How hot is hot when moving from class a/b to to a or tubes?

I am considering moving from a class a/b Luxman L509x to a class a or tube amp. 
I have never owned a class a or tube amp, so have no experience of living with one. My kids are hopefully old enough and wise enough not to burn themselves, but I do live in an already warm house with bifold doors leading to a south facing garden. There is no escaping the sun, despite having uv treated glass. 
My room is roughly 9 meters by 12 open planed living space. Equipment is, Luxman L-509x integrated, Zu union 6 supreme, 99db sensitivity (this is why I am considering a lower powered tube I can barely turn the Luxman up) music is played roughly 6 hours a day, more on weekends  

who here has moved from class a/b and d to class a with or without tubes. What were the differences of things like:

warming up time 

additional heat to the home

Running in summer time 

additional cost to run

any considerations I should make before purchasing something. I will try in my home, but will need to free up funds 




You are quite right about TRUE Class A. It does run hottest on no/low signals.

Some here have mentioned modern Krells, by which I mean post around 1990.  These do not run particularly hot on no/low signals.  How can this be?  it is because they are not TRUE Class A, whatever Krell may claim.  They run in Class B and have so-called anticipator circuits which sense an increased signal coming in and re-bias the amp to Class A and allow it to morph back to Class B when the volume has died down.

I have never discovered any scientific basis for the claim that this re-biasing can occur so quickly after detecting the increased signal that it can power the sound of that signal.  It seems impossible since the cable runs in the amp are relatively short and the signal is travelling in them at close to the speed of light.  A myth put about by Krell so they could play in Green Park while still claiming to produce Class A amps.  Yes they will exhibit patents but anyone can get a patent.  The issue is: is  the move to Class A completed before the detected incoming signal is amplified?  The patent makes no claim that it is.

No guys.  A TRUE PURE Class A amp like my pair of late 1980s Krell KRS200s, uprated by Krell to 400w per channel runs HOT.  And as Jason says, there aren't many of them.

I can feel the heat from my First Watt class A amp from about a foot away. It runs much hotter than my 300b tube amp. I can tell the difference in room temperature when the FW has been on for a while. 

My Mark Levinson 20.6 class A mono blocks pull 400 watts at idle and run 10x hotter than my Marantz 5 tube mono blocks.  I would swear there is a fan in the amps blowing heat.  I also noticed my electric bill goes up  $100 a month to run the 20.6's.  They are the best SS class A amps that I have ever heard.

Heat definitely varies from person to person and I think room size and location in the world play a huge role in understanding anecdotal information . I have an upstairs south facing room that gets sun for the entire day, I'm located in California, and is only 9x13 and is on the opposite side of the house as my AC thermostat. For me, a class A tube amp and a class A/B BHK250 got my room way too hot to be comfortable during the summer time. I'll be trying out class D next. My font end is all tube and surely didn't help either amp. We will see.