You can mix and match.

ok thanks

Look at the CFM rating or the m³/h rating, it tell's you how much air the fan will push/pull.

I'd rather good fans pushing or pulling more air than slow fans doing worse.

speeds depend on the fan controller or the port on the mobo they are plugged into

use bios to set fan speeds according to cpu/socket temp or sb temp

if the fan is 3pin fan header or molex/sata its dc voltage control
if the fan is 4pin fan header its pwm
set bios accordingly to the fan type that is plugged into each port

would different fans running at different speeds make the system sound bad?

fans at full speed will be loud
find a balanced speed/temp profile for case and cpu/gpu fans

generally low/off at 40c to 100% at 90c

Originally posted by Bryan999:

first time building pc and wondering if its best to have all the same case fans so that they all spin at the same speed or is it ok to mix and match.

Ideally yes.
I suggest a case with quality fans included.
I have the fractal torrent tower case.
Included fans, with excellent airflow and a fan hub with it.
When the fans eventually wear out, I can replace with the most suitable ones available at the time.

The case is the only really 'future proof' part of a PC.

Other cases have came out since that one thought.

I have my water pump fans in the cpu slots, while the other five fans on the fan hub

i have already got the nzxt h7 flow 2024 so i need the fans for that.

If your fans comes with lights thats another layer

ok thanks

Look if they have PWM. So you can regulate how fast they are. Also look at their millimeters size, like default 120/140mm.
Bigger fans can move more air, but less air pressure.
Big fans are nice as exhaust fans...
*PWM is optional.*

Originally posted by Bryan999:

would different fans running at different speeds make the system sound bad?

It's the other way round, when all your fans sync up it can cause harmonic resonance.

Originally posted by Im smoking gas:

Look if they have PWM. So you can regulate how fast they are. Also look at their millimeters size, like default 120/140mm.
Bigger fans can move more air, but less air pressure.
Big fans are nice as exhaust fans...
*PWM is optional.*

mobo headers can be set to pwm for pwm fans, or dc voltage control for non pwm fans
you just need to set the header and fan profile in bios for the fan type connected to it

ok thanks for the replies, i was looking at a set of the ARCTIC P14 Pro PST pack of 5 for £27 but they have gone out of stock, i was also looking at the be quiet Pure Wings 3 140mm PWM Fan model BL108 at £9.95 each.