Setting all pixels with value

I am using QGIS.

I have a DEM raster with pixel values between about 3000 and -0.0003.I need to set all pixel with a value of 0 and smaler (<=0) to "nodata" (for later raster calculations and to reduce the filesize).

It seems for me that this is a task for the raster calculator (set value of pixels <=0 to "nodata") or a reclassification (set value of pixels <=0 to "nodata" and keep all other values) but I dont know how.