The ornamental design for a biomassstove, as shown and described.
FIG. 1 is a front isometric view of a biomass stove.
FIG. 2 is a front elevation view of the biomass stove of FIG. 1.
FIG. 3 is a rear elevation view of the biomass stove of FIG. 1.
FIG. 4 is a left side elevation view of the biomass stove of FIG. 1.
FIG. 5 is a right side elevation view of the biomass stove of FIG. 1.
FIG. 6 is a top plan view of the biomass stove of FIG. 1; and,
FIG. 7 is a bottom plan view of the biomass stove of FIG. 1.
The broken lines, which depict unclaimed portions of the article, form no part of the claimed design. The broken lines that border claimed portions of the article are boundaries of the claim.