, the faster and more air a fan moves, generally it makes more noise.

I have a 100 CFM fan on my case and at full speed it sounds like a jet taking off considering it spins over 5000 RPMs when that happens, so I let my motherboard handle the fan speed so as CPU temp rises, the case fan will speed up where my already quiet CPU fan is running at 100% (since you really can't hear it).

 

[ste2425]

Thanks I understand the principle of what the rating means I'm after a reference, just like dB is referenced against zero you you know how loud or quiet anything else is. My current fans don't show any ratings and I have no idea how high the CFM rating can go upto so what I think could be a high rating could end up being tiny . Sorry I should have been more descriptive. Using the iPhone app and as it doesn't tilt to extend the keyboard typeing becomes very monotonous

 

[FordGT90Concept]

Usually fans have the amperage on the label. If you have an idea of what type of bearing the fan has, the two combined are pretty good for finding a close equivalent for replacing it. If this is an OEM computer, the CPU fan is usually a ball bearing and the rest are sleeve.

 

[Hood]

Fan-tastic

For case fans you want the highest CFM in your acceptable noise range ( most people say that anything below 40dB is very quiet). So in your fan size, you look for a fan with the best CFM rating below 40dB. Also, the larger the fan, the more airflow at the same noise level (in general). So if you can fit larger fans in your case (some old AMD thing?), that always helps. Look at the rated max RPMs, fans over about 2500 are pushing the 40dB limit. I always get over-spec fans and turn them down with a fan controller - that way you have the best cooling when needed and blessed silence the rest of the time. I have a Delta 92mm from an old Dell that spins at 6000 RPM and pushes 240 CFM. It sounds like the worlds largest dustbuster. Thankfully, fan technology is always improving, giving us more static pressure and airflow with less noise, through the use of advanced bearings and fan blade/frame shapes. Just read the specs and make your choice, but remember, you get what you pay for, and cheap fans with pretty LEDs are usually no bargain (rattling, over-rated airflow, under-rated dB level, etc).