Radiator Stacking

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SUMMARY: Two radiators stacked back-to-back does not give you an overwhelming cooling advantage.

Steve Holbert, one of our readers, had some questions about the cooling performance of some radiators he bought and asked me to test them out. As the pic below shows, Steve sent me two he had purchased; BE Cooling’s twin radiator and two stacked Perma-Cools (Steve had these mounted by a third party). I compared them to two other units: My “Salvage” radiator (I found this at a local scrap metal yard – $10) and BE Cooling’s single unit.


In using a stacked rig, the warm water should enter the rear unit first; this allows cooler water to enter the front unit. If you do the reverse, warm air from the front radiator will wind up further warming the water entering the rear radiator.

All units’ cores are 5 x 5 inches (125mm); the BE Cooling and Perma-Cool’s cores are 1/1/2 inches thick (38mm), the Salvage’s 1 1/4 inches (31mm) and the BE Cooling single at 3/4 inch (19mm). This is a great size for mounting a 120mm fan directly onto the core.


I used my portable test rig; this consists of two stacked peltiers throwing off about 100 watts, a Becket G90 submersible pump and a copper water jacket. Each peltier is separately powered. A single 120mm fan was mounted to each radiator. Each unit was run until temps stabilized and the resulting temp recorded. Results are listed below:



Two Singles

-34.2 C

BE Cooling Double

-33.4 C

Perma-Cool Double

-33.4 C


-33.4 C

BE Cooling Single

-32.6 C

Ambient temp: 23.1 C

Well, surprised me! I would have thought there would be more of a difference between one radiator and the doubles, but this was not the case. I also expected some difference among the doubles, but looks like the same core sizes performed equally; when you think about it, makes sense.

As a further test, I decided to mount two BE Cooling singles with two 120mm fans in series – this is the “Two Singles” entry. This turned in the best results, but not by a wide margin; also very noisy.


Stacking radiators does not give twice the cooling performance; in fact, based on this test, I don’t see where a stacked radiator approaches any reasonable price/performance standard. I would think the best approach would be two radiators in series with two fans – the “Two Singles” test. However, ever this does not justify the expense for a meager 0.8 C gain.

For “moderate” cooling requirements (let’s say about 100 watts), a single radiator will do the job. For extreme cooling, a better approach might be a larger radiator with multiple fans. For best pricing, visit your local scrap metal yard.

Email Joe


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