Hello everyone,
some background on my questions:
I am currently exploring the possibility of converting our house from a gas heating system to a heat pump. It might sound completely crazy for a house that is just under 7 years old, but this could be funded and financed as an “energy renovation project” together with a photovoltaic system through KFW 261. That could actually make it economically very attractive.
I am still in the evaluation phase and have started initial discussions with heating and solar experts.
This immediately raised some questions for me, because the first offers are quite contradictory to the principles I often see discussed here in the forum:
The insulation level of the house is about KFW 55 standard; however, the overall standard was not met back then due to the gas heating system. The heating demand is around 12,000-13,000 kWh for a total of 270 square meters (2,900 square feet). There is underfloor heating throughout, including the basement.
Best regards,
Andreas
some background on my questions:
I am currently exploring the possibility of converting our house from a gas heating system to a heat pump. It might sound completely crazy for a house that is just under 7 years old, but this could be funded and financed as an “energy renovation project” together with a photovoltaic system through KFW 261. That could actually make it economically very attractive.
I am still in the evaluation phase and have started initial discussions with heating and solar experts.
This immediately raised some questions for me, because the first offers are quite contradictory to the principles I often see discussed here in the forum:
- Buffer tank (heating water) – Question: What exactly is the purpose of this and when does it make sense? So far, no seller has been able to clearly answer this, although the technical answer is simple: it should act as a hysteresis to reduce short cycling of the heat pump. The general idea is understandable, but I don’t really see how 100 liters (35 gallons) of buffer tank help when just the volume of my underfloor heating system already exceeds 200 liters (70 gallons), plus the large mass of screed acting as thermal storage. The current gas heating system works fine without a heating buffer tank.
- Heat pump capacity and modulation – the first quotes naturally come with absurdly oversized heat pumps because they only consider the total heated area of 270 square meters (2,900 square feet). When I point out that 12 or even 16 kW seems excessive, the answer is always: “It can modulate down from 3 to 12 kW.” That’s fine, but exactly this modulation is often warned against. So question: why is modulating down performance considered a problem? Is this the short cycling that people warn about? Technically, modulation means the entire system, including the compressor and all components, runs slower. But then the question arises how efficient it still is.
The insulation level of the house is about KFW 55 standard; however, the overall standard was not met back then due to the gas heating system. The heating demand is around 12,000-13,000 kWh for a total of 270 square meters (2,900 square feet). There is underfloor heating throughout, including the basement.
Best regards,
Andreas
Hello Andi,
Could you maybe share some figures regarding the financial aspect? We are in a similar situation. Until now, I thought it might be too early for switching from gas to a heat pump to be worthwhile, but I’m open to being convinced 🙂
KfW261: 20% of the total amount does not have to be repaid.
Based on the quotes you have, what price range are you seeing for a new heat pump?
Best regards
Could you maybe share some figures regarding the financial aspect? We are in a similar situation. Until now, I thought it might be too early for switching from gas to a heat pump to be worthwhile, but I’m open to being convinced 🙂
KfW261: 20% of the total amount does not have to be repaid.
Based on the quotes you have, what price range are you seeing for a new heat pump?
Best regards
Hello,
Simply replacing a gas heating system with a heat pump is only part of the solution. The idea is to also install photovoltaic panels on the roof, which dramatically improves the building’s KFW rating when combined with the heat pump. This way, achieving a 55 EE or even 40 EE standard should be quite feasible. The whole package will easily cost you around 50,000 Euros, but you get a repayment subsidy of 20-25% and the remainder is financed at just 0.31%, including the solar system. And that’s exactly the point: instead of financing costs of 4%, you only pay 0.31%. This means your solar system’s return on investment is no longer 20-25 years, but rather closer to under 10 years.
Whether this will be officially recognized by KFW remains uncertain, but that’s the current plan.
Best regards,
Andreas
FF2677 schrieb:
Could you maybe throw out some numbers regarding the financial aspect?
Simply replacing a gas heating system with a heat pump is only part of the solution. The idea is to also install photovoltaic panels on the roof, which dramatically improves the building’s KFW rating when combined with the heat pump. This way, achieving a 55 EE or even 40 EE standard should be quite feasible. The whole package will easily cost you around 50,000 Euros, but you get a repayment subsidy of 20-25% and the remainder is financed at just 0.31%, including the solar system. And that’s exactly the point: instead of financing costs of 4%, you only pay 0.31%. This means your solar system’s return on investment is no longer 20-25 years, but rather closer to under 10 years.
Whether this will be officially recognized by KFW remains uncertain, but that’s the current plan.
