ᐅ Which Heating System Is Suitable for a Multi-Family House If a Heat Pump Is Not Eligible for Incentives?
Created on: 24 Apr 2023 17:18
D
deri254
Hello,
since early 2020, I have been building a multi-family house (4 apartments with a total living area of 435 sqm (4,680 sq ft) over 2 floors, underfloor heating) in Bavaria. The energy efficiency standard is just about KfW55. At that time, I did not apply for any subsidies because I have done everything myself except for the roof structure, so I only purchased the materials. In 2020, the only option for me was to install an oil heating system. However, given the developments in recent months, the only sensible option now would be a heat pump. Since I did not apply for any funding before the start of construction in 2020, as far as I know, it is no longer possible to get subsidies for the much more expensive heat pump. Or is there still a possibility in my case to receive funding for the heat pump? Otherwise, my only option would be to install an oil or gas heating system (the latter with a biogenic liquid gas tank in the garden) before the end of the year.
Another detail: 10 meters (33 feet) away on another parcel, there is my farmhouse, completely renovated and somewhat insulated between 2014 and 2017 (approx. 118 sqm (1,270 sq ft) living area over 3 floors, with radiators), but still using a 25-year-old oil heating system. Last year, as a precaution during sewer works, I already installed a thermal pipeline between the two houses up to the boiler room. Here, funding for replacing the heating system would be possible. Would it therefore be conceivable to easily get subsidies if both houses were run with a single heating solution? According to the heating installer, a heat pump for the renovated house would not be without challenges.
Thank you.
since early 2020, I have been building a multi-family house (4 apartments with a total living area of 435 sqm (4,680 sq ft) over 2 floors, underfloor heating) in Bavaria. The energy efficiency standard is just about KfW55. At that time, I did not apply for any subsidies because I have done everything myself except for the roof structure, so I only purchased the materials. In 2020, the only option for me was to install an oil heating system. However, given the developments in recent months, the only sensible option now would be a heat pump. Since I did not apply for any funding before the start of construction in 2020, as far as I know, it is no longer possible to get subsidies for the much more expensive heat pump. Or is there still a possibility in my case to receive funding for the heat pump? Otherwise, my only option would be to install an oil or gas heating system (the latter with a biogenic liquid gas tank in the garden) before the end of the year.
Another detail: 10 meters (33 feet) away on another parcel, there is my farmhouse, completely renovated and somewhat insulated between 2014 and 2017 (approx. 118 sqm (1,270 sq ft) living area over 3 floors, with radiators), but still using a 25-year-old oil heating system. Last year, as a precaution during sewer works, I already installed a thermal pipeline between the two houses up to the boiler room. Here, funding for replacing the heating system would be possible. Would it therefore be conceivable to easily get subsidies if both houses were run with a single heating solution? According to the heating installer, a heat pump for the renovated house would not be without challenges.
Thank you.
So far, there is no thermal protection certificate because I have done everything myself and without applying for subsidies, I didn’t need one. I have only compared the U-values of KfW55 and KfW70 standards and mine is somewhere in between. Here are my (approximate) values:
U-value for 36.5cm (14 inches) Ytong wall: 0.24
U-value for floor slab insulation with 12cm (5 inches) insulation: 0.26
Roof with 8cm (3 inches) Pavatex and 20cm (8 inches) insulation between rafters: 0.15
Windows: 0.89
Roof windows: 1.10
A friend of mine, for his single-family house, took a higher capacity especially for hot water because, according to him, it is often problematic. He already chose a 12kW heat pump. My building material supplier also entered the data into their software and came up with 30kW.
Is 14kW really enough? And which one would you recommend?
In addition, my photovoltaic feed-in tariff ends in 2027. As it stands now, selling electricity would no longer be profitable, and then the 23kW system would be available for hot water or a buffer tank.
