ᐅ Offer for KfW 70 house – KfW 55 with additional controlled residential ventilation – is a KfW 70 too airtight?
Created on: 30 Aug 2016 14:34
K
Kaspatoo
Hello,
I received the attached offer from a developer.
It is a KfW 70 house with a gas boiler.
To achieve KfW 55, it is sufficient to install either a controlled residential ventilation system for an additional €12,400 (about USD equivalent) instead of the gas boiler, or even just a decentralized ventilation system with heat recovery for only the kitchen/living room and bathroom for €6,500 (about USD equivalent) — meaning the bedrooms would have no ventilation.
Now I am wondering: wouldn’t the KfW 70 offer be too airtight or sealed to operate properly without any ventilation?
If KfW 70 is enough for me, where can I save costs or where can I reduce insulation?
We want to use brick cladding and not polystyrene panels, but mineral wool instead.
Can the hollow bricks be made thinner? Can simple bricks be used instead of hollow bricks?
Can thinner mineral wool be used?
Thank you very much for your answers.
I received the attached offer from a developer.
It is a KfW 70 house with a gas boiler.
To achieve KfW 55, it is sufficient to install either a controlled residential ventilation system for an additional €12,400 (about USD equivalent) instead of the gas boiler, or even just a decentralized ventilation system with heat recovery for only the kitchen/living room and bathroom for €6,500 (about USD equivalent) — meaning the bedrooms would have no ventilation.
Now I am wondering: wouldn’t the KfW 70 offer be too airtight or sealed to operate properly without any ventilation?
If KfW 70 is enough for me, where can I save costs or where can I reduce insulation?
We want to use brick cladding and not polystyrene panels, but mineral wool instead.
Can the hollow bricks be made thinner? Can simple bricks be used instead of hollow bricks?
Can thinner mineral wool be used?
Thank you very much for your answers.
Hello.
So, 6500 euros for a decentralized ventilation system is quite confident pricing. It’s basically a few holes in the exterior wall plus about 300 to 600 euros for each fan and a cable.
The additional cost for an air-to-water heat pump combined with a mechanical ventilation system with heat recovery (is the LWZ this combined unit?!) doesn’t seem completely excessive to me. However, you will likely have higher heating costs compared to a gas heating system.
Is the small subsidy for KfW 55 still worth it in this case?
Best regards,
andimann
So, 6500 euros for a decentralized ventilation system is quite confident pricing. It’s basically a few holes in the exterior wall plus about 300 to 600 euros for each fan and a cable.
The additional cost for an air-to-water heat pump combined with a mechanical ventilation system with heat recovery (is the LWZ this combined unit?!) doesn’t seem completely excessive to me. However, you will likely have higher heating costs compared to a gas heating system.
Is the small subsidy for KfW 55 still worth it in this case?
Best regards,
andimann
BeHaElJa schrieb:
It probably depends somewhat on the number of devices... 10 devices with covers, protective caps, wiring, control, and warranty...+ Switches and core drilling (around €100 each, for example)
Decentralized systems are not that cheap either. A realistic price would likely be closer to around €500 per unit.
Kaspatoo schrieb:
What is airtightness?
The energy consultant said you need to aim for around 0.6.
My general contractor says the blower door test usually results in somewhere between 1 and 1.5.
.Our blower door test showed 0.3... we also don’t have a mechanical ventilation system and ventilate manually. After one year, no mold has appeared yet... waiting to see. Friends built with the same construction company and masonry structure in 2011. They achieved KfW 55 standard... also only window ventilation. No mold so far...
We usually only ventilate in the morning after getting up and briefly in the evening before going to bed (but only in the bedrooms then)...
Similar topics