Whenever I put an exponential height fog actor in my scene and make it volumetric it hurts my frames by 30-50 fps. Is there any way to optimize this or is this not supposed to happen. Please help!
That’s pretty much the case, volumetric fog is heavy on performance but there are a few options within the volume fog parameters to play with to help it out. Usually it will eat up that performance unless there is something else unknown to us that we are both missing.
If I correctly remember activating volumetric fog with default parameters will increase the frame times in extra 2ms (two milliseconds)… not really much depending on the hardware you have… which brings the question: Which is the hardware you are trying to run this?
In most our projects on GTX 1070 - 1060 Volumetric fog significantly slowed down performance sometimes to a crawl, It also probably depends on the amount of objects in the scene and their poly count perhaps and the amount of lights in the scene, but in general in all our cases at least it slowed down to the point that up to 50% of performance was lost so we avoided using it entirely unless perhaps if its in indoor contained spaces with limited objects on screen.
I think that the way to solve the performance hit is to use particle systems and enable it when it is necessary… this works if you have pretty much environment clipping the view, but if you are in an aerial view and want to see the whole scene (even 20Km) with that fog showing up, then nothing can be done 
One little spawn here and there is the way to go.
Based of my experience with Expo Fog, its a hard hit on the GPU and my game is a 60FPS game so the Expo Fog did cause a hard FPS drop but I did find
ways to cheapen it and now its being used with little to no hit on GPU and my 60FPS remains.
Find ways to optimize the GPU in your game that’s one of the best ways to look for a increase in performance.
Thank you all for a reply, I haven’t check this in a while but I did try using a material to place volumetric fog wherever but it ended up looking terrible. I’m never going to understand UE4, everything I do causes my frames to drop to 19 fps even with careful optimization.
I have just made a small tutorial about Volumetric Fog with particles at this thread: https://forums.unrealengine.com/community/community-content-tools-and-tutorials/1573652-interactive-volumetric-fog-swamp-fog-like-effect
It would be interesting to know which is the hardware you are using for us to understand if it applies performance constraints on what you are trying to achieve, then we can also give to you a better advice.
I will definentely check out that tutorial.
My specs:
CPU: AMD Ryzen 7 1700x Eight-Core
GPU: GTX 1080 ti
RAM: 16 GB
Currently I am using a GTX 1080, but I got 32GB RAM, same processor, and I am not having the same frame drop but just putting the Exponential High Fog at the level and turning ON the volumetric effect. I think this is most explained by the level itself being different. You can check using the profiler and also by pressing F5 while running the game to see how your scene is behaving when the volumetric fog is ON. While running you can also turn off the component visibility to evaluate this.
I’ll check that out