Assuming you are talking about 16:9 HDTV , the optimal viewing distance is generally considered to be about 3.3 screen heights.
So, if you are 14 feet away, that gives a height of 51 inches. As it happens, the diagonal of a 16:9 set is very close to twice the height, so you would need a 102 inch set !!!
But since HDTV sets and broadcasts are less than optimal at the current time, a somewhat smaller set would be ok.
STOP DVI/HDCP; Boycott JVC