Belt of Heartfire Location - Morrowind
Location: Kogoruhn, Charma's Breath
Requirements: Levitate // Method of getting over the ghostfence
Video: How to easily get Belt of Heartfire
Belt of Heartfire is obtained by killing Dagoth Uthol inside of Charma's Breath, one of the areas in Kogoruhn. You will most likely find this enemy while doing The Path of the Incarnate Story Quest since you'll be tasked with coming to this portion of Kogoruhn for the Shadow Shield. However you will also be told to come here during the final quest of the game too, The Citadels of the Sixth House.
Regardless of the quests, you can technically come here at any time and kill Dagoth Uthrol for the Belt of Heartfire. If you enter Kogoruhn via the Charma's Breath entrance, as shown on my map below, you'll be face to face with Dagoth Uthrol. This makes his accessory the easiest Artifact of all the Dagoth's to collect.