What is the optimal condensation temperature for a CO furnace?

It also seemed a lot to us, so I started to read what I was doing wrong.
Last season I burned in an old coal (or actually coke) cast iron boiler. About 6-7 tons of coal were burned during the year. Mom and wife like to be warm at home, so the comfortable temperature is around 23 degrees Celsius, and it is still cool for them.

The house was insulated at the end of November. In fact, the insulation is not finished yet, because the plaster will be applied in the spring, 15cm graphite polystyrene is used.
The attic, and in fact the space between the ceiling and the roof, is not well insulated so far, currently there is 8 cm thick wool.

I am also asking for a hint on how to set DHW heating. There are two bathrooms and two showers in the house. 150L tank, the maximum temperature is set to 48 degrees and there is no shortage of hot water. It can be said that while dripping in the shower, I do not have to let cold water in. Is it better to set it to a higher temperature, maybe then the boiler will heat the water in the tank less often, but more intensively.

If you have enough hot water, it makes no sense to keep, for example, 60 degrees non-stop (the mixers would also be required to avoid accidentally getting burned).

But look for a weekly heat-up mode in the boiler, it may be called anti-legionella mode. This must be done to kill any bacteria with that name from the tray.

You are thermophilic, I currently have 39 degrees in the 2F boiler, which is heating water, and I do not mix with cold either.

Well, if you go 6-7 tons of coal, you burn gas "more or less" reasonable amounts compared to coal. You will improve warming and combustion will decrease.

miro.t wrote:

it's about 23 degrees, and it's still cool for them

I have so much at work and it is a bit too much for me.
The question is whether you have non-stop warm radiators, because comfort decreases when the radiator is warm and cold.
The best effect is when the radiator is still slightly warm.

miro.t wrote:

150L tank, the maximum temperature is set to 48 degrees and there is no shortage of hot water. It can be said that while dripping in the shower, I do not have to let cold water in.

I have 38 degrees set on the 2-function boiler and sometimes when the water overheats to 40 degrees I have the impression that it is too hot, at 48 it would be hot.
Or you have losses along the way because the pipes are not insulated etc.
Maybe the old radiators are covered with limescale and other deposits and are inferior in efficiency.
After changing the boiler, it was necessary to rinse the installation so that the siphons would not end up in the exchanger of the new boiler, because this may also reduce the efficiency of the gas boiler.
In principle, you should have a magnetic filter on the heating return just in front of the boiler, acting as a desilter cleaning the central heating system

The heat demand of a building is influenced by thermal insulation and the occurrence of thermal bridges, etc., and you will not change this without thermal modernization.
The only thing you can reduce the losses on the installation, i.e. ensure a clean installation, it is also worth having a hot water tank with adequate power and good thermal insulation and low standstill losses, etc.
In the case of coils, its surface is important, the larger the better. If you have DHW circulation, you can only turn it on at a certain time.
With the boiler, it heats up in one place, and then the heat is distributed throughout the house, so you can try not to overheat certain rooms.
There are many elements to consider.
In private, I usually notice a tendency to overheat flats and houses, but this is my subjective feeling.

This is great topic: 0 interesting things I learned thanks to my friends.

I wonder what it looks like with you. Do I have low fuel consumption or is it better?
Until now, I was heating with coal, eco-pea coal, a furnace with a feeder, steel panel radiators and copper pipes, the combustion was about 10 tons for the whole year.

Now, the first winter after changing to gas heating, a thermagen solo 18 stove with a weather station with a 120l tray, I immediately insulated the house. 1973 PRL cube. 150 m2 of heated surface, 15 cm of polystyrene, graphite 33 and I replaced the windows and doors in accordance with the 2021 standard. In the attic, 4 cm of polystyrene and 12 cm of wool.
At the moment it's -5 to -12 outside. The average fuel consumption is 0.4 m3 per hour over 3 days. At home, the temperature is 22 degrees.
When it was about 0 degrees, the combustion was about 0.33 m3 / h. A maximum of 59 degrees is set on the stove.
Please write me your experiences. Whether my fuel consumption is high or low. Is 59 on the stove a lot or a little. Is it working optimally or something can be improved.
I am learning this furnace, so please be understanding.
Thanks for all the information.

t0mi wrote:

At the moment it's -5 to -12 outside. The average fuel consumption is 0.4 m3 per hour over 3 days. At home, the temperature is 22 degrees.
When it was about 0 degrees, the combustion was about 0.33 m3 / h. A maximum of 59 degrees are set on the stove.

