Importance of outdoor temp sensor for reset on Viessmann Vitodens B1KE-120 ?

ThinkpadUser7

I'm currently having a Viessmann Vitodens B1KE-120 installed in Palo Alto.

I'm wondering if I should have the included outdoor temp sensor installed and enabled.

Here's what the heating company said:

"We could but we found it a bit problematic at times and customers don't really tend to use it so 95% of the time we come back to remove it . Keeps the boiler from running as temperature rises throughout the day some people like the warm floors. Totally up to you."

Any thoughts on this decision?

mattmia2

It is heating radiant flooring? If customers are having a problem with it they aren't setting it up properly.

If it were heating fancoils or fintube baseboard that would be a different story.

ThinkpadUser7

yes, radiant flooring. I guess he means that customers prefer the boiler to keep running so the floor temps don't drop?

mattmia2

I think they(the installer) just aren't setting the reset curve properly. If you have the right curve it should run constantly at a temp that matches the heat loss of the building or pretty close to that.

KC_Jones

They have decided to not take the time to tune it in properly so their solution is to blame the control instead of taking the responsibility to learn how to do their job.

The floors "get cool" because the outdoor reset isn't tuned in. The goal is to put just enough heat into them to maintain indoor temperature of the house. If it is turning the floors on and off, it's not dialed in and needs tweaking.

My guess, they want to install it, set it to some nominal or factory default setting and walk away. The reality is it needs to be tuned per house and per owner, it could take a month or two to get it dialed in, possibly all winter. For me, it's 100% worth it, gives maximum comfort and efficiency, if the tuning is done to get it working correctly.

How did they size that boiler? Unless this is a huge house, that seems like a lot of boiler for Palo Alto.

ThinkpadUser7

It's a combi boiler (limited space) that provides both DHW and radiant. It's my understanding that this is a challenging balancing act because DHW has higher needs. This boiler provides 3.3 gallons per minute with a 77 degree rise. The house is only 1300 square feet (two full baths), but the Viessmann turns down to 12k BTUs. I believe this is actually the smallest combi that Viessmann makes.

ThinkpadUser7

Logic for sizing below. I had asked why another company quoted a larger combi unit:

"Current boiler is 75k btus and 38kbtu water heater I’m not sure why they quoted you such a large boiler. 3.3 USG/min (757 L/h) for B1KE-120
* At Δ t = 77°F (43K). Maximum DHW supply temperature is 140°F (60°C) per code typical shower heads should be limited between 1.5-1.7gpm. you have 2 full bathrooms as long as we stay within range of the max continuous draw of the boiler we are ok."

GGross

I would have recommended a tank to go with it personally, they hook up really easy to the equivalent non-combi version of that boiler, and you used to have a tank somewhere so there is room. you will probably be satisfied with the combi though.

In regards to outdoor reset, I would want it hooked up for a radiant floor especially. It is really easy to disconnect it and set a setpoint for the boiler, but whatever setpoint is correct for that boiler, is only needed during the coldest day of the entire year, every other day it could be lower allowing for more even floors and longer boiler runtime, as well as possibly increased efficiency. It is almost a guarantee that the setpoint that ends up being chosen will be too high for even the coldest day.

Your contractor probably had customers that don't fully understand how the system is designed to work, so they want to set a temp to avoid a callback. Personally I think educating the customer and getting a feel for what they want from their system is critical for a new boiler install. You will know if someone truly needs a setpoint or not.

You can also very easily adjust the heating curve if needed throughout the course of a heating season, generally within a heating season you can have it dialed in really well. If a contractor were to set up with the app it would be possible for them to monitor and adjust the heating curve remotely, however I do not know a single contractor that utilizes this very handy functionality (understandable as we aren't all tech savvy)

You as the owner can adjust this value very easily yourself, most contractors would not want you to touch it, personally I think owner training on a new boiler is very valuable so they have less chance of doing something bad to it if they have an understanding of the things they should not touch at all. it is 3 button presses to access the heating curve adjustment, and just adjust up or down 1-2 values at a time until you are happy, keep in mind any changes are not noticeable immediately and should be adjust in small increments with a few hours in between at least. use the viessmann recommended for your maximum so you don't turn it too high ( 0.8 is a good setting to not exceed for radiant floors)

ThinkpadUser7

Thanks for all the info. I am asking them to hook up the outdoor sensor.

Re: a separate tank, I did have one before, but it was blocked by the boiler which made service a real pain in that the boiler needed to be completely removed. There was probably some creative way to fit a small separate tank (above or below), but every person I talked to suggested a combi after seeing the size of the space.

mattmia2

Viessman and Buderus make horizontal indirect tanks.

