Are there any issues if I put my Receiver, PS3 and cable box one on top another without shelves? Heating issues?

That's probably asking for trouble.

How much space should there be between units?

I think you'd want to leave at least 3 inches of space between each component. Even then, since receivers and cable boxes (I'm not familiar with the PS3) radiate their heat upwards, a shelf in between each component is the better way to go...

I was going to say what eljay said.

If each unit is on a shelf then the heat from the unit below will, for the most part, not impact the unit above it. This assumes that these are in an open cabinet.

eljay, would there need to be 3 inches between components if there is shelving?

If you read the manual for your receiver, you will find the spec for the top clearance that the manufacturer suggests. My Pioneers are 6", I believe.

DON'T stack all those things up. They are all significant heat sources.

eljay, would there need to be 3 inches between components if there is shelving?As long as the cabinet is properly ventilated - that is, either open (as jvincent mentioned) or closed but with some sort of a small cooling fan to draw out the warm air - you could probably get away with as little as 1" of clearance between a component and the shelf above it.

Heating issues and weight issues too. These components are not meant to support weight.

NEVER EVER EVER stack on top of a reciver. Amps create heat.

Cable box not asd much but if its a PVR the drive crates more heat.

PS3 exhaists out the back I think but since the top is curved I can only assume one would not stack on top of it.

Shelves would be best. If you absolutley won't do shelves then at least some thick spacers to give more clearance would a bare minimum.

BTW PS3 can be stood on its side so depending on space you could stack it beside the other two

Does anyone know if there is a fan "box" you can buy. What i'm pictureing is something i can put on top of my receiver which sucks out the air and blows it out the back (the area behind m components is open)

Here is a link to cooling fans (http://www.middleatlantic.com/rackac/cooling/qcool.htm#compcool) I know that there are other companies that make them but this one came to mind right away. Not sure as to what the price would be but contact your local dealer and they would be able to tell you.

You could also just get a cheap PC fan and wire it up to a 6 or 9V DC power supply - you likely have dozens of old AC-DC power supply bricks that aren't needed anymore - like the charger for your 2001 Nokia cell phone. And you can get quiet PC fans for around $10-15.

They problem with purchasing a PC fan is that it won't push the air out, only up into the next device, if you are going to do that it would be easier on the equipment to just leave the proper spacing rather than introducing more heat onto the next box