I can not determine the average combustion per hour because my boiler works for several hours a day and in severe frosts it sucked up to 7-9 m3 a day in lighter 4-5 and set the economy under the instructions of the furnace as condensing is 55 down from what I remember on my for several I am 46 years old and it is enough for 120 sq m of living space. This attic is a bit thin, it is insulation or insulation.

t0mi wrote:

Is 59 on the stove a lot or a little

That's a lot for me is 40st.

tom.pk wrote:

That's a lot for me is 40st.

One installation will heat up to -20 to 40 degrees on the boiler, and another, in the same frost, will need, for example, 70 degrees. It all depends on the type of installation (underfloor heating or radiators) and, in the case of radiators, their power at a given supply temperature and return to the current demand.

t0mi wrote:

When it was about 0 degrees, the combustion was about 0.33 m3 / h. A maximum of 59 degrees are set on the stove.
Please write me your experiences. Whether my fuel consumption is high or low. Is 59 on the stove a lot or a little. Is it working optimally or something can be improved.
I am learning this furnace, so please be understanding.
Thanks for all the information.

Do you have additional thermostatic heads on the radiators? If so, you can try to flatten the heating curve so that the max is e.g. 50 degrees. If it will not reheat for the most frosts, then set 55 etc (trial and error method)

The lowest possible return temperature is recommended for a condensing boiler, which is indirectly related to the flow temperature. You can gain a few% on combustion.

A really better effect (about 8% for each degree) would be to lower the temperature in the house to 21-20 degrees, but I don't know if this is acceptable for you or your family members.

Note that condensation is affected by the return temperature, not the flow temperature. Condensation occurs when the return temperature does not exceed 56 degrees (i.e. the flow temperature can successfully be higher). Let's say that at 20 degrees frost it will be appropriate to set 70/55 degrees (supply / return), but such temperatures are really rare (it can be winter, when such a temperature does not occur at all - even one night), they read with this setting with an average winter of 0 degrees) it will be 50/40, and no. in March or November 40/35, if not less.

How do I determine the return temperature? Measure it, can the furnace feel it and I can display it?

Added after 7 [minutes]:

Wojewoda82 wrote:

tom.pk wrote:

That's a lot for me is 40st.

One installation will heat up to -20 to 40 degrees on the boiler, and another, in the same frost, will need, for example, 70 degrees. It all depends on the type of installation (underfloor heating or radiators) and, in the case of radiators, their power at a given supply temperature and return to the current demand.

t0mi wrote:

When it was about 0 degrees, the combustion was about 0.33 m3 / h. A maximum of 59 degrees is set on the stove.
Please write me your experiences. Whether my fuel consumption is high or low. Is 59 on the stove a lot or a little. Is it working optimally or something can be improved.
I am learning this furnace, so please be understanding.
Thanks for all the information.

Do you have additional thermostatic heads on the radiators? If so, you can try to flatten the heating curve so that the max is e.g. 50 degrees. If it will not reheat for the most frosts, then set 55 etc (trial and error method)

The lowest possible return temperature is recommended for a condensing boiler, which is indirectly related to the flow temperature. You can gain a few% on combustion.

A really better effect (about 8% for each degree) would be to lower the temperature in the house to 21-20 degrees, but I don't know if this is acceptable for you or your family members.

I have thermostats, and I don't know how to set it up, a lot of variables.

t0mi wrote:

How do I determine the return temperature? Measure it, can the furnace feel it and I can display it?

Just read on the driver. Every normal driver shows such a parameter.
For me, 55 degrees is rarely on the power supply (maybe at -20 degrees outside), let alone on the return.

