DuroMax portable generators will output an industry standard total harmonic distortion (THD) rating of about 12%-20% depending on load applied. They will produce a sine wave, not a modified or square wave. This is perfectly acceptable for running common commodities found in your home such as TVs, computers, your appliances, etc. THD is a measure of the deviation of a sine wave from a "perfect" sine wave. All electricity, including power company electricity, has measurable THD. If you have a specific item that requires less than 5% THD such as a UPS style battery backup, a pellet stove, or high efficiency furnace control board, we recommend purchasing a DuroMax Inverter Generator that provides a less than 5% THD. Please consult your specific appliance manufacturer to determine if the appliance requires low THD (less than 5%) to operate properly.