The only components which are going to be generating appreciable heat are the output transistors. As noted above, the chassis is designed so that cool air enters at the bottom and is vented through the top, so placing it on its side will defeat this. You can try the side placement and see how hot it gets, and if necessary, use a small fan to force cool the heatsinks, but I think you will be OK if you don't play it extremely loud for extended periods. Amplifiers and receivers usually have a bi-metal thermal cut-out switch attached to the heatsinks to shut the unit down if it gets too hot.