Brencik wrote:

Just read on the driver. Every normal driver shows such a parameter.

In my Vaillant VUW240 / 2-5 boiler, there is no return temperature reading, although there is a sensor and the boiler takes into account its readings during its operation.
I can only read the flow temperature, i.e. when the burner is turned off, the flow temperature automatically becomes the return temperature.

t0mi wrote:

How do I determine the return temperature? Measure it, can the furnace feel it and I can display it?

you must state in your boiler manual whether you have such a parameter as the return temperature.
But the boiler return temperature is the average return temperature from the radiators, and it is influenced by the pump efficiency, the degree of valve opening on the radiators, the flow temperature, the minimum boiler power, and the current demand for power from the heated building.

t0mi wrote:

Is 59 on the stove a lot or a little.

it is a relative concept.
According to my estimates, 40-45 degrees would be enough for me, but with non-stop heating.
Since my boiler has a minimum power of 9kW, it must be switched on in cycles, when the boiler heats up, for example, 15 minutes, there is no chance to maintain these 40-45 degrees and the water heats up to 56, because I have a maximum of 56 degrees on the boiler in an apartment in the old , uninsulated building.
My perception of body comfort is such that I would most prefer a floorstand, where you cannot feel the source of heat, and yet it is warm.
I can feel the heat source with the radiators, especially when the radiators heat up to a maximum of 56 degrees.
If, in the future, I have a boiler with a minimum power of 3kW, then in frosts, the boiler burner will be able to work around the clock with a power of approx. 3kW and then they will be able to keep these 40-45 degrees constantly, because there will be no need to heat with impulses and heat the water to 56 degrees .
If I wanted the single cycle of the burner operation in the boiler to be longer, I would have to increase the temperature, which for me would be a deterioration of comfort, because the temperature fluctuations increase.
These 56 degrees are too much for me, but I have no other option.
Setting a lower temperature means a lower dose of energy during one burner cycle, and therefore more frequent boiler switching.

The main thing is to focus on your comfort, because looking for savings usually means a deterioration of this comfort.
I have a friend who thinks that he pays little for heating, but for him, sitting in the fleece in the room while watching TV is a norm, and this does not meet my comfort requirements.
On the other hand, in another friend's hut it is constant around 24 degrees, which for me is definitely too warm.
So everyone has their own sense of comfort.

Or maybe set a lower temperature after all. The stove will switch on more often, but the thermal comfort will be better.

Hello, I'm going to hijack this thread because it's the same topic. My first heating season and first stove in my life. House 120m2 floor only, acc. project demand 6kw, Termet Gold plus 25kw 2f furnace with Solus wireless room sensor and no additional pumps or clutches. Overall, 2 levels unusable attic, including a living room, ground floor 3 rooms, first floor, 2x1 bathrooms, vestibule, garage, 2x1 corridors, ground floor tiles, first floor panels, roof insulated with PUR foam. I did not play with rotamers, they are between 1.5-2. After heating the floor, I increased the temp. currently min 16.8 (moon) max 19.4 (sun) and started adjusting the furnace. Works OK. On the stove set 34 at the outside around 0st on the return measured with an ordinary thermometer (unless you can see in the stove) 22st, i.e. a difference of 12st. it's over 27% and I read somewhere that the best is between 15-20%. Heats 2x for 5 hours from 5-10 and 18-23. The house cools down 0.2 degrees every 2.5 hours (measured from 10:00 to 12:30). During this time, it runs all the time and does not clock, the flame on the controller is visible at a standstill. Sometimes it will turn off an hour earlier because it reaches 19.4 degrees. On colder days, when the -6 does not feel warm at night, it reaches 18.8. I expect it is due to the low supply temperature of 34 degrees, unless it is still regulated on the rotameters. Gas consumption Lm between 6.5-7.5m3 for these 10 hours of operation at these positive temperatures. The question is whether this is the maximum that can be obtained in terms of consumption and comfort, not temperature (he lives only), only hardware - rotameters, dT, etc. Parameters that I set P01 10 P03 30, service set 88 P04 slightly reduced from 1500 to 1200 P05 56 so set the service on the meter I did not move dT 5, service set 6 P14 40 P18 80 was set by the service on the gauge P24 3 factory rest

