Primary loop excess flow=low ΔT

Larry (from OSHA)

My Knight 80 is working great, but of course I’d like to get the most out of it. I have 3 zones of baseboard with zone valves driven by a 15-58 on speed 1. I believe the system design is 20° ΔT and has been running about 10° at this time of the season.

The boiler loop is something else though. With all three zones calling, there is less than 10° rise across the HX and the inlet temp is about 10 degrees or so above the system return. With only 1 zone calling, the rise across the HX is only about 2 to 3 degrees.

The boiler pump is a 26-99 on speed 2. Currently, I need to run on speed 2 to make the flow switch which is a McDonnell Miller FS-4.

It seems to me that reducing the boiler flow would result in a wider ΔT and lower return temps at the boiler inlet. Of course, I don’t want to reduce the flow to less than what the factory wants, but with the numbers that I am getting now, I’m thinking that there might be some room to move. I have tried the boiler pump on speed 1 with the flow switch jumped out and there was only a little improvement, but not enough. I would think that a 15-58 on the boiler loop would put the boiler and system flows in better alignment, but I’d really appreciate some perspectives.

Larry