U-value for 36.5cm (14 inches) Ytong wall: 0.24
U-value for floor slab insulation with 12cm (5 inches) insulation: 0.26
Roof with 8cm (3 inches) Pavatex and 20cm (8 inches) insulation between rafters: 0.15
Windows: 0.89
Roof windows: 1.10
A friend of mine, for his single-family house, took a higher capacity especially for hot water because, according to him, it is often problematic. He already chose a 12kW heat pump. My building material supplier also entered the data into their software and came up with 30kW.
Is 14kW really enough? And which one would you recommend?
In addition, my photovoltaic feed-in tariff ends in 2027. As it stands now, selling electricity would no longer be profitable, and then the 23kW system would be available for hot water or a buffer tank.
Heating demand according to Google on several platforms:
KfW-55 house 35 kWh/m², KfW-70 house 45 kWh/m²
That means for me approximately 42 kWh/m² of living space. With my living space of 435 m² (4681 ft²), that's about 18.27 kW. Adding around 20% for domestic hot water results in about 22 kW.
So I would need a heat pump with at least 22 kW, right? How do you arrive at only 14 kW for my living space?
My heating engineer acquaintance roughly calculated a 24 kW boiler for oil or gas heating with my data.
KfW-55 house 35 kWh/m², KfW-70 house 45 kWh/m²
That means for me approximately 42 kWh/m² of living space. With my living space of 435 m² (4681 ft²), that's about 18.27 kW. Adding around 20% for domestic hot water results in about 22 kW.
So I would need a heat pump with at least 22 kW, right? How do you arrive at only 14 kW for my living space?
My heating engineer acquaintance roughly calculated a 24 kW boiler for oil or gas heating with my data.
I would like to propose the thesis that a 12 kW heat pump is sufficient to heat the multi-family house.
From my own difficult experience, heating engineers tend to recommend oversized heat pumps. The reason is simple: it heats quickly and reliably, design flaws are easily covered up, and the customer only realizes much later that this results in a lower overall efficiency with frequently cycling heat pumps.
An experience value from a multi-family house with the following key data:
Multi-family house, 475 m² (5115 ft²) with 4 residential units and 8 occupants:
Some building component values:
Wall 0.15 W/m²K
Windows 0.75 W/m²K
Roof 0.11 W/m²K
The final energy consumption of the multi-family house is 15.8 kWh/(m²*a). The house has a relatively large window area of about 170 m² (1830 ft²).
Heating is provided by a 12 kW ground-source heat pump with three 80 m (262 ft) ground boreholes and "central" controlled residential ventilation systems in each unit.
Actual consumption: approximately 8,200 kWh per year including central domestic hot water production.
At the time, I created a very detailed heating demand calculation (9,200 kWh/year). Considering factors like building time constant and solar and internal (people/devices) heat gains, the actual heating demand is further reduced compared to the calculation. These effects are usually not considered in superficial calculations. According to the calculation, a 9 kW heat pump would have sufficed, but the heating engineer refused and installed only a 12 kW unit.
You are planning for 14 occupants at full occupancy. During peak times, such as when all working residents want to shower in the morning simultaneously, the 12 kW heat pump may possibly reach its limits. This depends on the chosen domestic hot water system. In the above-mentioned multi-family house, a 1,000 L (265 US gallons) hygienic buffer tank with stainless steel corrugated pipe is used, and there have been no complaints so far with 8 occupants.
With 14 occupants, it would be worth considering a larger buffer tank and/or a bigger heat pump (1,200–1,500 L [317–396 US gallons], 16 kW). Another approach would be individual electric instantaneous water heaters (potentially supported by photovoltaic-powered electricity) in the residential units – this also avoids the issue of legionella.
From my own difficult experience, heating engineers tend to recommend oversized heat pumps. The reason is simple: it heats quickly and reliably, design flaws are easily covered up, and the customer only realizes much later that this results in a lower overall efficiency with frequently cycling heat pumps.
An experience value from a multi-family house with the following key data:
Multi-family house, 475 m² (5115 ft²) with 4 residential units and 8 occupants:
Some building component values:
Wall 0.15 W/m²K
Windows 0.75 W/m²K
Roof 0.11 W/m²K
The final energy consumption of the multi-family house is 15.8 kWh/(m²*a). The house has a relatively large window area of about 170 m² (1830 ft²).
