set cells with specific values as NoData in afloating raster

Seeing as you talk about SetNull I will assume ArcGis. You will need the Spatial Analyst extension to perform this type of extraction.

Your friends in ArcGis are Con and Extract by Attributes, this will allow you to specify a clause on what values you want to keep, anything else will be Null.

For example, if you wanted only the parts of a DEM that are above 0:

The biggest problem is creating an appropriate 'where clause'. For example to extract only a range:

Con is a bit more powerful when used in raster calculator, you can use it to set null values or replace values with a constant (or a different raster):

Will give you a raster that is NoData for less than 215 and the value of the input for values greater than 215.

With both of these tools the output will be the same as the input, so if input is Float 32 then output will also be Float 32.

If you don't have Spatial Analyst you can try the QGIS raster calculator, which is very much like Esri Raster Calculator or GDAL_Calc, both will work if you're prepared to learn how to use them.