does amp draw alot of power when volume is zero

If it is an AB amp, probably not much; if it is a Class A amp or biased well into Class A it will draw the full amount of current or a substantial portion of it. This is easy to tell, just feel the heat sinks when it has been on but not playing music, if they are cool or lukewarm leave it on all the time. If you burn your finger don't leave it on. Most amps draw a minimal amount of current and sound better left on.

Stanwal is right. My Krells act like frying pans even in standby.

If you are worried about wasting energy, and money, on idle music systems you should consider Class D amplifiers. These amplifiers are very efficient in use and at idle. My desktop integrated amplifier draws 15 watts at idle and sounds great.

Agree the best simple way to know if your stuff wastes power at idle is the see how much heat it puts out when idling. Nearly all the electricity used at idle is going into heat. The warmer the stuff is at idle, the more electricity you are using at idle.
My prior amp (forte 4a) was a small furnace at idle, and was just as hot idling all day as it was playing hard all day, Class "A".
My current amp, a Bryston 4B-SST2 has more surface and less apparent heat output per square inch, but it is much bigger and twice as heavy as the Forte.. so it is hard to say if it is more efficient?

For those who are actually curious, spend the 25$ on a 'kill a watt' power meter.

This meter will not only give you line voltage, but current, watts, VA AND therefore powerfactor.

A cheap test and part of my standard kit, though never left in system for long.

http://www.p3international.com/products/special/P4400/P4400-CE.html