1995 Ford Explorer Heater coil problems

I have an internal water leak that releases water and antifreeze out of a sidewall spout. The water is being released from what appears to be a safety spout at the front end of the dash on the inside of the engine compartment. The leak was slow at first but now has gotten to be so bad that the truck is not safe to drive. I believe that the heating coil needs to be replaced. Does this seem to be the problem? Is it something that a novice can replace on his own? What problems can I expect if I attempt this repair?

Should I leave it up to the professionals? If so, how much can I expect to pay for such repairs.

Thanks.