This is how much hot water hotels ACTUALLY Needed in 2023 (by number of rooms)

How does one design a system that is large enough to meet any and all anticipated loads yet small enough to be space-saving and energy efficient? With a data-backed approach.

The graph above indicates the average amount of hot water (in GPM) that hotels across North America need, broken down by the number of rooms that they have. What stands out?

If you are an engineer, you must be familiar with the issue of sizing a large property’s hot water needs. The proposed hot water system needs to meet large hot water demands, while being economically and spatially viable. “What if all 100 rooms start their showers in the morning at the same time?” is a common question you may have been faced with.

This is not a catch-22 situation. We’ve collected, analyzed, and visualized hot water usage patterns from hundreds of commercial properties to tackle this fear with statistical confidence.

About the Data:

The graph above has been visualized using data from our online sizing calculator from January 1st to December 13th, 2023. The data consists of information collected from 1710 hotel properties across North America. The information collected includes the number of rooms, hot water fixture counts and types, as well as the incoming and desired outlet temperatures.

Where do the GPM estimations come from?

The GPM estimations are a result of the “theory of diversity”, design guidelines from ASHRAE and the Uniform Plumbing Code, as well as a review of existing sizing methodologies.

The theory of diversity is really a theory of probability regarding how many fixtures will get turned on simultaneously. Intuitively, it is apparent that buildings don’t operate with 100% fixtures open at the same time.

So, how do we logically design a system that is large enough to meet any and all anticipated loads yet small enough to be energy efficient and space-saving? Utilizing these field measurements from various applications across the United States and Canada, our sizing calculator models GPM estimations with a safety factor. Let’s look at an example:

320 Room Hotel in the United States' Midwest Region

This 320-room hotel in Southern United States features 3 full-service restaurants and a commercial laundry. It was originally served by two boilers with an output of 3 million BTUs/hr. The measured peak flow in case of peak occupancy was estimated to be 56 GPM, which resulted in a diversity/probability ratio of 11.7%.

8 Intellihot wall-hung units now service this location reliably, reducing the heating output (and energy expenses) by more than 33%.

What this means for sizing commercial properties:

Our data and experience installing commercial water heaters in large hotels (find our case studies here) confirms that a shift in mindset regarding hot water sizing will benefit engineers as well as property owners.

When a large hotel has 100 rooms, does a hot water system need to have enough hot water for 100 showers ready at all times? Not really.

Although unlikely, if 100 hot showers are turned on at the same time, a tankless water heating system needs to only deliver enough hot water that is needed for 100 showers instantaneously. That is, it only needs to deliver enough hot water that the 100 showers demand per minute/per second.

A tankless system will never need to deliver the composite total of hot water consumed by 100 full showers at the same time. Here is a video addressing the common fear of sizing a commercial property for its worst case scenario: 

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Commercial Hot Water Design

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"We are very happy with our Intellihot hot water system. Over the past six months, the hotel has had 65% gas savings plus uninterrupted hot water."

Download the Engineer's Guide to Commercial Hot Water Design

With Real-World Dos & Don'ts