I think if performance is important as well as silence and cheapness isn't too big of a factor, I'd go with the
Eheim 1250 over the 1048 as it's considerably more powerful. If you don't want something that powerful, still try to stick with Eheim because they are the quietest of all the pump brands (the old Swiftech MCP600 might be on par, the MCP650 is not).
A
double heater core is generally the most popular way to go and also least expensive, HOWEVER, the esteemed Mr. Bill Adams has shown that for quiet systems, ie, low rpm/undervolted fans, thinner radiators are the way to go. Heatercores require higher pressure fans to get good performance because they are thicker and have a higher density fin arrangement and in general, high pressure means high rpm, and consequently, high noise levels. For a quiet setup, thin radiators are the way to go.
Case in point, the
Swiftech 676. Oddly, Sidewinder has it for less than Swiftech's own store. But then again, the Hydrx water additive, Coolsleeves (prevents kinks) and the Bleed/Fill kit are less and you save on shiping if you get 'em from Swiftech's store. The 676 comes with mounting brackets and quick connect hose adapters so it's really not a bad deal at all.
As for the block, you have two options in my eyes. The Swiftech MCW6000 because it's only $40, (because the RBX and TDX are $52, use poly tops that may crack down the road and don't offer measurably better performance) or option two, the Dtek WhiteWater, which is basically the same as Cathar's original WhiteWater (I think there might be the very slightest difference in peformance), but measurably better than the MCW6000 (1-2C optimal).
As for fans, I can't recommend any other than Sanyo Denki's after using them myself. You hardly hear the motor at all, only airflow. Well, maybe some low frequency stuff, no high pitched sounds though. And they so solidly built too. Best fans I've ever owned. Undervolted they're near silent.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=3673&item=6708287662&rd=1
Don't worry about it ending soon. That seller always has at least 1 listing on ebay for those exact fans. As soon as the auction ends it's relisted. They're a wholesaler of sorts. Great prices too.
So to sum up, the best quiet but good performance setup I can think of would be the following:
Swiftech MCW6000 or Dtek WhiteWater (Danger Den's popularity is unwarranted)
Eheim 1250 (flow rate is THE most important thing if you don't have high rpm fans) or Eheim 1048 (the 1250 is only $10 more and significantly more powerful)
Swiftech 676 rad (cheap and your best bet for quiet fans) or 2x120 heatercore (actually a bit more expensive if you don't buy one from Autozone and make your own shroud)
120mm Sanyo Denki's (102cfm, 39dba, 9.6mmH20 - very quiet undervolted)
And you'll obviously want to stick with 1/2" ID for everything, and use nylon fittings. There's no reason for brass fittings. They'll only break your plastic stuff. And while Tygon is good tubing, it's overrated. Mine still kinks so you're best off saving money and getting Clearflex and using Coolsleeves on it to keep it from kinking. And that's it.
And of course use distilled water and either 15% antifreeze or some other additive like Hydrx (it's green, but it's the only one that doesn't stain your lines or leave deposits on your pump and waterblock). But you already know that.
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