Can I daisy-chain extension cords for a space heater?

No. Daisy-chaining two 100-foot cords creates 200 feet of wire, causing voltage drop that makes the heater draw more current and overheat the cords. Even if each cord is rated for 15 amps, the combined resistance and poor connections add serious fire risk. Use a single 200-foot, 12-gauge or thicker outdoor-rated cord instead, or move the heater closer.