Thirty seconds, until the afterglow light turns off. I have a 1/4 mile gravel driveway so slow driving is required to prevent throwing up clouds of dust. By the time I make it to the highway, the heat is almost ready to come on. Any more warming up is just wasting fuel. Going back into the house while the car warms up is a good way to get your car stolen.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970