Best regards,
Andreas
Hello,
My heating system is supposed to have a LAN interface, but so far I haven’t been able to find it... ;-) Apparently, you have to open the casing to access it...
The supply temperature is low according to the heating curve:
32°C (90°F) at 0°C (32°F) outside,
36°C (97°F) at -10°C (14°F) outside, and
39°C (102°F) at -20°C (-4°F) outside.
That has always matched well. The thermometer on the supply side usually shows something between 32 and 37 degrees at typical winter weather (mostly between -5 and +5°C (23 and 41°F)), but it’s probably just an estimate.
Best regards,
Andreas
RotorMotor schrieb:
Maybe you can even check the maximum heating output there during winter?
Otherwise, just see how low you can set the supply temperature.
My heating system is supposed to have a LAN interface, but so far I haven’t been able to find it... ;-) Apparently, you have to open the casing to access it...
The supply temperature is low according to the heating curve:
32°C (90°F) at 0°C (32°F) outside,
36°C (97°F) at -10°C (14°F) outside, and
39°C (102°F) at -20°C (-4°F) outside.
That has always matched well. The thermometer on the supply side usually shows something between 32 and 37 degrees at typical winter weather (mostly between -5 and +5°C (23 and 41°F)), but it’s probably just an estimate.
Best regards,
Andreas
W
WilderSueden5 Oct 2023 11:30andimann schrieb:
Whether this will be approved by the KfW is still uncertain, but that’s the plan for now. I think the main challenge here is the building envelope. If you are aiming for the 55 standard, you should be able to manage it. But reaching 40 would require an uneconomical additional 2cm (1 inch) of insulation.
Hi,
Yes, this will be interesting. So far, I have spoken with two energy consultants, and both don’t see the situation as hopeless. I will probably have to get a completely new energy performance certificate. The current one is some generic version that the main contractor just issued back then. The calculations were based on T18 bricks, but it was actually built with T14 bricks.
At that time, I didn’t pay any attention to the energy rating and didn’t insist on an accurate calculation because the funding conditions from the KfW were not relevant for us then. From today’s perspective, a clear oversight on my part.
What we additionally need to insulate is the ceiling of the top floor, which currently has only 160 mm (6.3 inches) EPS insulation. The requirement is 240 mm (9.4 inches). I had planned this for two years already but never got around to it.
And then we’ll see what comes out of it...
Best regards,
Andreas
WilderSueden schrieb:
I think the key point here is the building envelope. If you’re in the 55 range, you should be able to manage it. But 40 would then require an uneconomical additional 2 cm (0.8 inches) of insulation.
Yes, this will be interesting. So far, I have spoken with two energy consultants, and both don’t see the situation as hopeless. I will probably have to get a completely new energy performance certificate. The current one is some generic version that the main contractor just issued back then. The calculations were based on T18 bricks, but it was actually built with T14 bricks.
At that time, I didn’t pay any attention to the energy rating and didn’t insist on an accurate calculation because the funding conditions from the KfW were not relevant for us then. From today’s perspective, a clear oversight on my part.
What we additionally need to insulate is the ceiling of the top floor, which currently has only 160 mm (6.3 inches) EPS insulation. The requirement is 240 mm (9.4 inches). I had planned this for two years already but never got around to it.
And then we’ll see what comes out of it...
Best regards,
Andreas
Hello,
Current update: Energy consultant 1 wants a slim €8,000 net for the calculation and "construction supervision" (i.e., certification that there is additional insulation on the top floor ceiling and that photovoltaic panels and a heat pump are installed)... That made me cough a bit longer.
That is about twice the cost of the inspector for the entire build...
He also wants €42,000 for a heat pump (Viessmann Vitocell 250 A)... The offer lists a staggering 132 man-hours of work. The plumber didn’t even need that long to install the entire gas heating system including underfloor heating during the build...
Crazy!
That’s not going to work out.
I am still waiting for feedback from energy consultant No. 2.
Best regards,
Andreas
Current update: Energy consultant 1 wants a slim €8,000 net for the calculation and "construction supervision" (i.e., certification that there is additional insulation on the top floor ceiling and that photovoltaic panels and a heat pump are installed)... That made me cough a bit longer.
That is about twice the cost of the inspector for the entire build...
He also wants €42,000 for a heat pump (Viessmann Vitocell 250 A)... The offer lists a staggering 132 man-hours of work. The plumber didn’t even need that long to install the entire gas heating system including underfloor heating during the build...
Crazy!
That’s not going to work out.
I am still waiting for feedback from energy consultant No. 2.
Best regards,
Andreas
Similar topics