Replacement CPU Fan for: P4-- 2.4 GHz: minimum CFM I need?

I have a Pentium 4, 2.4 GHz CPU, Socket 478

I want to replace my Fan, for the 2nd time, with a still quieter one—
What is the minimum &/or recommended CFM [cubic feet per minute]I need?

I don’t play video games or watch movies or anything I believe is CPU intensive.
I ask the minimum CFM because: the less air volume, the quieter the fan tends to be.

----
1]The current Fan is 20 CFM , 36.5 dB, 60 x15 mm.
The heat sink is 60mm x 60mm x 35mm w 42 fins of skived aluminum.

2]The original Fan was 24.4 CFM , 40 dBA [& heat sink ] by Dynatron.

A larger fan will provide as good or better cooling at a lower RPM & should produce less noise. Or if you have the room for it, you could try something like this:

http://www.svc.com/cod1ae4licpu.html

ASUS A7N8X-X
Athlon XP 1800+
8.5 x 200MHz
1024MB PC3200 2.5-3-3-7
Asus A9550GE/TD 128MB
WinME/WinXP Pro SP1

I figured your goal is to cut all noises to the barest minimum, if that's the case have you considered a fanless cooler like the Nitrogon.

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Thanks,that's my plan: to use a fan of greater height: a 25mm case fan to replace the 10mm height CPU fan I have.

I'm assuming that if the CFM's are the same the cooling will be equal, even if the RPM's are lower.
[And I also hope to use the minimum CFM's I believe safe for my application.]

Is all this going to work correctly?

Corrections to my post above-- should read:

I want to replace my 15mm height CPU fan,with a quieter, 25mm height [it's a small "case fan" --same base size as mine].
----------------------
Additions :

I can get this relacement fan for just $3.75, but it's 19-21 CFM's which may be a bit low?

or another fan for $6 that's 18 CFM, but very quiet--only 23 dB-- hence my question!

I was thinking you'd replace the entire heatsink/fan combo & go with something that has an 80mm or 92mm fan rather than a 60mm.

ASUS A7N8X-X
Athlon XP 1800+
8.5 x 200MHz
1024MB PC3200 2.5-3-3-7
Asus A9550GE/TD 128MB
WinME/WinXP Pro SP1

I don't know how that would fit --
the fan must have a 60mm square base to fit the 4 screw holes on the Heatsink.

Refer to last post about replacing the ENTIRE heatsink and fan assembly (as long as they fit in your computer)

Rule #1 Good computers don't go down.
Rule #2 There is no such thing as a good computer.

http://www.svc.com/di4-8kd3b-0l-19.html

http://www.svc.com/cod1ae4licpu.html

http://www.svc.com/pct-cpu5700.html

ASUS A7N8X-X
Athlon XP 1800+
8.5 x 200MHz
1024MB PC3200 2.5-3-3-7
Asus A9550GE/TD 128MB
WinME/WinXP Pro SP1

Thanks! to jam & Rick,
Having looked at the low priced, xlnt, CPU coolers from SVC I'll have to think about replacing the ENTIRE heatsink and fan assembly.

My heatsink is a Dynatron held against the CPU by a clip which appears to be attached to 4 holes in the MOBO.
I have no experience here:
Is it common/easy to be able to go to a larger heatsink?