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

With your speaker’s efficiency you should take a hard look at Valvet Class A amps. They fly under the radar but get universally outstanding reviews and rarely come up for sale but there’s one available now. I’d highly encourage you to check them out. 

https://www.usaudiomart.com/details/649955814-valvet-e2-12-watt-single-ended-solid-state-amplifier/

I’d also mention the Plinius SA103 that is also Class A but includes a very useful low-bias switch that lets the amp run in a much cooler Class A/B mode for less critical listening or if you want to leave the amp on 24/7 so it’s always warmed up and ready to go when you want to do more critical listening in Class A.  Hope this helps, and best of luck. 

My CODA #16 amp with the first 100 watts in Class A and 150 total is just warm not hot. A great sounding amp and the anchor of my future Livingroom system.

My KRELL Duo XD lineup amps, which I sadly sold, were all Class A and ran cooler than the Coda. For, example the Duo 175XD is 175 watts of Class A. It is Class A done like Westminster Labs, using a biasing approach. I was planning on buying the ultimate KRELL amp, the KSA i400, which is 400 watts Class A and runs just warm (another KRELL XD amp). I still may buy it, but I changed course and decided to buy an expensive DAC and use a second-hand CODA #16.

My RAAL VM-1a is a tube-based headphone amp and it runs as hot as a furnace. It sounds incredible and the best amp for the SR1a and CA1a phones.

Though my favorite amps are my Benchmark AHB2 monos and they are Class AB + H and are the coolest running of all my amps. I just wish they were as powerful as the CODA #16 or KRELL. I am listening to RUSH Moving Pictures using the AHB2’s as I type this and damn what a sound.

If you are going Class, A, check out the KRELL XD lineup before spending money on the traditional Class A amps.

BTW - I just read your speakers sensitivity rating. With that speaker do a 30-day home trial of the Benchmark AHB2 amps. It will be great with your gear and cost ONLY around $3K. My CODA #16 is $16K (new) and it is sitting idle in my office while I listen to the AHB2. I always go back to the AHB2.

I have all Audio Research Reference gear… nearly 40 tubes. 140 watts per channel. I just went over and held my hand around one of the power tubes… it was slightly hot… touching it, it felt very warm… maybe hot… but you would have to work to get it to burn you. The preamp has 7 tubes is slightly warm. On top of unit.

I have a large room, never noticed it warming the room… but when it 100+ degrees out my air conditioner is on. It does nothing to warm the room.

I seriously doubt my listening amounts to more than a couple dollars a month. 
 

‘’The design does determine the heat. Some designers use the tubes to their max and will generate more heat and shorter tube life. My tube life is over 3,000 hours per set.

To me this is completely a non-issue compared with the incredible sound quality you get with a great tube amp.

@mpoll1 

Another thought might be to get a tube preamp and a SS class A amplifier or two.  The tubes in the preamp can last 10,000+ hours and throw off a lot less heat.  You can get the tube sound without the fuss and expense of output tubes. Also many companies are making hybrid amps that have driver tubes, solid state output.  I have a couple of amps that are exactly opposite of that.  They have solid state drivers and tubes for the output.

All the best.

Its all relative. For sure SS Class A runs hotter than A/B. Digital amps run cooler. Tube amps run usually hotter than all three, except perhaps for ghdprentice, but, for example I run a 40wt tube amp 10 to 12 hours a day. Puts out a bit of heat but really doesn't warm my house much as far as I can tell, nor does my A/C bill run high. The up side is in the winter I keep my house at 68 degrees and if my hands get chilly I just walk over and put them on the transformers, not the tubes!).  My expense is I go thru a quad of tubes every year and that can be a bit pricy, but it was worse when I ran a big tubed amp and it was two quads. The enjoyment I get from music greatly exceeds the small additional costs involved in running the equipment.