ᐅ KfW70 heat pump, underfloor heating, ventilation system, and photovoltaic panels

Hello everyone,

We are planning to build a KfW 70 house and would like to install an air-to-water heat pump with underfloor heating as well as a photovoltaic system.
We would appreciate your professional opinion on the required size of the heat pump. The house will have approximately 140 sqm (1507 sq ft) of living space.

Additionally, we would like to have a fireplace in the living room.

I am unsure whether we definitely need a mechanical ventilation system in this house to prevent mold growth.

Is there really a risk if, for example, we go on vacation and do not ventilate regularly, or is this more of a concern with passive houses?

Thank you in advance for your help!

Best regards,
Silke

Hello,

catweazlecat schrieb:
...we are planning to build a KFW70 house and would like to install an air-source heat pump with underfloor heating and a photovoltaic system.

KFW70 and Proxon probably do not match well, unless you are prepared to face high operating costs in the long run!

catweazlecat schrieb:
...We would also like your professional opinion on the required sizing of the pump. The house is planned to have about 140sqm (1507 sq ft) of living area.

For this, you need a mechanical and electrical engineering (M&E) design, or you have to rely on the often unreliable information from salespeople.

catweazlecat schrieb:
...Now I am unsure whether we definitely need a ventilation system in this house to keep it free of mold.

Not necessarily, but it offers significant comfort during "normal" use, heat recovery is possible => sometimes a system with one performance level lower is sufficient (and cheaper), savings on heating surface area, hydraulics, which can offset the additional costs overall.

Best regards

€uro schrieb:
Hello,
KfW 70 and Proxon probably don’t fit well together, unless you want to live with high energy costs in the long run!
For this, you need mechanical, electrical, and plumbing (MEP) planning, or you can rely on the unsubstantiated claims of salespeople.
Not necessarily, however, it provides significant comfort with “normal” use, heat recovery is possible => sometimes the heat generator can be one performance level smaller (cheaper), savings on the room heating surfaces, hydraulics, so the additional costs balance out overall.

Best regards.

What exactly do you mean by Proxon?

KayLinus schrieb:
What do you mean by Proxon?

It seems a post got misplaced here. How that happened is a mystery to me!

Best regards

catweazlecat schrieb:

We are planning to build a KFW70 house and would like to install an air-to-water heat pump with underfloor heating and a photovoltaic system.

Additionally, we would like to have a fireplace in the living room.

Now I am uncertain whether we definitely need a ventilation system in this house to keep it free of mold.

Is the risk really significant if, for example, we go on vacation and cannot ventilate regularly, or is this more of an issue with passive houses?

I can only share a layperson’s opinion and experience: we also have a KFW70 (actually an unconfirmed 55) house with an air-to-water heat pump, mechanical ventilation with heat recovery, underfloor heating, and photovoltaics. Our photovoltaic system is connected to the household electricity, not to the heat pump, so it’s unrelated to the heating system.
The mechanical ventilation system is worth the money for us. Of course, there are costs for filters and especially electricity, but the comfort is great. Whether your house will develop mold without mechanical ventilation, no one can say for sure. It depends on how much moisture will accumulate inside if you don’t ventilate. That’s speculation. Most of my neighbors have KFW70 houses without mechanical ventilation and have had no mold after 2.5 years. However, that won’t help you if your walls develop mold after two years.
We also planned for a fireplace; we installed only the chimney flue so far, but don’t have the stove yet. Since our house is generally very warm anyway, the fireplace is mainly for aesthetic reasons, which we have put aside for now. A water-heated fireplace would have been uneconomical for us due to the additional technical and hydraulic systems required.
Ventilation systems and fireplaces are a topic on their own. Our ventilation system can easily be connected to a pressure switch that shuts it off if underpressure occurs. You should definitely discuss this during your planning phase.

Hello Wastl,
your post almost sounds like the answer I’m looking for. We are currently planning to build a prefab house with Bien-Zenker.
The floor area is 70m² (750 sq ft) on the ground floor and 70m² (750 sq ft) upstairs, where the bedrooms and bathroom are located. Since our house isn’t very large, we were recommended a WFKA system from Proxon, which can also provide cooling in the summer. I have read that it might cause problems with floor areas over 90m² (970 sq ft) and isn’t really designed for that. Since we don’t mind the cold, I hope that according to the calculations the WFKA will suffice for us. The house is a KFW70 Passive House. In the bathroom, I want to install separate underfloor heating beneath the tiles—currently we have this only for warm feet during winter, which is enough for us.
In theory, you shouldn’t need to ventilate the house more, but my wife likes to open the windows a lot. I assume we will rarely have to operate the system. Does anyone else have a Proxon WFKA?