Estimating the number of lifts in the US

How many elevators would you guess are installed across the United States? Explain your estimate.

Somewhere around 1 million. Split by building type: tall residential blocks (say $100{,}000$ buildings with an average of $2$–$3$ lifts), office and commercial buildings ($200{,}000$ with $2$ each), hospitals, hotels and malls (tens of thousands with several each), plus low-rise buildings with a single lift for access. Summing gives several hundred thousand to about a million; published industry figures are close to $900{,}000$–$1{,}000{,}000$.