Hot water

Question:

Why is it that, when you turn on the hot water in most hotels, you don’t have to wait for the water to warm up like you do at home? That is, why is the water that comes out of the faucet instantly hot?

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C

A

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A

I

N

I

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E

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I

E

W

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Solution: The interviewer really doesn’t care if you know the engineering that makes this little miracle possible. Rather, the interviewer is looking for you to make analogies, brainstorm, reach for metaphors, and articulate a reasonable conclusion. The answer doesn’t have to be technically correct, just reasonable or reasonably creative. One candidate responded:

Let’s see. In my apartment building, I have to let the hot water run a few minutes before it gets warm. That’s because the water heater is a long way from the hot-water taps and the water in the pipes cools down when no water is flowing. Let me brainstorm a couple of reasons why hot-water faucets in hotels instantly dispense hot water. One is that the pipes are heated. Another is that each bath-room has an on-demand water heater.

By this point, most interviewers would be quite satisfied and ready to move on. These responses are totally acceptable even though they happen to be wrong. No matter. Unless you are applying for a job in hotel plant maintenance, the interviewer doesn’t care. The candidate has demonstrated a fluency of thinking, creative responses grounded in an understanding of elementary physics, and the capacity to analogize new solutions from familiar experiences. One word of caution: If you tell the interviewer that you are going to brainstorm, do so and avoid evaluating the suggestions.

If you knew or could reason out the correct answer, so much the better. Here’s the real reason: Hotels feature a hot-water recirculating system. This system consists of a pump attached to an extra water line that connects the farthest hot-water tap directly to the hot-water heater. The pump slowly circulates hot water through the hot-water lines so that there is never standing water that cools down. Thus when you turn on the hot water, the line water is already warmed up.

Answer: Hotels exploit a hot-water recirculating system.

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