Recent threads about DSH operations have prompted me to look more closely at my graphs, and I've found an interesting recurring issue. The four day graph (attached) shows a consistent daily pattern: the DSH produces a steady supply of increasingly hot water to the buffer tank during late evening (9pm-2am) when the 4T heat pump is running constantly to cool the MBR (note 9pm arrows marked on graph). During these periods the buffer tank reaches 105 to 120F -- not as high as I expected from the sales pitch. However, the DSH does not appear to be producing any additional hot water during normal HP cycling. Note the red boxes that show the DSH supply water temperature (black line) does not affect the warmer buffer tank temperature (green line) for typically five hours of heat pump cycling. I assume this is because the DSH water temperature is lower than the buffer tank, in which case this is normal and proper operation. This will be of interest to those expecting to get free hot water whenever the HP is running. Not so! Note the black boxes that show buffer tank temperature (green line) holding or in some cases FALLING while the HP is cycling during nighttime hours (when there is no hot water being drawn). This indicates to me that the DSH is pulling hot water out of the buffer tank. I would consider this to be a problem. Is there another explanation? The second attached graph shows typical HP cycle times. Note: only the 4T (blue line) has a DSH option.