Undiluted hGH powder has been shown to retain full potency for up to 18 months when stored at normal room temperatures.
However, it is recommended to refrigerate hGH if room tempter would exceed 80 degrees F. for a lengthy period of time.
I've alway stored mine in the fridge, and would also recommend to do so... but the statements above come from Dr Cranton
so I would feel safe to say you have a very long shelf life before cooling it.
I should also mention... you should not free it.