How is vierzehn meant to be pronounced?
Duden marks it with a German "short i" (as in "Hirte"): https://www.duden.de/rechtschreibung/vierzehn#aussprache
In hyper-correct pronunciation, it might be pronounced with a "long i" as in vier, the way Radioman on Forvo does.
And in casual speech, the vowel may become more or less rounded, perhaps under the influence of the labial f before it, so it might sound like fürzehn with a "short ü" -- the result being similar to the English "fur".
A similar effect occurs with wird, which may sound like würt in casual speech.