Wood-stove/Fireplace mounted water boiler

Essentially, this would be a small tank(about 2 gallons) that would be setup on the same tile as a fireplace or wood stove, and when filled, and a fire is going, will boil/purify any water placed into it. this would prevent you having to keep manually boiling water and would only require you to fill the tank with regular water. any time you lit the fire for other reason the water would be automatically boiled at the same speed as manually boiling it.