Just replaced my 18 Year old WF with a new TE-30 using open loop. Question about Delta T for this setup. I always thought Delta T was computed using EWT-LWT. Is this correct or is it LT1-LT2? The reason I ask is that in the manual it states that water temperature change should be 18-24 for cooling and 10-17 for heating. This particular unit has an automatic modulating valve installed and it can be configured for Delta T or a fixed percentage of flow. When attempting to set the Delta T for each mode it allows a maximum of 20 degrees for cooling and 12 for heating. It just seems to me that it should allow the maximum of 24 for cooling and 17 for heating if that is the acceptable range. When the unit was installed it was set for 7 heating and 12 cooling. I have a minimum LWT of 70 degrees set. So, when operating using the Delta T of 20 the modulating valve overshoots the the temp ranges and then knee jerks the other direction over shooting again. Example using a Delta T of 20 in cooling with a 77 degrees room temp and 74 setting: Starting: EWT 54 LWT 66 Valve 94% 1 minute later: EWT 54 LWT 71 Valve 71% 1 Minute later: EWT 54 LWT 78 Valve 53% This process then reverses with the valve opening back up to the 90% range and LWT falling back to 66-67. When the Delta T settings were set to 12 for cooling the modulating valve appeared to be more stable staying in a tighter range.