In 1957 Fortune magazine detailed how aerial photographs of Philadelphia were used to determine the spread of air conditioning. Almost 5,000 homes were mapped and plotted in several neighborhoods to uncover purchasing patterns. Results revealed one block of homes might contain 15 units while the next block had only one or two. The survey drew two interesting conclusions: Dense air conditioning clusters resulted when neighbors talked about their new air conditioner and the people who installed it; without word-of-mouth referrals air conditioning ownership was uneven or nonexistent.

If our HVAC pioneers had a planned referral process in place, air conditioning use and distribution would have skyrocketed. Key elements of a planned referral process are: