Heat pump: buffer tank, capacity and modulation

Hello Andi,
Could you maybe throw a few numbers into the ring regarding the financial aspect? We’re in a similar situation, until now I thought that switching from gas to a heat pump wouldn’t pay off this early, but I’m happy to be convinced :)
Kfw261: not having to repay 20% of the amount.
Where are you currently landing according to offers for a new heat pump?
Regards

Hello,

Could you maybe throw some numbers out there regarding the financial aspect?

Just swapping the gas heating for a heat pump is only half the fun. The idea is to also slap photovoltaic panels on the roof, which dramatically improves the KFW rating of the house in combination with the heat pump. This way, a 55 EE or even 40 EE standard should be easily achievable. The whole package will easily cost you €50k, but you get 20-25% repayment subsidy on that and the rest financed at 0.31%, including the solar system. And that’s exactly the point: instead of 4% financing costs, you only have 0.31%, and with that your solar system no longer has an ROI of 20-25 years but rather you end up with under 10 years again.

Whether this will be accepted by KFW like that is still up in the air, but that’s the plan for now.

Best regards,

Andreas

Hello,

Maybe you can even read the maximum heating output there in winter?

Otherwise, just see how low you can set the flow temperature.

My heating system is supposed to have a LAN interface, but unfortunately, I haven't found it yet.... ;-) Apparently, you have to open the casing to get to it...

The flow temperature is low, according to the heating curve
at 0°C outside at 32°C
at -10°C outside at 36°C and
at -20°C outside at 39°C.

That always matched. The thermometer in the flow shows something between 32 and 37 degrees during the usual winter muck weather (usually between -5 and +5 °C), but that's probably more of a rough estimate.

Best regards,

Andreas

Whether this will be recognized by KFW is still up in the air, but that is the plan for now.

I think the crux here is the building envelope. If you are in the 55 range, you should be able to manage it. But 40 would then require an uneconomical 2 cm more insulation.

Hi,

I think the key point here is the building envelope. If you're in the 55 range, you should be able to make it. But 40 would then require an uneconomical 2 cm more insulation.

Yes, this will be exciting. So far, I have spoken with two energy consultants and both don’t seem to see the situation as hopeless. I will probably have to get a completely new energy certificate made. The existing one is a generic one that the general contractor just issued back then. It was calculated with T18 bricks but built with T14. I didn’t care about the energy rating back then at all and didn’t insist on an exact calculation because the KFW conditions were totally uninteresting to us at that time. From today’s perspective, a clear oversight on my part.

What we additionally need to insulate is the upper floor ceiling, which currently only has 160 mm EPS. 240 mm is required. I have had this planned anyway for two years but never got around to it.

And then we’ll see what comes out of it...

Best regards,

Andreas

Hi,

current status update: Energy consultant 1 wants a slim €8000 net for the calculation and "construction supervision" (= certification that there is more insulation on the top floor ceiling and that photovoltaic and heat pump are installed)... I had to cough for a while over that. That is well double the cost of the inspector during the entire construction...

He also wants €42k just for a heat pump (Viessmann Vitocell 250 A)... The offer mentions a staggering 132 man-hours of work. The plumber didn’t need that long during the house construction to install the entire gas heating including underfloor heating...

Insane!

That’s not going to work like that.

I am still waiting for feedback from energy consultant No. 2.

Best regards,

Andreas