What else can you do? The stove turns on for a while after unscrewing the cold water, flushing (hot water) - is it normal, did the plumbers do something wrong to me? It should only be warmer. Is 34/22 condensation ok?

pajky wrote:

On the stove set 34 at the outside around 0st on the return measured with an ordinary thermometer (unless you can see in the stove) 22st

read the manual, the boiler should show the return temperature, so you don't have to measure it with an ordinary thermometer, which is unreliable, because it's hard for me to imagine a difference of 12 degrees with an efficient floor heating system.

As for condensation and efficiency, the manufacturers give the highest values for the return temperature of 30 degrees and the supply temperature of 50, but this applies to radiators.
Only the factory boiler has a hysteresis of 5 degrees, i.e. if you set 34, the boiler can heat water up to 39 degrees before it turns off the burner due to exceeding the temperature of the boiler (heating) water.
Do you want to test it yourself and set a lower temperature, pay attention to whether it will not cause the boiler to clock.
There should be comfort and the boiler should work in continuous mode without clocking every few minutes, and the issue of condensation is secondary and will be the result of what your installation offers.
Even if we take into account only a few degrees of difference, having 34 on the supply, it will be about 30 on the return, so you don't have to worry about condensation.

pajky wrote:

The stove turns on for a while after unscrewing the cold water, flushing (hot water) - is it normal, did the plumbers do something wrong to me?

the plumbers did not put a non-return valve on the cold water supply in front of the boiler. Without it, you probably have a temporary backflow and the flow sensor reads this water movement as an alleged hot water consumption
Add a non-return valve to the cold tap water supply to the boiler and the problem should go away.

>>10121233

Could you give me a hint how to effectively set the set parameters on the BM-2?
Services for Wolf boiler are very few and this is my first condensing boiler.
In a house of 115m2 I have a Wolf FGB24 boiler installed with BM-2.
All floor + ladders in bathrooms + thermostats in each room.
What supply temperature to set and whether anything else to turn off such as savings factor.

Hello!
I had a BM-1, but this new one is probably very similar.
I don't know how the settings could look at the floor, I had radiators, a little oversized and the building is quite heavily insulated, but without going crazy.
The curve is set at 0.9, but I gave a fairly strong correction for the impact of the room so that at the beginning went quite a large temperature on the radiators and then as the room temperature increased, it decreased so as not to quickly exceed the set temperature and turn off the heating. It is known that it is better for the heating to run non toper, even at a very low temperature in the radiators, otherwise, despite the hysteresis of only 0.5 degrees, heating in jumps is very uncomfortable. This is due to the fact that the sensation of heat at a temperature of, say, 20.8 st in the case of a walking boiler and warm radiators is higher than if it were 21.2 st and cold radiators.
The rest of the settings less important. Of course, to come to such conclusions it took a long time, several seasons, to optimally embrace this. Also important is the place where the controller is set up, so that it is not in a room exposed to overheating from the sun or a lot of people staying at once.
For a house of 115 m2 would be enough boiler with a maximum of a few kW, the most important thing is the minimum power it has. In my case it was about 3 kW and it was too much because most of the time during the heating season the temperatures are positive anyway and the power needed for heating is max 2 kW. In your case, these 24kW will be a huge problem, unless the boiler starts from a power of 1.5 kW which I doubt.

Installations, even if there are thermostatic valves on radiators, need to be adjusted, i.e. flows on radiators, because this affects the return temperature.
If a radiator close to the boiler has too high a flow, it will automatically increase the return temperature, so the boiler will have to operate at higher parameters to heat more distant radiators, and it may also overclock too strongly.
A long time ago, I provided a heating diagram with an "additional" return pipe. In fact, there does not need to be much of this additional pipe, because it depends on the design of the system, which can be corrected before it is installed.
The idea is that the first radiator in the supply should be connected to the return as the last one, and each other radiator should be connected to the return according to its order on the riser.
If the installation runs around the apartment, instead of directing the return along the same route as the power supply, route it further around the apartment to the boiler, so that the riser, for example, goes around the apartment clockwise and the return counterclockwise. Then the arrangement as above will work itself out - the first radiator on the riser will be the last one on the power supply. The flows will be self-regulating and there is no need to correct the flows with radiator return valves, and the boiler will have the best possible return temperature.

