Can I put a P3, let's say, on the bottom shelf of my audio rack?  Will it overheat?

May not matter in your case...but I ruled out a P3 because I needed to tone down voltage here as well as wanting power filtering. With the P3, the main, higher power outlet is filtered only, no regeneration. The rest of the outlets are regenerated, so voltage controllable.

Being completely regenerated, I went with an open box P5. As it has turned out, voltage adjustment has been more useful than just regulating it down. As a tuning tool, you can change the sound of your Decware amps with voltage. Notch it up a bit and the sound is denser and more powerful...down a bit and it is more open.

Ok, yesterday or maybe earlier, someone had posed a question about what to buy for power regeneration.  I can't find the post so I'm commenting here.  If Power "Regeneration" is really needed, the PS Audio products are well liked here and receive good reviews but if "Conditioning" is what's required, I would suggest looking into the Running Springs Audio line of conditioners.  I have a "Jaco" in my main system and a "Haley" in my second system.  This brand was recommended to me by a fellow site member who was very helpful when I was getting started several years ago, Mike B. from Seattle, Washington.  I did a lot of reading about these conditioners and can say I'm very pleased with my purchases.  As with much of my gear, I don't have comparisons to other products because I came back to "Hi Fi" after being out of it for many years....the last gear I'd bought was from the 80's and early 90's.  Anyway, if considering Power Conditioning, you owe it to yourself to read about Running Springs history and wonderful products.  Mark.

PS...If you intend to buy on the used market, I would suggest you get one with the carbon face.  Not because of cosmetics but because an internal upgrade was also made with this cosmetic change.  I bought the Haley new when I missed buying a used one from an audiogon seller.  He offered to sell me one direct from the factory for a little more.  The Jaco I got for $1400 with a Mongoose Power Cord...there are great deals for those who are patient.