Heating is provided by a 12 kW ground-source heat pump with three 80 m (262 ft) ground boreholes and "central" controlled residential ventilation systems in each unit.
Actual consumption: approximately 8,200 kWh per year including central domestic hot water production.
At the time, I created a very detailed heating demand calculation (9,200 kWh/year). Considering factors like building time constant and solar and internal (people/devices) heat gains, the actual heating demand is further reduced compared to the calculation. These effects are usually not considered in superficial calculations. According to the calculation, a 9 kW heat pump would have sufficed, but the heating engineer refused and installed only a 12 kW unit.
You are planning for 14 occupants at full occupancy. During peak times, such as when all working residents want to shower in the morning simultaneously, the 12 kW heat pump may possibly reach its limits. This depends on the chosen domestic hot water system. In the above-mentioned multi-family house, a 1,000 L (265 US gallons) hygienic buffer tank with stainless steel corrugated pipe is used, and there have been no complaints so far with 8 occupants.
With 14 occupants, it would be worth considering a larger buffer tank and/or a bigger heat pump (1,200–1,500 L [317–396 US gallons], 16 kW). Another approach would be individual electric instantaneous water heaters (potentially supported by photovoltaic-powered electricity) in the residential units – this also avoids the issue of legionella.
B
Bausparfuchs1 May 2023 22:40I myself rent out 10 apartments with a total area of 500 sqm (5400 sq ft). Politically, private small landlords are basically dead. The fewer apartments you rent out, the greater your risk becomes.
As a private landlord, you are legally vulnerable with almost no rights. There are organizations like tenants' associations offering free lawyers who will scrutinize every utility bill down to the smallest detail. Even if you have these bills prepared by a company, not all of the billing costs can be passed on to tenants.
Therefore, I can only advise you to shift the cost risks onto the tenants. For 4 apartments, I would install a small heat pump with a hot water storage tank in each unit. These already exist, similar to gas-fired individual heating systems. This way, it’s connected to the tenant’s electricity meter, and they have to pay. You save yourself the complicated heating cost billing, which has become extremely complex and is always subject to dispute when heating is centralized.
A judge at the local court once told me that it has become impossible today to create legally secure utility or heating cost statements. And as a landlord, you are even supposed to bear part of your tenants’ CO₂ charges. This way, you avoid that.
The electricity provider can disconnect the power to the tenant’s heat pump. Of course, you are not allowed to do that yourself. And if you have centralized heating, it is technically difficult to separate consumption for individual tenants.
In the end, there is always the question of whether tenants can and will continue to pay rising energy prices. Ultimately, the landlord is stuck with the costs.
I have already paid off my rental property, so I no longer have to make loan payments. But if I still had mortgage obligations, I probably wouldn’t sleep well at night. I expect, at minimum, that property tax will no longer be allowed to be passed on to the rent and that it will rise significantly. Then they will cap the recoverable heating costs or come up with other tricks to make the “bad landlords” pay. So, I just want to warn you a bit.
Renting out property in Germany has become a tough business. The money doesn’t simply come in by mail. For that reason, I admire people like you. I wonder how anyone can still rent reasonably with construction costs exceeding 3000 euros per sqm (280 sq ft).
With 500 sqm (5400 sq ft) of rental space, including the land, the cost will be about 2 million euros. Probably even more. At 4 percent interest and 2 percent repayment, it would take me 28 years to pay off the property. The monthly payment would be 10,000 euros. Even under the best conditions, I would need to charge 20 euros per sqm in rent, which is unrealistic. Now, fact-checkers, please explain to me why I should take that risk?
As we are currently seeing, the plan to build 400,000 new apartments every year is looking bleak. That probably won’t happen.
As a private landlord, you are legally vulnerable with almost no rights. There are organizations like tenants' associations offering free lawyers who will scrutinize every utility bill down to the smallest detail. Even if you have these bills prepared by a company, not all of the billing costs can be passed on to tenants.