The temperature on the Immergaz stove is "output" or "inlet"... I mean setting it so that condensation works

I have already written many times (and others have also written) that condensation depends only on the RETURN temperature (the power supply has no influence on condensation) and for it to occur, the RETURN temperature should not exceed +56 degrees. The supply temperature is always higher than the return temperature. Let's say that for the heaviest frosts you can set the power supply to max. 70 degrees, return max. 55 (there will still be condensation), and such frosts are rare (usually 20 degrees below zero are considered severe frosts), i.e. in average winter conditions (e.g. temperature around zero) the parameters will be much lower (e.g. 50 degrees on the power supply and 40 on the return), and in November and March (positive but low temperatures) - even lower.

Ok, thank you for the information - where can I get the "return temperature" / I'm sorry for such a question, but I'm a layman in this topic - thank you in advance for your answer.

Is there no thermometer on the installation showing the return temperature? Should be. In any case, the return temperature is always LOWER than the supply temperature, because the water returns to the boiler already slightly cooled (the radiators gave it heat to the room).

55 degrees, I didn't even have power at -20

>>20837814
I don't have an additional thermometer anywhere, only the one on the Immergas Zeus 25 stove. That's why I had questions...

I'll straighten it out a bit here, because condensation is not equal to CONDENSATION. What is it about? It's going to be a bit physical.

Condensation of water vapor from the exhaust gases of a condensing gas boiler results from the relative content of water vapor in the exhaust gases of the boiler and from the temperature point at which the relative water vapor content reaches 100% (I ignore the water vapor content above 100% that can be achieved, e.g. in the laboratory) . For a properly adjusted condensing gas boiler, the 100% relative humidity in the exhaust gases is at approximately 57 degrees (this also depends somewhat on whether the boiler draws dry or humid combustion air).


When the boiler exchanger has a temperature lower than the dew point for these exhaust gases, e.g. 50 degrees, the "excess water vapor content in the boiler exhaust gases" (that which cannot be contained in the temperature of 50 degrees in these exhaust gases) will condense on the exchanger, transferring the energy of the phase transformation of water from gaseous to liquid to the exchanger. The more condensed the exhaust gas temperature is on the cooler exchanger (lower exchanger temperature), the more water vapor will condense per m3 of exhaust gas.

Assuming that we have a well-set mixture composition, there is a significant difference between the exchanger return temperature of 55 degrees, 50 degrees, 40 degrees and 30 degrees. The possible energy recovery from condensation varies greatly. The energy of the phase transformation of water from the gaseous state to the liquid state is 2.27MJ/kg of condensed water, or 0.63kWh. When burning 1 m3 of gas, a boiler needs about 12 m3 of air, which means it emits about 13 m3 of exhaust gases (to put it simply, the exhaust gases are warmer).

So by burning 1 m3 of natural gas, we can additionally obtain on condensation:

To start with, air at a temperature of 57 degrees and a relative humidity of 100% contains just over 114g of water per m3

When the return temperature is 55 degrees, then (assuming ideal energy exchange in further calculations) with a relative humidity of 100% again, the water content in m3 of exhaust gases drops to less than 105 g, i.e. we would get a maximum of 0.009 kg per m3 of exhaust gases, i.e. 0.009 x 13 x 0.63kWh gives a condensation yield of 0.074kWh

When the return temperature is 50 degrees, the water vapor content in the exhaust gases drops to 83g, i.e. we gain 0.032kg per m3 of exhaust gases, i.e. the condensation gain is 0.26kWh

When the return temperature is 40 degrees, the water vapor content in the exhaust gases drops to 51g, i.e. we gain 0.063kg per m3 of exhaust gases, i.e. the condensation gain is 0.516kWh

When the return temperature is 30 degrees, the water vapor content in the exhaust gases drops to 30 g, i.e. we gain 0.084 kg per m3 of exhaust gases, i.e. the condensation gain is 0.688 kWh

The above calculations also explain why floor installations and low temperature supply (and therefore low return) are the most effective.

