Top mounted rads, intake vs exhaust and the temperature differences

3t3P · 9 Sep 2010 at 12:40

Thinking about this, what is the difference in performance of intaking cool air through a top mounted radiator and exhausting system air through a top mounted radiator?

I can't decide what to do on my 700D, IMO it will look loads better to have fans orientated under the rad grill sucking in air and exhausting out the back 140mm fan.

As against 140mm intaking air and exhausting this out the top.

Both setups would be in push configuration on the rad with shrouds

Will it be like 2-3 degrees difference?

dazzerd · 9 Sep 2010 at 12:46

I used both methods on my 700d and I find that having air being blown into the case with the 140mm at the back and puched out through the rad at the top is by far the best method.

You would think that pullin or pushing fresh air through the top of the case, into the rad and out the back would be the best option but for some reason it just doesn't work as well.

I found this method to be significantly worse then pushing air out and up through the rad by about 5 degrees.

I think it has something to do with the "rad grill" on the 700D being quite restrictive.

MikeTimbers · 9 Sep 2010 at 12:50

Marginal to be honest. The crucial dfference in water-cooling is that much of the in-case generated heat is no longer in the case. It's in the water and hopefully being removed by the radiator/fans. For that reason the in-case air temperature is much lower than in a normal system.

So, the long and short of it is that the external air being sucked in is not much different from the air being pushed out.

BUT, given that you've managed to get all that heat into the water and radiator, why would you want to now put it back into the case?

So, for me, a radiator always uses in-case air which is then expelled outside the case. This keeps the heat outside.

As to looks (personally I look at my monitor not my computer!) why not have the fans under the rad and pushing air through the radiator out the top?

Makhaira · 9 Sep 2010 at 12:51

Hot air is less dense and rises naturally. Don't fight the laws of physics, they will win!

3t3P · 9 Sep 2010 at 12:55

yeh it definately makes sense to exhaust in the upward direction, just I will have to flip the 140mm fan around to be an intake, and it will look a bit gash lol in that orientation.

I have also read that on the 700/800D it is best to intake at the back and exhaust out top. Pusher makes sense here to help that naturally rising air.

We need 'pusher' fans, fans that look normal but spin in reverse to push air out in the opposite direction to normal...

1kiwi · 9 Sep 2010 at 21:15

Makhaira said:
Hot air is less dense and rises naturally. Don't fight the laws of physics, they will win!

This. I have recently switched to my PA120.2 sucking cool air in (push/pull) and my PA120.3 (top rad) sucking air out. I havn't seen any rise in my PA120.3 loop but my 120.2 loop is much cooler. The case is also much cooler overall.

1kiwi · 9 Sep 2010 at 21:16

3t3P said:
I have also read that on the 700/800D it is best to intake at the back and exhaust out top. Pusher makes sense here to help that naturally rising air.

Yep, I have my exhaust at the back, single 120mm fan sucks cool air in.

Bubo · 10 Sep 2010 at 09:00

With the 800/700D I had one idea about the top rad to get the best of both worlds, i.e. venting out through the top grill, but sucking in fresh cool non-case heated air. My idea was to have it mounted case-fans-rad-shroud. The shroud would be modded to block the three fan openings and a duct made to connect one end of it to the case perforations at the back of the case which are otherwise pretty redundant. You could go one step further are dremel out this area to make a bigger air intake, maybe put a filter on it. The empty shroud should give enough clearance from the bottom of the rad to allow air to be sucked in through the air intake and out through the top, thus feeding the rad with non case heated air. This would only work if you are using fans on one side in a pull configuration however.

Another idea was to put some fans in the case side just below the top rad, such that the area is directly blasted with outside air which should then go straight out through the rad. This would add to the noise however.