ᐅ KfW 70 standard is not met, reference values for gas condensing boiler heating
Created on: 10 Apr 2014 22:35
R
rebenstorf
Hi everyone,
I need some advice from you. Our new single-family home is currently being calculated, and the person doing the calculations called me to say that the house doesn’t meet KfW 70 standards, which shocked me because I actually thought we would almost reach KfW 55.
Here are the house details:
186m² (2000 sq ft) living area
Basement floor insulation: 8cm (3 inches) XPS, 0.04 WLG (thermal conductivity)
Exterior wall structure: 1.5cm (0.6 inches) gypsum plaster, 24cm (9.5 inches) Poroton T16 bricks, 18cm (7 inches) mineral wool insulation with 0.035 WLG, 2cm (0.8 inches) air gap, 11.5cm (4.5 inches) clinker brick facade
Windows: triple-glazed, Ug 0.7
Roof insulation: 6cm (2.4 inches) continuous insulation above rafters, 24cm (9.5 inches) mineral wool between rafters at 0.035 WLG, 6cm (2.4 inches) insulation below rafters also 0.035 WLG
Heating system: Buderus GBH172 T75S 14kW gas condensing boiler with a 750L (198 gallons) buffer storage, five SKS 4.0 solar collectors at a 45° roof pitch, south orientation, no shading
Underfloor heating on ground and upper floors
I hope I haven’t forgotten anything. Based on the transmission heat losses alone, this should almost be KfW 55, but the heating system is also taken into account. Although it’s a gas condensing boiler, it should still meet KfW 70.
Since I’ve collected quotes from several home builders and construction companies, I know what they typically do to reach KfW 70—and none of them even included a ventilation system, usually only gas condensing boilers with domestic hot water production. Regarding insulation, none of the houses even matched our planned specs.
My question to the experts: Is the person doing the calculations correct? That would basically mean almost all house providers are exaggerating their numbers... or did she make a calculation error? I understand that no opinion here replaces an official calculation, but a rough assessment should be possible.
Thanks in advance!
I need some advice from you. Our new single-family home is currently being calculated, and the person doing the calculations called me to say that the house doesn’t meet KfW 70 standards, which shocked me because I actually thought we would almost reach KfW 55.
Here are the house details:
186m² (2000 sq ft) living area
Basement floor insulation: 8cm (3 inches) XPS, 0.04 WLG (thermal conductivity)
Exterior wall structure: 1.5cm (0.6 inches) gypsum plaster, 24cm (9.5 inches) Poroton T16 bricks, 18cm (7 inches) mineral wool insulation with 0.035 WLG, 2cm (0.8 inches) air gap, 11.5cm (4.5 inches) clinker brick facade
Windows: triple-glazed, Ug 0.7
Roof insulation: 6cm (2.4 inches) continuous insulation above rafters, 24cm (9.5 inches) mineral wool between rafters at 0.035 WLG, 6cm (2.4 inches) insulation below rafters also 0.035 WLG
Heating system: Buderus GBH172 T75S 14kW gas condensing boiler with a 750L (198 gallons) buffer storage, five SKS 4.0 solar collectors at a 45° roof pitch, south orientation, no shading
Underfloor heating on ground and upper floors
I hope I haven’t forgotten anything. Based on the transmission heat losses alone, this should almost be KfW 55, but the heating system is also taken into account. Although it’s a gas condensing boiler, it should still meet KfW 70.
Since I’ve collected quotes from several home builders and construction companies, I know what they typically do to reach KfW 70—and none of them even included a ventilation system, usually only gas condensing boilers with domestic hot water production. Regarding insulation, none of the houses even matched our planned specs.
My question to the experts: Is the person doing the calculations correct? That would basically mean almost all house providers are exaggerating their numbers... or did she make a calculation error? I understand that no opinion here replaces an official calculation, but a rough assessment should be possible.
Thanks in advance!
R
rebenstorf12 Apr 2014 11:16Hi
My idea to do it this way came after I visited someone who had done the same as I am doing now, while I was still living in my old house. The temperature in their attic was 21.8°C (71.2°F) and in mine it was 26.2°C (79.2°F) on the same day and at the same time, and I think these are clear arguments. The location and building features were pretty similar.
