Can you put a Krell in an apartment?

No, you cannot run this amp in your apartment. Take it from one who has had both the FPB 300cx AND the 400cx. I ran my 300cx in a condo and CONSTANTLY was blowing circuits. The 400cx actually has TWO power supplies and absolutely requires a dedicated 20 amp circuit. Given your space, you will absolutely fine with a 300cx and it will sound great. 

There's no big deal about 20 amp. It's used often, especially in kitchens.

In terms of size and weight why would you even want this in a small apartment especially if at some point you want to change things around?
I honestly wish I had the space for something like this but you might see it turn into a major headache physically in spite of it sounding good.

What is the size and weight? It looks like a beast though I bet it sounds great.

I run my Krell 300c on a 15 amp circuit and have never popped a breaker 

Quite a lot of nonsense responses here. I suppose a little knowledge is dangerous. As has been alluded to, there should be no problem running the Krell. Regardless of not using all it's available power, the larger Krells sound better than the smaller ones and this alone can justify the purchase. 
As for the 300 watts at idle, this is common in high-end. Most amps draw between 100 to 200 watts at idle with some extremes running to 1200 to 1500 watts. The suggestion that you need to have strong A.C. because of the 300 watt idle is just audiophile lore. If you have a ton of gear, already you have hundreds of watts at idle, the Krell is not going to add that much more. Additionally I have found that you don't need to have the Krell on all the time at any rate. An hour or two turn on before listening will suffice to stabilize the sound quality. Enjoy!