Answer: 87.3 inches
Step-by-step explanation: The height of the pyramid is the hypotenuse of a right triangle whose legs are the height and half the length of the base.
Let h be the height of the pyramid, then:
h^2 + (21.6/2)^2 = 88.6^2
h^2 + 233.28 = 7857.96
h^2 = 7624.68
h = 87.3 inches (rounded to one decimal place)
Therefore, the height of the stainless steel patio heater is approximately 87.3 inches.