Description
The same dark vulcanite as the AC3040 in the larger 4–6 in fraction — the one to use when a heater has a deep basket or a wood-burning stove needs mass rather than surface area.
Bigger stones hold heat longer and stack with wider air channels, which suits long sessions and stoves that are fired hard. Many builds mix fractions on purpose: larger stones low in the basket, smaller ones on top where the water lands.
Natural stone — shapes vary. Order a spare box if you are filling a large heater, so you can sort for fit instead of forcing pieces into place.