I used a relative and absolute humidity calculator:
https://www.otech.pl/kalkulator-wetosci/


Finally, you know that in the summer, when it is muggy (high humidity), you take a drink out of the fridge or pour a cold drink into a glass, water condenses on the glass. Because in muggy weather, such as 80% humidity at 30 degrees, the dew point is 26 degrees, water will condense on elements with a temperature lower than this.

The same experiment, but when the air is dry (e.g. in winter with radiators, when it's frosty outside and ventilation is a problem, the relative humidity can drop to 30% or less without humidification) when the temperature in the apartment is 20 degrees (and the humidity is 30%). dew point is below 2 degrees C.


This also explains the problem with fungus in some houses and apartments:
- faulty ventilation
- windows too tight, no air exchange
- many "humidity generators" (many residents, drying laundry in the apartment, the latter is not a problem like the others, ok, if the air is too dry, you can humidify the laundry)
- walls too cold, i.e. freezing, not insulated or too narrow, even with a relative humidity of e.g. 50% and a temperature in the apartment of 20 degrees, the dew point is just over 9 degrees, sometimes the walls, e.g. in frost, can be colder, then it literally pours water after them.

Thank you for a very interesting and factual explanation of condensation. This is a nice approach to the topic. I didn't know where to check the temperatures / I still don't know physically how to read them on the Immergas Zeus 25 furnace / I'm not an installer or service technician, just an ordinary user of the furnace - it's just that, and here it displays the variable temperature during the furnace operation and which one is which...? I ONLY HAVE ONE DISPLAY ON THE STOVE. Although I know that the first one should be up to 57 C because only then there is a condensation effect, I don't know where to read the second one??? The manual also doesn't indicate where to read it... I really liked your answer and thank you very much and have a nice day

Hello The owner replaced the old furnace with Buderus gb072 24k + controller rc310. Apartment about 96m2 with radiators. I would like to ask for help with the furnace settings from what I can see it is set to 82°C on the furnace. How to set the furnace? From the menu of the controller I checked the temperature on the radiators is set to a maximum of 65. Currently, with the temperature outside around -1 to +4 degrees, consumption is about 13m3 per day, set temperature 20.5 during the day and 19.5 at night. Gliwice on radiators turned to max in the room with the controller

24kW to 96 m2? Either crazy or someone fooled him.
82 deg is some abstraction, with the current weather I estimate it should be something around 45 deg, unless he has 2 small radiators for the whole shed.
How come the temperature on the radiators is 65 deg when it is 82 on the furnace?

Maybe I'll describe it this way. I live abroad and I've seen a lot, I don't know a lot about it, so I'm certainly not surprised that it looks like the work of a crazy serviceman. It probably is, just how to embrace it now.
A first floor apartment, overhead neighbors. A large living room/kitchen and 2 rooms, where the door is open only at night, locked. In the living room 3 radiators + one small one in the hallway open, in the rooms each 1st.
The menu of the rc310 controller looks like this, I changed both parameters to 45 and on the furnace, just to be sure, also after pressing the heater icon also to 45.
I don't understand why one parameter is referred to as the maximum heating temperature and the other as the maximum temperature for the radiators, because to me layman they are the same thing.

The weather at night was 6 degrees, from 3 to 7 pm consumption of about 7m3.
As I wrote, radiators turned up to the max, because I treat the whole thing as one room.
I forgot to write my goal is to maintain a constant temp for 24 h i.e. During the day 20.5-21 at night 19.5-20 month old baby in the house and all day someone is staying.

It would be best if some Buderus specialist would comment, I am not familiar with this controller.