A residential pulse-combustion furnace operating on natural gas (NG) spiked with siloxanes has been studied experimentally with the goal of understanding the impact of such impurities on furnace performance. Siloxanes were shown to decompose completely during NG combustion in the furnace to form silica microparticulates. These microparticulates coated the internal components of the furnace, such as the flame sensor, condenser coils, and tailpipes, and they also accumulated in the water that condensed on the furnace's flue vent. The coating of the flame sensor presented the key challenge for furnace operation because, after a certain period of exposure to the siloxanes, it was no longer able to sense the flame, thus causing the furnace to stop operating. In addition, a fraction of the silica particles of submicrometer size became entrained in and escaped through the flue gas exiting the furnace. The results of this investigation point out the critical importance of adequately removing these siloxane impurities from NG prior to its use.