hearth, furnace, kiln, reactor
炉 centers on an enclosed structure for containing intense heat: a hearth, furnace, kiln, or reactor. The common thread is a contained space where fire or heat is used for a purpose.
炉 combines 火 (fire) with 户, which is a simplified form of 盧, likely contributing the sound and possibly the idea of a container. The modern form is a phono-semantic compound with a simplified phonetic.
The left side is fire 火, and the right side 户 looks like a door or enclosure. Picture a fire contained behind a door-like opening: a hearth or furnace.
For ロ, imagine a low, roaring fire inside the hearth: low -> ロ, and the flames are contained within the furnace.
hearth; fireplace
fireplace or hearth dug into the ground or floor
fireplace; hearth; stove
nuclear reactor core
smelting furnace; blast furnace
sunken hearth; sunken fireplace
censer; incense burner
fireside; hearth; by the fire
blast furnace
light-water reactor
fireside
CANDU reactor; Candu reactor
crucible furnace
arc furnace
gas cartridge stove; portable stove; camp stove
gas-cooled reactor
gas furnace
coke oven
swimming pool reactor
magnox reactor