What is the correct water cooling fan for a Asus Intel i7-4790s?
Gift for my son. I know nothing about this.
Short answer - Corsair H100i or H80i, but go to a Best Buy location and chat up a PC builder first before pulling the trigger.
Not so short answer-
This depends exclusively on the case. The i7-4790 desktop processor is what's called a Socket LGA1155, which means that any fan or water-cooling assembly designed for that shape of a processor socket will work fine. Most modern ones will do this with no trouble, and are actually modular enough that they will work with anything going back about two generations both AMD and Intel.
There are a few VERY important things to remember though, when choosing and installing a radiator.
1. Will it fit?
-YOu need a bay for your radiator. Most radiators will be sized similarly to single or grouped fans, usually either 120x120mm (one 120mm cooling fan) or 120x240mm (two 120mm cooling fans). Some high-performance gaming cases offer a special spot to install this inside the top. You can't always tell without looking inside, so a great way to tell is simply to find the model of your son's case, type that name into Google followed by "Compatible with" and the make and model of your radiator unit.
2. Where am I going to mount it?
-In a top-mount radiator, this is an easy solution. Some fancy aftermarket cases offer more unusual mount locations, though in the case of many standard machines with a 120mm exhaust fan, a 120mm single-style radiator might be all you can fit. THis is not always ideal, since that exhaust fan will either be replaced with a radiator (which then gets hot air pumped through it) or ends up getting reversed (which means you no longer really have an exhaust for hot air). Another potential issue is that you may have to remove the backplate of the computer to install the pump's bracket. The process is actually pretty easy and most pumps self-index pretty well to prevent any kind of mounting problems, but if your case does not have a removable backplate that exposes the *back* of the motherboard, installing this unit will require the entire machine be disassembled, which is a pain.
3. Why water?
-Water cooling is a godsend for high-performance machines, but in many applications, air cooling can be as good or better. Air cooling takes up less electricity, which means less amps drained off of your PSU. Air cooling has fewer failure points and is often cheaper. Water cooling has a very distinct advantage of being able to remove a staggering amount of heat and maintain a very consistent core temperature without generating a lot of noise, however, so if sound is a concern, then you're on the right track.