Vitodens 100w B1HA - 82f Heating Curve Setpoint

Mbt93

I moved on an older 1907 home last March. It has a Vitodens 100w B1HA 94 W/ Outdoor Reset. Baseboard heaters and some hydronic kick heaters in the kitchen. 5 Zones. Since we moved in we've added a bunch of insulation and new windows.

Now that winter is coming we've started using the heat again. We noticed something strange. We've been keeping the thermostats set to 66f and the house seems really warm. Much warmer than 66.

So today I thought I should check the settings in the boiler to see what the previous owner did. Well it appears the heating curve set point is set to 82f. I'm guessing that's why it feels much warmer in here than 66? The boiler must be cranking the water temp way up. Does this make sense? They must have done this to compensate for the old leaky windows etc.

The slope is set to 1.4.

Am I safe to just lower the setpoint back down to 68f and see what kind of difference it makes in the house? Should I adjust the slope at all?

Redbaran

Slope has greater influence on the colder days of the season - the reference temperature (82 - assuming this is the number in the house icon) will adjust the anchor point of the heating curve (essentially where the curve starts) adjusting that down will reduce boiler water temp across the curve.

GGross

The room setpoint (your value 82f) shifts the entire heating curve up/down, It also controls the warm weather shutdown. factory setting is 68f (20c) I am 90% sure the slope of 1.4 is the factory setting. If I had to guess whoever installed it either didn't know how to change the slope, so they adjusted the room temp (I've seen this dozens of times), or the owner adjusted it to get the boiler to fire when it is warm outside. Just remember, higher room setpoint on the boiler will allow the boiler to fire at higher outdoor temps, lower values will cut it out at lower temps. If you have an indirect heater connected correctly to the boiler this value will not come into play for your DHW

What I do with mine is set the room temp for a couple degrees f above what I want my thermostat at, and then I will play with the curve over a heating season to get it set correctly. I prefer to set the curve just a little low to start, and move it up if needed. Most contractors don't want to make return visits so they just crank up one or more of the values, or they just disconnect outdoor reset and use a setpoint supply temp. IMO you want to get the most from the installed system so it is worth the time to use the ODR and adjust it if needed so you can actually condense and save some money.

Mbt93

https://forum.heatinghelp.com/discussion/comment/1817237#Comment_1817237

I turned it down to 70 and left the slope alone. Now that the boiler will heat to a lower temp will I notice my zones running longer? This is still going to be more efficient than hotter boiler temps but shorter zone run times? How will I know when I have the right slope and setpoint?

Thanks

GGross

Ideally you would lower the slope to the lowest setting that still maintains the indoor temp, this can be a bit difficult for some to do as there are other people in the house who might not like the temp dropping as you are finding the right setting. Considering you just dropped your room temp by so much I would see how your current settings work out for you as the temp drops. For baseboard heating I would expect you will end up raising the slope a bit, anywhere from 1.4 to 2.4 , I manage to set mine pretty low (can't remember exact setting off the top of my head, I have baseboard and wall panels mixed)

Familiarize yourself with the slope adjustment, they made it harder to adjust on that model as the contractors didn't like customers changing it on the previous model, the most recent model is back to being pretty intuitive

Mbt93

Being used to forced air..it's taking some time to get used to hydronic. Is the idea that you want the curve set so one zone is nearly always calling for heat but maintaining the setpoint? I have one large zone that's basically at that point with my current settings. The boiler would just maintain the lowest temperature at this setting using a very low amount of gas. I'm used to forced air where it's on full blast then completely off. So having something (the boiler) run continuously seems like it would use more gas than just cranking the water temp up when there's calls for heat.

GGross

Newer style furnaces run similarly, longer runtimes at lower fuel usage, generally the blower speed will be variable as well, this can bother customers used to that blast of hot air coming out the vents.

Basically the lower supply temperature allows your boiler to condense the flue gasses more, that is where a lot of the listed efficiency ratings are coming from, without condensing you might only be running 80-85% instead of 93-95% efficiency. The boiler modulates the burner, so while it might run for more time throughout the day, it won't be using more fuel than a system that runs less amount of time but cycles more, assuming all other things are equal. If one system is condensing, and the other is non-condensing, the condensing system will use less total fuel (less wasted energy going out the flue pipe) but the delivered btu/hr to the space should be the same over a day's worth of run time. With a condensing boiler install, or a modulating furnace, I like to see that system running at a low fire rate for a long time, while maintaining the indoor temp at the thermostat setting. When modulating forced air furnaces were a lot less common we used to get calls from contractors wondering why the furnace never shut off, so you are not alone being confused by this!

If you are running a fairly low heating curve setting your system may not recover quickly from temperature setbacks so do keep that in mind. The required water temp to maintain 70 degrees, is different than the required supply temp to raise the temp of the space several degrees. I do a 2 degree setback when I remember to dial back my thermostats (I don't have programmable stats) and don't have issues recovering from that. Temperature setbacks are one reason many contractors in the US set these condensing units to run at max temp on install, but then you basically have a modulating 80% boiler instead of a 95% one. Don't be shy to raise the heating curve if the system doesn't keep up. your comfort level should come first imo.

Mbt93

This a great info! It's all starting to make sense. Is there a temperature range where the boiler is condensing? I figured setbacks and a low heating curve wouldn't get along very well since it's really just able to maintain temp in the largest zone. We generally just set the thermostats to one temp most of the time anyways. Does the vitodens 100 up the temp if the call for heat is over a certain amount of time? With the heating curve low that large zone may call for heat for a very long time. No harm in having my Grundfos Alpha 2 running during these times which could be nearly continuous?

We have an outdoor camera that would always trigger motion when the boiler was exhausting flue gasses. Before making these changes at 25f outdoor temps it be a huge cloud that would be exhausting when running. Now the amount of exhaust is so minimal that it doesn't trigger the camera. Somewhat interesting.

GGross

You probably won't fully condense with baseboard, return water temperature is what you are concerned with, if you have a 20 degree delta t you will pretty much stop condensing with supply temps at about 160. Ideally return water is below 140, tough to get on the coldest days with baseboard.

There isn't a function to ramp up supply temp after a certain runtime on that one unfortunately

no harm running the pump as much as needed

Mbt93

You seem fairly knowledgeable with the settings on this boiler. I was checking all the settings and was wondering about these two:

setting - description - value

2 - Reduce max.heating output - 63

6 - Do not adjust! - 100

GGross

setting 2 is set by default to 63 for your size boiler, these share controls with 2 other boilers that have different fuel input rates, so this value limits the output to 63%, this doesn't actually limit your boiler to 63%, it allows it to full fire to its rated capacity, but the control is designed to work with other models with higher input values so this value is necessary for your boiler to function safely and correctly.

I never did learn what setting 6 is for, in my experience with their do not adjust values they exist for internal reasons only. the manual says the default value is 0 for that field, it may be worth double checking that you have wrote down the correct value and possibly calling tech support to confirm it. If I had to guess I would think this setting was never changed and is probably at the default setting, but it can't hurt to make sure. Usually these types of values in a viessmann control are combustion or ionization related and require changing at least one other setting to the correct value to "unlock" these, similar to how a fuel type adjustment is done.