Therefore, I can only advise you to shift the cost risks onto the tenants. For 4 apartments, I would install a small heat pump with a hot water storage tank in each unit. These already exist, similar to gas-fired individual heating systems. This way, it’s connected to the tenant’s electricity meter, and they have to pay. You save yourself the complicated heating cost billing, which has become extremely complex and is always subject to dispute when heating is centralized.
A judge at the local court once told me that it has become impossible today to create legally secure utility or heating cost statements. And as a landlord, you are even supposed to bear part of your tenants’ CO₂ charges. This way, you avoid that.
The electricity provider can disconnect the power to the tenant’s heat pump. Of course, you are not allowed to do that yourself. And if you have centralized heating, it is technically difficult to separate consumption for individual tenants.
In the end, there is always the question of whether tenants can and will continue to pay rising energy prices. Ultimately, the landlord is stuck with the costs.
I have already paid off my rental property, so I no longer have to make loan payments. But if I still had mortgage obligations, I probably wouldn’t sleep well at night. I expect, at minimum, that property tax will no longer be allowed to be passed on to the rent and that it will rise significantly. Then they will cap the recoverable heating costs or come up with other tricks to make the “bad landlords” pay. So, I just want to warn you a bit.
Renting out property in Germany has become a tough business. The money doesn’t simply come in by mail. For that reason, I admire people like you. I wonder how anyone can still rent reasonably with construction costs exceeding 3000 euros per sqm (280 sq ft).
With 500 sqm (5400 sq ft) of rental space, including the land, the cost will be about 2 million euros. Probably even more. At 4 percent interest and 2 percent repayment, it would take me 28 years to pay off the property. The monthly payment would be 10,000 euros. Even under the best conditions, I would need to charge 20 euros per sqm in rent, which is unrealistic. Now, fact-checkers, please explain to me why I should take that risk?
As we are currently seeing, the plan to build 400,000 new apartments every year is looking bleak. That probably won’t happen.
Heat pumps, Google searches, and oil-based heating installers are a volatile combination that can end up causing a lot of trouble.
Input screen – Field 1: “Area”, Field 2: “Number of residential units”, Field 3: “Year built”?
Output: 30 kW.
There is no fixed heating demand for KfW standards or their energy classes, nor for the Building Energy Act 2020 (GEG 2020).
The allowable maximum yearly heating demand for new buildings must not exceed that of the respective reference building.
The reference building is a virtual house with the same volume and the same surface areas of building components (windows, roof, walls, floor) constructed with the valid standard components and a standard heating system according to the Building Energy Act 2020, with improved values according to KfW standards.
So you can build a 3 m (10 ft) wide, 20 m (66 ft) long narrow building with one story and a complete glass facade on the north side with very high heating demand and still comply with GEG 2020. Or you can build a cube with minimal windows, all facing south, meeting the building standard of the Building Energy Act 2020—with significantly lower heating demand.
The larger the house, the lower the heating demand per m² (square meter), unless it is a narrow building.
@BobRoss already explained how he solved it. Just as I suggested – calculate the heat load, size the heat pump and suitable buffer storage with fresh water module accordingly. You cannot apply a one-size-fits-all solution.
deri254 schrieb:According to the Building Energy Act 2020, the thermal insulation certificate is part of the building permit / planning permission application. Someone must have done some calculations. Whether these correspond to reality is another matter.
There is no thermal insulation certificate so far because I have done everything myself and without any funding applications I didn’t need one.
deri254 schrieb:The “bigger is better” approach has always been common with oil and gas boilers. 20% more capacity is usually no problem, costs about 10% more, but you hardly notice it during operation. Heat pumps, however, if oversized, also provide sufficient heat but tend to rapidly switch on and off frequently above 0°C (32°F) because they can’t modulate down far enough. It’s not just the nominal kW rating that matters here, but also the lower modulation limit at moderate outdoor temperatures (heat pumps usually don’t have their lowest output at higher temperatures between 0°C and 10°C (32°F and 50°F)). It isn’t necessarily harmful to choose one size bigger if the minimum modulation limit remains the same. Generally, however, no one needs more than 8 kW in a newly built single-family home—if that is the case, your domestic hot water tank is probably too small, or the rain shower and bathtub are running at the same time after the three kids come home from sports and have all taken a shower. That needs to be considered in the planning phase.
