In Diablo 4, the main lairs to farm for pyromancy-related items are the boss lairs that match the material you need , especially Varshan, Grigoire, Lord Zir, and The Beast in the Ice. The most efficient farm depends on which pyromancy item or crafting material you’re targeting, but boss lair rotations and Helltide / Nightmare Dungeon loops are the core path.

Best lairs to target

  • Varshan for Malignant Hearts, usually farmed through Tree of Whispers activities.
  • Grigoire for Living Steel, usually farmed in Helltides.
  • Lord Zir for Exquisite Blood, usually farmed by killing Blood Maiden in Helltides.
  • The Beast in the Ice for Distilled Fear, usually farmed through Nightmare Dungeons.

If you mean actual fire-themed loot

If by “pyromancy items” you mean fire-oriented uniques, affixes, or build pieces, the fastest route is still boss lair farming because each lair has its own unique loot table and higher-tier bosses can feed into better drops. Torment difficulty is where these farms really become worthwhile.

Practical farm order

  1. Farm Helltides for Living Steel and Exquisite Blood.
  1. Run Nightmare Dungeons for Distilled Fear.
  1. Do Tree of Whispers objectives for Malignant Hearts.
  1. Use those materials to open the matching boss lairs and repeat.

Useful note

Seasonal Journey chests can also give a lot of boss lair key materials, so they’re worth doing alongside the usual farm loop.

TL;DR: if you want the best lairs to farm, focus on Varshan, Grigoire, Lord Zir, and The Beast in the Ice , with Helltides, Whispers, and Nightmare Dungeons feeding the key materials.