Gas water heater draft hoods provide additional air for the combustion process gases, to be properly pulled out from the burner chamber (base of the water heater), into the water heater vent pipe and the chimney.
Mycelium is a block added in Minecraft the same time as the introduction of the Mushroom Biomes in Minecraft 1.9pre1. Mycelium can only be found and only can be found in Mushroom Biomes. Mycelium resembles dirt in that it can be broken with a shovel and it without a 'Silk Touch' enchanted tool it only drops dirt when broken. Mycelium also lets off a small particle effect the same as Bedrock.
A mass of hyphal elements is termed the mycelium (synonymous with mold). Aerial hyphae often produce asexual reproduction propagules termed conidia(synonymous with spores). Relatively large and complex conidia are termed macroconidia while the smaller and more simple conidia are termed microconidia.