GGross

Not sure on the Buderus ones but the Viessmann horizontals are quite a bit more money than the vertical equivalent. I always figured it was because they were designed to have a boiler mounted on top of them

ThinkpadUser7

GGross said:

You as the owner can adjust this value very easily yourself, most contractors would not want you to touch it, personally I think owner training on a new boiler is very valuable so they have less chance of doing something bad to it if they have an understanding of the things they should not touch at all. it is 3 button presses to access the heating curve adjustment, and just adjust up or down 1-2 values at a time until you are happy, keep in mind any changes are not noticeable immediately and should be adjust in small increments with a few hours in between at least. use the viessmann recommended for your maximum so you don't turn it too high ( 0.8 is a good setting to not exceed for radiant floors)

Video capture of Vitodens install seminar:


You mean value should be less than or equal to 0.8 ?
That would limit the max water temps to about 125 F and it would typically be less than 100 F in a Palo Alto winter?
My old system got the temp up to 150 F I think, assuming the dial was accurate.

mattmia2

You probably will need to experiment since your old system isn't typical of what would be installed today assuming this is the same system that boiler from the ~40's had heated. There might have been some mixing on that system to get the temp to the floor down lower, you don't want that with a mod con, the old boiler needed to keep the return water temps up so it wouldn't condense. You want the opposite with a mod con, the lower the return water temps the better the efficiency.

Big Ed_4

Yes, you want the outdoor reset , with your boiler and radiant heating , it will run your system on peak efficiency . For the higher temperature heating it will mellow the heat cycle for comfort . . Maybe 20% savings annually x how many years ...

Alan (California Radiant) Forbes

I like to set the heating curve low and see if it keeps the house warm, but no mater how I explain the concept, many homeowners often think I didn't install the system properly, so I don't experiment anymore and set the heating curve to a higher number.

Crazy to not use the outdoor reset feature.

If anything, it's fun to play with.

ThinkpadUser7

Alan (California Radiant) Forbes said:

I like to set the heating curve low and see if it keeps the house warm, but no mater how I explain the concept, many homeowners often think I didn't install the system properly, so I don't experiment anymore and set the heating curve to a higher number.

Crazy to not use the outdoor reset feature.

If anything, it's fun to play with.

Should I start with 0.8? It sounds like that's the upper range of the slope for radiant applications. I could try lowering over time to see if I notice a difference.

mattmia2

if the thermostat cycles off frequently try a lower number. if it isn't warm enough try a higher number. your old system was directly fed off of some ancient boiler or maybe even an early tankless water heater which isn't the normal way to do it. it is possible the thermostat was satisfied before the system ever reached the setpoint of the aquastat

ThinkpadUser7

mattmia2 said:

if the thermostat cycles off frequently try a lower number. if it isn't warm enough try a higher number. your old system was directly fed off of some ancient boiler or maybe even an early tankless water heater which isn't the normal way to do it. it is possible the thermostat was satisfied before the system ever reached the setpoint of the aquastat

Thanks, good to know.

Here's the old boiler:


Due to safety concerns I wouldn't run it for very many hours at a time and it would never actually get to the thermostat temp. But after a few hours it would start a cycle where it would be off for 4 minutes, on for 11 minutes, off for 4 minutes, etc. I think this was when it had reached the setpoint of the aquastat.

Everything in that closet is being ripped out and replaced with a combi on the back wall.

mattmia2

I'm not sure i see a relief valve anywhere in there and it almost looks like the vent between the appliance and the transite vent is just a piece of asbestos paper.

ThinkpadUser7

mattmia2 said:

I'm not sure i see a relief valve anywhere in there and it almost looks like the vent between the appliance and the transite vent is just a piece of asbestos paper.

The relief valve was there, but it was behind the metal boiler exhaust in the photo.

I had an asbestos removal place remove the following this morning: transite flue, the other metal vent + outer attached paper, and a piece of asbestos on the interior of the closet door.

Mad Dog_2

Without it, you might as well stayed with an atmospheric boiler.  If they are installing State of the Art products, it's time they jump in with both feet. Mad Dog 🐕 

ThinkpadUser7

Mad Dog_2 said:

Without it, you might as well stayed with an atmospheric boiler.  If they are installing State of the Art products, it's time they jump in with both feet. Mad Dog 🐕 

edit: I removed a response of mine that I realized made no sense after I did more research ... carry on and thanks for your input

GGross

Are you sure the video you watched specifically covered the new E series boilers? the curve you posted is different than the one in the E series install manual, most radiant floors are designed to run below about 120 F for reference, most flooring shouldn't take a supply above 140 but this depends, you may have less insulation under your tubing etc. The lower the temperature you can use and still maintain the living space will generally equal a more comfortable home, this can be something that takes a couple of attempts to get nailed down correctly, which is why many contractors don't like to do it, they rather move on to the next job.

