Hearthstone

These flat, round or ovoid stones of Ignium are cut perfectly to fit into fireplaces or under a mattress, keeping chambers warm in the coldest winter. One hearthstone keeps a 20-foot-square area comfortably warm even in extreme cold (below –20° F), or a 40-foot-square area in severe cold (between 0° F and –20° F). The stone is activated by command word, after which point it continues to provide heat for 12 hours and renews after 12 hours. An active hearthstone does not give off enough heat to cook food or cause damage as the heat has no flame. Widely popular for those who don't like the smell of smoke.