And you’re right, it’s not the task of insulation to store heat, but if I have the option to achieve both with one insulation material, why not. You can try entering my roof construction into a U-value calculator and compare it with a conventional one, and you will see a noticeable difference in heat protection. And if you don’t trust the calculator, which is completely understandable, then I can only refer you back to the practical example of 21.8°C compared to 26.2°C.
Best regards from Lower Saxony
Bauexperte schrieb:
Basically, the insulation effect does not increase linearly with the thickness of the insulation material; in my opinion, you could have saved that money.
**Regarding summer heat protection: the purpose of insulation materials is to reduce heat transfer, not to store heat. A good solution for the roof area is so-called overlay insulation (insulation installed over the rafters), which fully encases the entire structure from the outside. This provides excellent protection against intense heat in summer, and is cost-effective since less thickness is required.
My idea to do it this way came after I visited someone who had done the same as I am doing now, while I was still living in my old house. The temperature in their attic was 21.8°C (71.2°F) and in mine it was 26.2°C (79.2°F) on the same day and at the same time, and I think these are clear arguments. The location and building features were pretty similar.
And you’re right, it’s not the task of insulation to store heat, but if I have the option to achieve both with one insulation material, why not. You can try entering my roof construction into a U-value calculator and compare it with a conventional one, and you will see a noticeable difference in heat protection. And if you don’t trust the calculator, which is completely understandable, then I can only refer you back to the practical example of 21.8°C compared to 26.2°C.
Best regards from Lower Saxony
That depends on the roof construction in the old apartment. Otherwise, it’s like comparing apples and oranges using some random data you found for your calculations here.
Just discuss it with the people involved in your house planning. They should know best where errors might occur. Trying to piece together potentially hazardous half-knowledge on your own doesn’t help.
Just discuss it with the people involved in your house planning. They should know best where errors might occur. Trying to piece together potentially hazardous half-knowledge on your own doesn’t help.
R
rebenstorf12 Apr 2014 12:01Hello
The roof construction of the old house is as described above, only 18cm (7 inches) of glass wool insulation between the rafters, and for the other house, it will be as I want it to be, also described above.
And here, I only wrote what I measured myself with the thermometer. There’s no gathered “stuff” and no apples and oranges mixed.
My question about achieving the KfW 70 standard was only whether the missing values could be the reason or not.
Regarding the people who do the calculations, I have already spoken with them, and they say there is no mistake; therefore, I just wanted to ask for a general opinion on this forum because, with these values, I simply could not imagine that KfW 70 wouldn’t be achieved, and then I would possibly consult someone else for a calculation.
If the answer had been here that it is only possible with gas heating and, given the wall and roof construction, it is highly unlikely to reach KfW 70, I would have saved myself the trouble of a new calculation.
Regards
emer schrieb:
That depends on the roof construction in the old apartment. Otherwise, it’s like comparing apples and oranges with the calculations you put together from various sources here.
.
The roof construction of the old house is as described above, only 18cm (7 inches) of glass wool insulation between the rafters, and for the other house, it will be as I want it to be, also described above.
And here, I only wrote what I measured myself with the thermometer. There’s no gathered “stuff” and no apples and oranges mixed.
My question about achieving the KfW 70 standard was only whether the missing values could be the reason or not.
Regarding the people who do the calculations, I have already spoken with them, and they say there is no mistake; therefore, I just wanted to ask for a general opinion on this forum because, with these values, I simply could not imagine that KfW 70 wouldn’t be achieved, and then I would possibly consult someone else for a calculation.
If the answer had been here that it is only possible with gas heating and, given the wall and roof construction, it is highly unlikely to reach KfW 70, I would have saved myself the trouble of a new calculation.
Regards
R
rebenstorf12 Apr 2014 12:16Hi,
a brief addendum.
I only responded to the question about the roof construction because someone asked why it was designed that way.
That’s all there is to say on that topic. The rest is about achieving the KFW 70 standard.
Regards
a brief addendum.
I only responded to the question about the roof construction because someone asked why it was designed that way.
That’s all there is to say on that topic. The rest is about achieving the KFW 70 standard.
Regards
R
rebenstorf12 Apr 2014 12:45Some structural engineering and energy consulting firm. Was commissioned by the homeowner.
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