Hi,.could placing hub behind my TV set and set top boxes, cause any interference to z wave range capability?
Yup. TVs partially block RF signal. It is more noticeable on 2.4GHz or 5+ GHz signals, but it will reduce strength on MHz level signals too.
How much depends on the TV and geometery of the house/walls. And whether the reduction in signal is impactful/meaningful is application specific too.
Try it. If it works, then it works. 
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