Don't know. I guess I'll find out. Surely not enough to make much of a dent on a 15 gallon tank. I'm not too worried about a warmer gas tank. If the temperature of the fuel is under 200 degrees at the fuel rail and a tiny bit is making its way down 10 feet of line to a 15 gallon tank, I don't think I have much to worry about. The fuel lines are exposed to the open air as it is and most of my driving is on the highway, so I would imagine that it would cool tremendously.
There was a guy that did testing with this <heating fuel>, I think it might have been the Hydrogen Boost guy.
One of the reasons for heating fuel with the HydrogenBoost 'system' was to cause expansion of the fuel in the tank resulting in a lower apparent consumption rate since the fuel gauge needle would drop more slowly.
Yet one more reason why I think the whole HydrogenBoost premise is a scam.