ThinkpadUser7

GGross said:

Are you sure the video you watched specifically covered the new E series boilers? the curve you posted is different than the one in the E series install manual, most radiant floors are designed to run below about 120 F for reference, most flooring shouldn't take a supply above 140 but this depends, you may have less insulation under your tubing etc. The lower the temperature you can use and still maintain the living space will generally equal a more comfortable home, this can be something that takes a couple of attempts to get nailed down correctly, which is why many contractors don't like to do it, they rather move on to the next job.

This is where I got it from: https://youtu.be/wIbQVskkyh0?si=zjkzcrIypw95apqB&t=3606 (starting around 1 hour mark). The video is a couple years old though.

GGross

Huh the values are a bit different than the manual lol. I would go based on what comes shipped with the boiler though.

mattmia2

oh, and I would turn off any auto feeders and make sure the system holds pressure for a few days to make sure it isn't leaking since radiant systems of that vintage frequently eventually develop a leak somewhere under the slab. Want to make sure it isn't leaking before you replace the boiler.

ThinkpadUser7

mattmia2 said:

oh, and I would turn off any auto feeders and make sure the system holds pressure for a few days to make sure it isn't leaking since radiant systems of that vintage frequently eventually develop a leak somewhere under the slab. Want to make sure it isn't leaking before you replace the boiler.

Yeah, about a month ago I did some basic pressure testing where I shut off the gas to the boiler, waited a couple days for the water to cool, closed the fill valve, and then observed the pressure over the next week. Pressure seemed to hold fine, so I think it's ok.

exqheat

Outdoor restes are not intuitive to the heat loss of the building. Thay are a close second, but not as intuitive as modern indoor resets.

GGross

That would require purchasing separate devices, and in this case it would need to be 3rd party and would eliminate the technology already in the boiler that is already paid for. The boiler also doesn't have a 0-10v input to regulate water temperature so you would need to set it for the highest setpoint needed and turn the boiler on/off to achieve the correct temperature the 3rd party controller calls for, which would result in short cycling. the exact things we are trying to avoid in this case

mattmia2

@GGross I thought Viessman had 0-10v control but called it something else.

GGross

mattmia2 said:

@GGross I thought Viessman had 0-10v control but called it something else.

The 200 series has a 0-10v. Older Viessmann equipment utilized 0-10v but instead of the 0-10 correlating to a burner operating percentage it corresponded to a setpoint temperature. Viessmann doesn't like external controls operating their burner. I believe the new 0-10v is more in line with US needs but not entirely sure.

You may be thinking about the european "open therm" which I am pretty sure is very similar to how we use 0-10v controllers. Viessmann used open therm controls as their own form of room feedback or indoor reset. most of the 200 series boilers have this capability if I'm not mistaken.

mattmia2

Controlling the setpoint makes way more sense than controlling the burner firing rate in a mod con. That is what you want is different temps of water based on the load.

exqheat

"That would require purchasing separate devices, and in this case it would need to be 3rd party and would eliminate the technology already in the boiler that is already paid for."

If it's wrong, change it. The savings will pay for it, and the comfort is priceless.

ThinkpadUser7

Reading through the manual it says this for "Heating Curve":

Heating curves illustrate the relationship between the
outside temperature, the target room temperature and the
supply temperature. The lower the outside temperature,
the higher the supply temperature.

(from https://www.viessmann-us.com/content/dam/public-brands/ca/pdfs/doc/b1he/vitodens_100-b1he_oi.pdf/_jcr_content/renditions/original./vitodens_100-b1he_oi.pdf)



But the chart just shows supply temp vs outside temp, so I don't understand how target room temp is involved with these curves. Assuming my system is set to 0.8 slope with an outside temp of 32 degrees F, wouldn't that dictate that the supply temp should be roughly 100 F regardless of target temp (ignoring the fact that if target temp is exceeded boiler will shut off?)

It seems like the slope decision is about heat loss, not target temp.

GGross

@ThinkpadUser7
in the graph shown 68f is being used as the target indoor temperature (they usually illustrate this better). If you adjust the target indoor temperature the whole chart moves up/down. The target indoor temp will control your warm weather shutdown.

