At 8:30 it's a black screen as the video ends at 8:34but at 3:55 she is examining the case exterior and says you can mount a 240 radiator "on top" of the case. Externally or internally ? The presence of water cooling grommets at the rear top would seem to support an external mount, on top of the chassis but in the "attic" where the fans are. While that would accommodate a custom loop, you wouldn't be able to get the H100i's tubes if you had to go thru the grommets.
Looking at the 5:30 mark when she tips it up you can see the top motherboard standoff which does not appear to allow room for a radiator inside the chassis
This is supported by the the techpowerup review which shows the same standoff and states:
http://www.techpowerup.com/reviews/Antec/GX500/4.html
The ceiling is, as mentioned, filled with two more 120 mm units. All of the fans within the GX500 are identical and are set to pull air out of the case. There is no space to install a radiator here, but this case is probably not the one you would go for with a liquid cooling setup
Here we get little detail ... not sure I have seen the word "waiver" used before in this manner.
http://www.vortez.net/news_story/antecs_gx500_emerges_as_a_new_budget_challenger.html
* Radiator Mountings (partial waiver of fan slots):
- 1x max. 240 mm (top)
http://t4cam.blogspot.com/2014/04/antec-gx500-gaming-chassis.html
Kitguru writes
There is also a large vent in the roof of the case which covers two 120 mm exhaust fans … Antec include these with the case. There should be enough room here to install a 240 mm radiator if required, but we doubt most people shopping at this price point will be able to justify the cost of one.
Not sure what that means.... this appears to support the above the chassis and in the "attic" assumption made earlier. With the conflicting review statements, I am wondering if there are several versions of the case in existence.
here we get more support for the 240
http://www.dvtests.com/antec-gx500-test-review/
Although Antec GX500 is compatible with top 240mm water cooling radiators there was no way for me to install Silverstone Tundra TD02. Don’t be alarmed as probably a standard size and thickness radiator should fit perfectly on the top two 120mm fan mounts, it’s just that the TD02 is a large and thick radiator not suitable for smaller size cases.
Let's use some more pics from above link
So here's my final thoughts:
1. Looking at the first pic, I would say that there is little chance that you are going to fit an H100i **inside** the chassis with an ATX MoBo. Those top MoBo standoffs are just way too close to the top of chassis plate with the fan holes.
2. It would appear however that from statements made by reviewers you can fit a thin 240mm rad on top of the chassis in the "fan attic".
3. Now looking at the 2nd pic, it shows the top of the chassis with the fan holes as part of the chassis and it's unremovable. So while I can see that one could possibly fit a 27mm rad in there, how do you route a CLC's unremovable / unreplaceable tubes thru the top ? Where does the rad ports go since the top of chassis allows no opening for same ? Are the tubes long enough to go to the rectangular opening in the case, wrap around and back to the CPU ?
Given the above, my supposition is:
1. I'm sticking with the H100i will not fit inside the chassis. There does not appear to be adequate room possibly between chassis plate at the top (with the round fan cutouts) and the top of an ATX MoBo. Use a Micro ATX Mobo and that would eliminate this issue.
2. There appears to be enough room to fit a 240mm radiator w/ end ports in the "attic" where the fans are ... but not a CLC like the H100i as the rad ports are on the bottom (or top). The ports themselves likely won't fit above the chassis plate or below plastic top but the tube can't make a 90 bend in that small space.
3. In order to make this work, a significant case mod would be required. Openings would have to be cut to allow the tubes to get down from the "attic" to the case interior.
4. A thin 240mm radiator with end ports a D5 pump and bay res should be doable w/o issue
However rather than all this speculation from photos and incomplete review statements, there's a simple and expedient answer to the question since the the OP is looking to fit it in "[his] case". If it's already "his case", using a tape measure to determine the distance from the bottom of the chassis plate w/ the fan openings to the top of the motherboard will answer the question. If he has more than 1.06 inches (1-1/16") he won't have to worry about us speculating whether there is room for the rad.
If he mods the chassis top plate, cutting the necessary holes, the ports / tubes might be an issue by blocking access to important MoBo components ..... and he may lose access to a cable opening in the MoBo tray.
Interesting Note: While looking at pics to try and see how the H100i might fit with regard to the ports, I noticed that the fans as shown in the newegg picture are contrary to Corsair's published installation instructions. The pic shows an exhaust configuration, the installation instructions say intake.