HDR Files are similar sizes between compressed raw and standard raw.

[Eamonn0101]

Hey!
I noticed that when I merge 3* 30mb raw files it creates a 100mb HDR file and when I merge 3*15MP C RAW files it also creates a 100mp HDR file. I'm exporting these as DNG.
Is there any way I can seriously reduce the file size?
Thanks!

[SeanMcCormack]

No. 

I did test out running Convert to DNG using Lossy Compression, but it actually created larger files. 

Assuming you're happy with the process, you could always render the files and get rid of the HDR work fiile. If you have the Raw files, it can be recreated and the settings could be saved as a Preset if space is really that much of an issue. 

[JohanElzenga]

When you merge to HDR, the raw files are demosaiced to linear RGB and then merged. As long as the pixel size is the same, it does not matter if you use compressed raw or standard raw, because both will be converted to the same size linear RGB file.