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

Exposed tubes can present lethal voltage, extremely high heat (enough to burn) and should not be around small children or pets. Regular maintenance of these devices, if well made, can lead to lifetime ownership. 6336 tube running at 18 watts per side.

Your questions:

warming up time 

additional heat to the home

Running in summer time 

additional cost to run

are trivial. The way I look at it, your first stop is assessing the quality of the power coming in. Are you in a single family dwelling? You wiring from the city line to the meter, or however it is configured, is usually the city's, but they will check it and can pull the meter. You want a clean, well done layout to your service panel and from corrosion at the meter connections to funky wiring, bad grounds, corrosion or some "hot spot" on the panel, you should have it checked. Then look at how you are feeding the system- dedicated lines? That's a sort of minimum in my estimation. 

The cost of tubes is the tubes. Sourcing them is another matter. 

Additional cost to my electrical bill: have no idea. I'm in Texas, it gets to be 110F here in the summer; there are grid warnings, and I usually don't play the system then, just because the grid is less "stable" for lack of a better word. I installed a 10kva Iso Transformer for the system that outputs 4 gauge to a more local service panel, where 4 20 amp dedicated runs of 10 gauge are installed. It is normally a very quiet system. 

Warm up time- 45 minutes for the amps; 3 sides for the cartridge. 

I use to think my two mono tube amps ran hot. Recently completed a custom full Class A 50w solid state amp build with the help of a local tech.  It runs even hotter.

Hot is hot. We pay a small price and inconvenience for the sound - still think its worth it for the type of sound it yields. When it warms up faster, even better! :)

My Pass Labs XA30.8 Class A amp runs cooler than the tubed Rogue ST100 that I had before it.

I can hold my hand on the heatsink and it’s not terrible. It’s also not too bad in the summer.

As to the warm up time, both the tubed Rogue and the SS Pass need about an hour but the change is not drastic. 

Where to even begin…. All of your responses have been really helpful. Massively appreciate the time taken and passion for the subject. 
 

I have take all your suggestions and will start my research for my new purchase. 
 

Thanks again.