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Need some help optimizing fuel consumption of my Vitodens 100 boiler

satwarsatwar Posts: 24Member
I have a Vitodens 100 boiler with a low loss header and VT2218 delta-T circulator feeding old gravity piping with cast iron radiators. My problem is that installer used default settings for boiler outdoor reset heating curve and 20 F delta-T setpoint for circulator. The system gets hot very fast (180 F boiler water @ 14 F outdoor temperature).

In an effort to improve fuel efficiency, I decided to take a less aggressive approach and try a heating curve making 150 F boiler water @ 4 F outdoor temperature (average winter minimum temperature is 4 F in my area). This leaves some room to handle colder weather down to -26 F @ 180 F boiler water (extreme minimum winter temperature for my area is -40 F)

The other trick is to get the circulator pumping faster with the winter weather. I intially was hoping to use a delta-T setpoint of 35 F on the circulator to minimise boiler return water temperature, but I'm afraid that it would slow the pump down too much and for too long and won't give me the heat flow I need to heat the house. I took a cue from the measured delta-T always settling down to 15 F by the end of a heating cycle. So far, in warm weather, the delta-T setting of 15 F on the ciculator gives a very smooth operation with the circulator in control of delta-T at all times. I tried running the circulator with a delta-T setting of 20 F, but the boiler and circulator started making wild swings during the early stages of the heating cycle and during the later part of the heating cycle lost control as the delta-T dropped below the setpoint and the circulator was already operating at minimum speed.

Hope this makes some sense, as hydronics is not my field of expertise.


  • Paul PolletsPaul Pollets Posts: 3,169Member
    The Vitodens 100 has a simple dial for settings. There is no internal access to multiple coding options that the V200 has. It also has a thermostat TT connection and does not accept the Vitotrol controls. Your choices are limited to a smart circulator and the dial settings.
  • satwarsatwar Posts: 24Member
    Yes indeed, those are the two variables that I have to work with. Unfortunately Viessmann only offered the Vitodens 100 in Canada several years ago when I needed a new furnace. There's no question that it can heat the house, but I don't like the way the boiler gets so hot (+150 F) even though it's only 32 F outside. I can keep the house warm with 110 F boiler water while running the VT2218 at the lowest speed. It seems like there's some room for improvement, even if my options are limited.
  • Paul PolletsPaul Pollets Posts: 3,169Member
    You're limited to the heat dial to control the reset curve. Don't know why you weren't able to get a Vitodens 200 in Canada, they've been available for over 15 years in N. America.
  • satwarsatwar Posts: 24Member
    I specifically asked the regional sales representative and that's what he told me, and there was no room for discussion.
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