In Heat Map, the consumption of the selected source is presented as a “heat” intensity map, with higher consumption shifting towards dark red and lower consumption shifting towards beige.

You can identify site's monthly peak hours, by looking at the dark red areas, usually on working days and on the busiest time of day on some specific days of the month.

In the Heat Map view, the data is shown per hour across the last 28 days. You can change the date to show a different set of days. 

You can also hover a cell to show the consumption for that hour and the scale will pinpoint where that datapoint falls on the scale for more clarity, as illustrated in the next image.

You can click on the High or Low bar and drag it to shift the range and isolate which hours fall in that smaller range.