"Assuming my system is set to 0.8 slope with an outside temp of 32 degrees F, wouldn't that dictate that the supply temp should be roughly 100 F regardless of target temp"

For this example if you were to raise the "target indoor temp" since the whole graph would move "up" those supply temperatures would change as well

GGross

exqheat said:

"That would require purchasing separate devices, and in this case it would need to be 3rd party and would eliminate the technology already in the boiler that is already paid for."

If it's wrong, change it. The savings will pay for it, and the comfort is priceless.

It's not wrong though. I agree your product is a great product, that does not make every other product a bad product though, or every install without indoor reset "wrong" .

exqheat

No doubt. Problem is, customers are being decieved by a concept that does not work and is poorly installed. OR's have been arround for 75 years. They never did well. Ask Einstein.

mattmia2

The heat loss varies with solar gain and wind so there are settings for modifiers to the reset curve on most boilers that will do things like increase the setpoint if the heat call lasts over a certain time. If the boiler has a room thermostat instead of just a contact closure it can make better decisions but i'm not sure how many actually do that.

ThinkpadUser7

GGross said:

@ThinkpadUser7
in the graph shown 68f is being used as the target indoor temperature (they usually illustrate this better). If you adjust the target indoor temperature the whole chart moves up/down. The target indoor temp will control your warm weather shutdown.

"Assuming my system is set to 0.8 slope with an outside temp of 32 degrees F, wouldn't that dictate that the supply temp should be roughly 100 F regardless of target temp"

For this example if you were to raise the "target indoor temp" since the whole graph would move "up" those supply temperatures would change as well

Ok, that makes more sense. Thanks for the explanation.

I'll post some photos later, but the installation was finished yesterday. I still need to hook up the app (ViCare?), but I was told that the slope had been set at 0.7.

So far I have two concerns: 1. Gas usage seems high and 2. There's a bit of an annoying medium pitched drone audible through much of the house when the boiler is running

1. Gas Usage

I think the system was initially fired on around 3pm. At the time the interior temp was showing as 64. We set the target temp to 67. A couple hours later the floors were checked with an infrared camera, which showed the pipes as yellow but the thermostat still showed 64. I wrote down the reported therm usage at the gas meter at around 6pm. Around 8pm the interior temp had increased to 65 and at 10pm it was still at 65. I looked at the gas meter again and usage had increased by 2 therms over those 4 hours. Only a tiny amount of hot water was used during that period, probably less than a gallon. At this point I lowered the target to 65 and the boiler shut off. As far as I know it hasn't come on since, though I haven't checked the meter yet today.

I should note that I'm pretty sure the house maintains heat well. In the past after running radiant for 24 hours during a period where nights got down to ~40 F, the house maintained a comfortable 67 F for 3+ days with the boiler being shut off.

So the radiant heating was running at ~50k BTUs per hour? What's surprising is my 1947 boiler used about .5 therms per hour while running (with aquastat set to something like 150 F), so I would have expected this new one to use less gas. Perhaps I need to lower the heating curve? I'm hoping I can do all these adjustments in the app.

2. Noise

When I'm standing right in front of the boiler it doesn't sound very loud, but throughout maybe half of the 1300 square foot house you can definitely hear it. A low rumble wouldn't really bother me but there's a higher pitched element that's a bit annoying. The walls to the closet are interior walls to the house, and they have no insulation, but the fact that I can hear it in a bathroom, which is down the hall and around the corner makes me think that perhaps the noise is being transmitted through the attic. We do have bat insulation above the ceiling but it might not cover air vents, light fixtures, etc. i also don't know what it looks like now right above the new PVC flue that was put in (replacement for old transite flue).

That's probably enough rambling for now, but I'll post photos later today. I am really happy with how the installation looks and it appears very serviceable to my untrained eyes (lots of valves, spigots, gauges, etc). Pipe routing seems like it was well thought out too.

GGross

When you take pictures can you show how the venting is done as well. You also can't really compare the fuel usage between the two appliances while one is maintaining a temperature, and the other is recovering several degrees, generally you need to compare usage over a season, or monthly to get a more accurate reading of it, there are too many variables without a controlled environment to properly compare over the course of a single hour, or a couple of days

You shouldn't be able to hear the boiler running in general, installation on interior uninsulated walls can sometimes carry a ton of vibration though. When I do startups on these for contractors I have to take off the cover because they don't believe they are running lol

exqheat

"The heat loss varies with solar gain and wind so there are settings for modifiers to the reset curve on most boilers that will do things like increase the setpoint if the heat call lasts over a certain time."

Why not just control the heat from the thermostat information?