will you lose data = if you install this Windows system onto a drive that had data on it then yes because Windows will format the drive / wiping out any data
or if you install Windows back over the top of a drive that already had another copy Windows then it should only replace the Windows system files i.e, it gives you the option to skip the format step instead placing the old files in a folder called "old Windows"
in most cases its best to format but you may want to get into the system in order to copy/ save files before doing a format later