ᐅ KfW 70? New construction – which heating system, air-to-water heat pump, underfloor heating, KfW 85 instead of KfW 70
Created on: 14 Jul 2013 19:16
S
snaky80
Hello everyone,
I am currently planning a semi-detached house of about 120m² (1290 sq ft) turnkey from the general contractor. The plot is about 280m² (3014 sq ft). Like many others, I am feeling overwhelmed by all the information I have been reading. However, I am still not making much progress regarding the heating system.
First, some details about the house:
Currently offered:
Concrete slab with 60mm (2.4 inches) Styrodur (thermal conductivity 0.035 W/mK)
The house will mostly be clad with facing bricks (small plaster areas) – 140mm (5.5 inches) insulation KD 035, mineral wool with vapor barrier
Silicate plaster on Poroton bricks
Currently planned for a single-flue chimney (not yet finalized, possibly later!)
Floors: Ground floor – screed about 65mm (2.6 inches) on 90mm (3.5 inches) insulation
Floors: Upper floor – screed about 65mm (2.6 inches) on 60mm (2.4 inches) insulation
Attic floor laid with OSB boards (200mm (7.9 inches) thermal insulation WLG 035 fully bonded vapor barrier)
Insulation: upper floor between rafters 200+50mm (7.9 + 2 inches), in the collar beam area 140mm (5.5 inches) insulation WLG 035
Windows: 5/6 chamber profile, U-value = 0.6
The heating system currently planned:
Air-to-water heat pump – Viessmann Vitocal 200-s heat pump, output 7.7 kW
Vitocell CVA 300-liter (79 gallons) domestic hot water storage tank
Underfloor heating on ground and upper floors
Now to the main point:
It would be great to reach the KfW 70 standard, but I’m not a fan of an air-to-water heat pump. I would rather switch to a gas condensing boiler with solar support and domestic hot water assistance. (According to my calculations, the annual cost of a gas boiler would be only slightly higher!)
The builder told me that the KfW 70 standard cannot be reached with this setup, only KfW 85.
It would require additional heating support from the solar system – which is not really worthwhile.
Or alternatively, including a ventilation system in the calculation. Both options would add about €10,000 more.
That is, of course, a significant amount. Could anything be improved in the insulation to reach KfW 70?
Or should I simply forgo KfW 70 and choose a solid KfW 85 variant, just with gas plus solar for hot water?
I am happy to hear any suggestions...
Best regards,
snaky80
I am currently planning a semi-detached house of about 120m² (1290 sq ft) turnkey from the general contractor. The plot is about 280m² (3014 sq ft). Like many others, I am feeling overwhelmed by all the information I have been reading. However, I am still not making much progress regarding the heating system.
First, some details about the house:
Currently offered:
Concrete slab with 60mm (2.4 inches) Styrodur (thermal conductivity 0.035 W/mK)
The house will mostly be clad with facing bricks (small plaster areas) – 140mm (5.5 inches) insulation KD 035, mineral wool with vapor barrier
Silicate plaster on Poroton bricks
Currently planned for a single-flue chimney (not yet finalized, possibly later!)
Floors: Ground floor – screed about 65mm (2.6 inches) on 90mm (3.5 inches) insulation
Floors: Upper floor – screed about 65mm (2.6 inches) on 60mm (2.4 inches) insulation
Attic floor laid with OSB boards (200mm (7.9 inches) thermal insulation WLG 035 fully bonded vapor barrier)
Insulation: upper floor between rafters 200+50mm (7.9 + 2 inches), in the collar beam area 140mm (5.5 inches) insulation WLG 035
Windows: 5/6 chamber profile, U-value = 0.6
The heating system currently planned:
Air-to-water heat pump – Viessmann Vitocal 200-s heat pump, output 7.7 kW
Vitocell CVA 300-liter (79 gallons) domestic hot water storage tank
Underfloor heating on ground and upper floors
Now to the main point:
It would be great to reach the KfW 70 standard, but I’m not a fan of an air-to-water heat pump. I would rather switch to a gas condensing boiler with solar support and domestic hot water assistance. (According to my calculations, the annual cost of a gas boiler would be only slightly higher!)
The builder told me that the KfW 70 standard cannot be reached with this setup, only KfW 85.
It would require additional heating support from the solar system – which is not really worthwhile.
Or alternatively, including a ventilation system in the calculation. Both options would add about €10,000 more.
That is, of course, a significant amount. Could anything be improved in the insulation to reach KfW 70?
Or should I simply forgo KfW 70 and choose a solid KfW 85 variant, just with gas plus solar for hot water?
I am happy to hear any suggestions...
Best regards,
snaky80
... why I chose the condensing boiler with solar @€uro, as I mentioned at the beginning, I am not a fan of an air-to-water heat pump. I don’t want an unsightly and noisy outdoor unit in the garden... The air-to-water heat pump is just as impractical as the heating support with the solar system. If I need warm air in winter for the air-to-water heat pump, it simply isn’t available. Then I would have to operate the heating using the electric heating element. At that point, I might as well use a tankless water heater.
Gas condensing technology is a well-established method, and there is more experience available in this field. Can anyone say today that an air-to-water heat pump lasts longer than a condensing boiler? I don’t think so.
Sizing the system at 19 kW was the heating engineer’s suggestion, with the reasoning that the boiler heats up faster...
@Nutshell – where exactly did the Viessmann boiler rank first (which test?)
How do the other manufacturers perform?
Best regards
Gas condensing technology is a well-established method, and there is more experience available in this field. Can anyone say today that an air-to-water heat pump lasts longer than a condensing boiler? I don’t think so.
Sizing the system at 19 kW was the heating engineer’s suggestion, with the reasoning that the boiler heats up faster...
@Nutshell – where exactly did the Viessmann boiler rank first (which test?)
How do the other manufacturers perform?
Best regards
snaky80 schrieb:
... Designing the system for 19kW was the heating engineer's suggestion, based on the reasoning that the boiler would heat up faster... If you fall for salespeople whose main interest is their own profit, you end up with costly "recommendations" like these overall. Regards
Hi
What exactly is supposed to heat up faster?
KfW 70 basically means underfloor heating, low supply temperature, and gradual but consistent warmth. It doesn’t require much power.
Fast heating of domestic hot water is also not a problem with an appropriately sized water tank. Only in cases of many occupants and a tank that’s too small would this be a consideration—but then it would make more sense to choose a larger tank rather than oversizing the heating system for a rare eventuality.
It’s better to have a precise heating demand calculation done first and then size the system accordingly.
bye
Explosiv
who also opted against a heat pump and chose a gas condensing boiler with solar for domestic hot water
What exactly is supposed to heat up faster?
KfW 70 basically means underfloor heating, low supply temperature, and gradual but consistent warmth. It doesn’t require much power.
Fast heating of domestic hot water is also not a problem with an appropriately sized water tank. Only in cases of many occupants and a tank that’s too small would this be a consideration—but then it would make more sense to choose a larger tank rather than oversizing the heating system for a rare eventuality.
It’s better to have a precise heating demand calculation done first and then size the system accordingly.
bye
Explosiv
who also opted against a heat pump and chose a gas condensing boiler with solar for domestic hot water
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