How much air does my preamp need?

I'm guessing the manufacturers suggestion is probably a bit of overkill? In this situation I don't have a lot of choice. It's either an inch on top or no stereo in the living room. 

I am a guitar player and have used tube amps for decades. Many guitar tube amps are completely sealed with no ventilation at all and most of the rest have very poor ventilation and yet these amps can be used hard year after year or decade after decade. I've done many gigs outside in the heat of summer with only favorable results. Are stereo amps more susceptible to heat? How many tube preamps actually get 6 inches of space above them in the racks most of us use? What would be the temperature difference in 1-6 inches of clearance on the top? 

I'm not arguing just trying to get to the bottom of this because it is important to me. I do appreciate all of the replies.

If the sides are open it will be fine. I’ve talked to Pass and a couple of others regarding a similar situation I have running class A amps. If the front and back and sides are open, you will have no issues with overheating. A preamp, as mentioned, doesn’t put out much heat.

That's what I suspected but I don't know what I don't know so I thought I had better ask. Thanks geof3 

I have the same problem with my Einstein The tube preamp. I installed a computer fan behind the preamp, and tuned it so it runs without noise. It reduces the heat. But I also - unlike before - turn the preamp off when not in use.

There is not a single component in electronic gear that does not have a set of specifications on useful life that does not show decreasing life as a function of increasing temperature.  I personally would not gamble with running hot. 

At a local shop which only sells tube electronics, I talk a lot to their repair person and MUCH of their service repairs involve overheating, including some wild events like components falling off of the circuit board because it got so hot that the solder melted.  In almost all of the overheating cases, someone put the component in an enclosed space that did not allow for sufficient ventilation.

If you must put it in a place without sufficient clearance on top, you should do as someone suggested above--run at least one computer muffin fan to move the air around the component.  Regardless of the ventilation condition, it is NOT a good idea to leave tube electronics on all of the time--turn it on when one wants to listen; tube gear sounds decent after only a few minutes of warmup.