I'm trying to get a good effect of water vapor in a small square room with a light on each side.

Using "atmosphere" can not seem to get good results, practically can not produce "steam" in the room ....

you have any suggestions?

The atmosphere shader setting shown, from a small collection I've developed based (of course) on something BagginsBill posted years ago -  is one I've called 'mist'; you might want to darken the 'sky' colour of the clouds node to give some differentiation. Note that you can ignore the DepthCue start and end distances because we're not using that, but all my units are in Metres.

The atmosphere strength settings on the light (a spot here) are easy to overdo: 0.025 will give you quite a thick effect, you can drop this to 0.01 or less for a more subtle effect.

NB: do not use the volumetric atmosphere with Infinite Lights! If you need atmosphere for an outside scene, convert an infinite light to a spot, constant attenuation, use angle start / end, distance start / end and intensity to simulate daylight or moonlight. 

Set test renders very small because volumetric atmosphere really slows FireFly down...

In your render settings configure Auxilliary Render Data to include 'Position'. If you save the render as a .PSD there will be a weird looking colour layer sitting above the main render. View each channel separately and it will be apparent which one is Depth (Z), Height (Y) and Left to Right (X). 

I did the atmospheric effects in this image (original below) using combinations of these channels.

If you want commerical (paid) version, search for clouds or fog in the store here or DAZ under environment or props.

If you want free version, search for clouds or fogs in the free stuff section of this site or ShareCg.com

If you want a tutorial on creating fog or clouds, go here

There's another way of doing fog or clouds and that's post work.

Hope this helps.

and the one on render passes, handling fog in post with PPro: http://www.book.artbeeweb.nl/?p=388

above a quick Andy-in-the-Fog (standard fog atmosphere) result from an earlier thread on car headlights.

by the way: I'm not sure IDL is a good idea in foggy atmospheres

Quote - does this look like sauna steam?  is kaposer's freebie pipes room. 

It looks like steam or low level fog... Perhaps less density?

BTW, where can one fine the pipe room?

FYI Poser's volumetric atmosphere is additive - it does not attenuate light behind the fog - it just adds light from the fog. 

While this is a workable hack for a lot of scenarios, realistically it's wrong.

thanks to everybody

just to add, here's one where it's even steamier.  using BB's shaders, IDL, inf lite, raytracing, envsphere as always.