A friend chose a slightly larger system for his single-family house, also a bit extra for domestic hot water, because he says it often causes problems.
deri254 schrieb:I didn’t realize they are now doing HVAC system design as well.
My building materials supplier also entered this into his software and suggested 30 kW.
Input screen – Field 1: “Area”, Field 2: “Number of residential units”, Field 3: “Year built”?
Output: 30 kW.
deri254 schrieb:I don’t know. Keywords: room-by-room heat load calculation and domestic hot water demand calculation. Software: Hottgentroth, BKI Energieplaner, or others.
Is 14 kW really enough then? And which one would you recommend?
deri254 schrieb:Maybe ChatGPT knows more.
Heating demand according to Google on several platforms:
There is no fixed heating demand for KfW standards or their energy classes, nor for the Building Energy Act 2020 (GEG 2020).
The allowable maximum yearly heating demand for new buildings must not exceed that of the respective reference building.
The reference building is a virtual house with the same volume and the same surface areas of building components (windows, roof, walls, floor) constructed with the valid standard components and a standard heating system according to the Building Energy Act 2020, with improved values according to KfW standards.
So you can build a 3 m (10 ft) wide, 20 m (66 ft) long narrow building with one story and a complete glass facade on the north side with very high heating demand and still comply with GEG 2020. Or you can build a cube with minimal windows, all facing south, meeting the building standard of the Building Energy Act 2020—with significantly lower heating demand.
The larger the house, the lower the heating demand per m² (square meter), unless it is a narrow building.
deri254 schrieb:Where does that come from? Flat rate? Why? It doesn’t make sense. If the heating load is greater than the peak load needed for the buffer tank / hot water storage and the heat load calculation already includes standby times for heat pump tariffs and domestic hot water preparation, you don’t need a surcharge for hot water. If you do, then increase the storage size.
A 20% surcharge for domestic hot water then results in about 22 kW.
deri254 schrieb:Oil/gas heating is a completely different story in terms of sizing because oversizing by 100% isn’t a big deal there.
My heating installer friend once roughly estimated a 24 kW boiler for oil or gas with my data.
Bausparfuchs schrieb:I can’t comment much on the hate speech, but the suggestion is actually not bad, especially if no separate HVAC planning is to be done. The problem here is that the smallest heat pumps on the market usually have a nominal output of 5 kW and a minimum output of about 2 kW and are all too large because the heating load of each individual apartment is too low.
For 4 apartments, I would install a small heat pump with domestic hot water heat storage in each unit.
@BobRoss already explained how he solved it. Just as I suggested – calculate the heat load, size the heat pump and suitable buffer storage with fresh water module accordingly. You cannot apply a one-size-fits-all solution.
The building application along with the planning was already prepared and submitted by myself in 2019. At that time, a thermal insulation certificate (a rather vague requirement) was not yet necessary, at least not in our area.
These are very detailed explanations, but what I am mainly interested in is which heat pump manufacturer and model could be used for the multi-family house without any concerns regarding price/performance/guarantee, even without subsidies (so that I don’t have to worry or have doubts compared to well-known brands about it failing). This is important to me because I want to avoid costs being (much) higher than for an oil or gas heating system, for which I would also need a chimney that would add approximately 2500-3000 euros in additional expenses.
These are very detailed explanations, but what I am mainly interested in is which heat pump manufacturer and model could be used for the multi-family house without any concerns regarding price/performance/guarantee, even without subsidies (so that I don’t have to worry or have doubts compared to well-known brands about it failing). This is important to me because I want to avoid costs being (much) higher than for an oil or gas heating system, for which I would also need a chimney that would add approximately 2500-3000 euros in additional expenses.
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