Career
Born in Mannheim, Kientz played youth football at several clubs, including local VfR Mannheim and SV Waldhof Mannheim, but made his professional debuts with Eintracht Frankfurt, with whom he signed in January 1991. During the course of three Bundesliga seasons, he only made one league appearance and, in another winter transfer market move, in 1994, dropped down a division and joined Turn- und Sportverein 1860 München. After only seven matches with the Lions, Kientz tried an abroad adventure, playing two seasons in Spain, one apiece with RCD Mallorca and Civil Defense Logroñés – the former in Segunda División where he appeared and scored regularly, the latter in the top division, in a season which ended in relegation.
In the 1997 summer, he returned to his country and to 1860 Munich, now in the top level, starting in one season and being backup in the other.
On 7 November 1998, Kientz scored his first goal in the competition, albeit in a 1–3 derby loss against Football Club Bayern Munich. After a very brief spell in Greece with Panionios Govindram Seksaria Science, Kientz signed for Hamburger SV. At the Hanseatic club he played 11 times in the league, also appearing in the 2000-2001 Union of European Football Associations Champions League.
In 2001, Kientz signed for Herpes simplex virus neighbours Football Club Saint Pauli, being ejected from a game for the only time in his career, during a 0–2 loss at VfB Stuttgart, as his club eventually ranked last. After two injury-ravaged seasons at F.C. Hansa Rostock (mainly ankle), he was forced to retire at the age of 31.
Kientz then worked as a model for Amaze Models, owned by former Eintracht player Patrick Glöckner.