"spent steam"?
I am not running a steam engine in my home. I have a 'single pipe steam radiator' system. In my home the "spent steam" that returns to the boiler is _liquid water_.
When one of these steam generators is used in a shower, steam at atmospheric pressure is pumped into the room.
If the moisture capacity of the air flowing in that room can hold the mass of steam being introduced, then I agree you won't get condensation, just heating.
But I presume that one of the desired effects of having a steam generator is to actually get 'steam' (meaning saturated air with suspended droplets of water). If you have a room where the air itself is already _at_ its dew point, then if the walls are at all colder than the air there will be additional condensation at the walls.
Here is a link to an example steam generator:
Your home spa is where you take residential steam bathing to a new level. A personal steam room elevates bath culture to a higher level of sophistication and satisfaction. With its elegantly designed steam shower systems, the latest word in bathroom remodeling, Mr. Steam introduces a new...
www.homedepot.com
The instruction manual gives sizing based upon the volume of the room, and for a large room you might need a 15 or 20kW unit. Per the instructions, 20kW for 875 cubic feet, which is roughly the size of the room shown in the original post.
20kW boils roughly 62 pounds of water per hour. This is enough water to saturate 16000 cubic feet of air at 110F.
If you have an 875 cubic foot room, and have 19 air changes per hour with bone dry makeup air, and the steam heats the air by mixing without condensing to 110F, then you won't get condensation in the room.
But clearly this unit is sized to _saturate_ a room with a normal level of air exchange. There is going to be condensation all over the place.
-Jon