Q. If one has many pieces of chometz left, is it better to burn them all, or is it enough to just burn a kezais and the rest he can throw out or flush down?
A. Moadim Uzmanim (3: 194) asserts that one complies with the mitzva of burning chometz only with the last kezais of chometz one has. However, he quotes that the Kehilos Yaakov disagrees with him and maintains that one complies with the mitzva on every kezais one burns.
Horav Shlomo Miller’s Shlit’a opinion is that if it is possible, he may burn as many as he can, as each kezais may be part of a new mitzva.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller Shlit’a