There is no way to measure the temperature of the components (they don't have built-in thermometers like CPUs). However, it is a very sound assumption that companies like Denon (or Marantz, Yamaha, etc) which have been designing electronics and their cooling systems for decades, know how to use a heat sink. As long as we can pull fresh cool air through the unit on a steady basis, you are optimizing conditions for cooling.\nThe rate of heat transfer into the heat sink is directly proportional to delta T (the difference in temperature between the hot component and the heat sink) so as long as we keep room temperature air flowing across the cooling fins, we are in good shape. Understand this is a unit designed to work many years from natural convection (just the heat rising), so increased air flow is going to make a substantial difference.\nI should also comment (while on the subject) that these units come with built-in fans, but by all accounts these fan almost never come on. The belief is these fans are purely for testing so when someone (does FCC still test?) sees what the max continuous wattage the unit can put out, the fan will kick on, rather than getting a thermal shut-off. This is another example of how effective a fan is because the unit gets very hot before these kick on, but they have no problem "catching up" with the high temperatures.\nFrom the standpoint of maintaining long term cooler temperatures for reliability, the $20 fans are the way to go. They also make some low clearance boxed-in fans that exhaust to the front or to the back if you have a (too) close shelf above your AVR.\n\nI feel it's a good idea to use cheap fans.\n\nBut at the same time, there is no PROOF that using fans will increase reliability.\n\nUsing 3 x 120 mm fans atop my AVP-A1HDCI did not make it last longer than ~ 8 years. Grassy's AVP-A1HDCI also died about 8 years, and he never mentioned using any fans. Of course, this is not conclusive and is just theory.\n\nWhat if using fans increase the air flow and also DUST to accumulate INSIDE the chassis? The fans themselves, while pulling air\/heat out, also physically block some ventilations in the chassis. The reason I mentioned dust is because I noticed MORE DUST on the fans themselves than on the chassis areas that did not have fans.\n\nMy conclusion is that if your AVR heats up like crazy, then definitely use fans. I think heat is a lot worse than dust. But if it does not heat up like crazy, then don't use fans because you don't have proof either way.