ᐅ Which heating system is suitable for a newly built KfW 70 house?
Created on: 5 Aug 2013 23:08
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deus77We are planning to build a new KfW 70 house and are unsure which heating system to install.
Basic parameters:
Living area 150 sqm (1600 sq ft)
Single-story, underfloor heating, electric shutters
Concept:
To be independent from gas or oil, we want to use an air-source heat pump (ground-source heat is significantly more expensive), combined with solar thermal panels of about 6 sqm (65 sq ft) optimally facing south. Additionally, we are considering a water-connected wood stove to be able to heat with wood as a backup if necessary. Possibly, we will also install solar panels facing west to generate electricity (for the air-source heat pump and general self-consumption).
Of course, the initial costs are quite substantial. With a “normal” calculation from today’s point in time, it will take many years for the investment to pay off. If a loan is taken for this and repaid little by little (with interest!), it becomes more complex. However, we believe that raw material prices for gas and oil will rise significantly over the next years. Electricity prices too, which is why we consider the additional solar panels for self-consumption. Fortunately, due to an inheritance, we have enough cash to pay for the entire project upfront (no loan!). However, nobody has been able to provide us with a suitable cost-benefit analysis so far. Does this make sense, or are we getting carried away?
A builder friend advises us to install a good gas heating system with solar thermal panels. The house is very well insulated, so that should be sufficient. Plus a simple wood stove, and that’s about it...
I would appreciate hearing a few opinions here… The project might start this year.
Thank you and best regards
Tom
Basic parameters:
Living area 150 sqm (1600 sq ft)
Single-story, underfloor heating, electric shutters
Concept:
To be independent from gas or oil, we want to use an air-source heat pump (ground-source heat is significantly more expensive), combined with solar thermal panels of about 6 sqm (65 sq ft) optimally facing south. Additionally, we are considering a water-connected wood stove to be able to heat with wood as a backup if necessary. Possibly, we will also install solar panels facing west to generate electricity (for the air-source heat pump and general self-consumption).
Of course, the initial costs are quite substantial. With a “normal” calculation from today’s point in time, it will take many years for the investment to pay off. If a loan is taken for this and repaid little by little (with interest!), it becomes more complex. However, we believe that raw material prices for gas and oil will rise significantly over the next years. Electricity prices too, which is why we consider the additional solar panels for self-consumption. Fortunately, due to an inheritance, we have enough cash to pay for the entire project upfront (no loan!). However, nobody has been able to provide us with a suitable cost-benefit analysis so far. Does this make sense, or are we getting carried away?
A builder friend advises us to install a good gas heating system with solar thermal panels. The house is very well insulated, so that should be sufficient. Plus a simple wood stove, and that’s about it...
I would appreciate hearing a few opinions here… The project might start this year.
Thank you and best regards
Tom
I
Irgendwoabaier5 Aug 2013 23:42There are already quite a few questions and answers here about all the heating points.
Fireplace with water jacket? The control system will definitely appreciate that, as it needs to absorb some of the fireplace’s heat output and store it in the buffer tank.
Solar thermal? Some people believe it can really pay off—if you can install a large, fully insulated buffer tank in the basement. Probably not practical in combination with an air-to-water heat pump.
Now add a central mechanical ventilation system with heat recovery—and the control systems will be happy.
Recommendations around here:
Recommendation 1: Gas condensing boiler + solar thermal.
Recommendation 2: Air-to-water heat pump + photovoltaic system for self-consumption.
The better the building envelope is insulated, the more likely an air-to-water heat pump makes sense. Even more so with a proper ventilation system.
Depends who you ask. The better insulated the house, the more an air-to-water heat pump makes sense.
Ground-source heat pump: depends on the size of the property whether it’s feasible or not. For the house I currently live in, it’s hopeless. For the one I’m building, it might be possible but calculations are still underway...
Best regards,
GrrIngo
Fireplace with water jacket? The control system will definitely appreciate that, as it needs to absorb some of the fireplace’s heat output and store it in the buffer tank.
Solar thermal? Some people believe it can really pay off—if you can install a large, fully insulated buffer tank in the basement. Probably not practical in combination with an air-to-water heat pump.
Now add a central mechanical ventilation system with heat recovery—and the control systems will be happy.
Recommendations around here:
Recommendation 1: Gas condensing boiler + solar thermal.
Recommendation 2: Air-to-water heat pump + photovoltaic system for self-consumption.
The better the building envelope is insulated, the more likely an air-to-water heat pump makes sense. Even more so with a proper ventilation system.
Depends who you ask. The better insulated the house, the more an air-to-water heat pump makes sense.
Ground-source heat pump: depends on the size of the property whether it’s feasible or not. For the house I currently live in, it’s hopeless. For the one I’m building, it might be possible but calculations are still underway...
Best regards,
GrrIngo
Another idea: why limit yourself to KfW70 standard and not aim for better insulation closer to Passive House levels?
Our approach for a similar house (detached single-family home, 160 sqm (approximately 1,722 sq ft) living area, 1.5 stories, no basement, underfloor heating, ideal south-facing orientation with large south-facing windows) looks like this:
- Exterior walls made of Poroton T7 with integrated mineral wool insulation, 49 cm (19 inches) thick. You can find more info online.
- Gas condensing boiler, 6 kW (6.6 hp) for hot water and heating
- No solar thermal system due to high costs including planning, installation, storage tank, piping, controls, etc., amounting to around 15,000 euros, which won’t pay off with the low heating demand of the house. Thanks to the 15% rule relating to the well-insulated exterior walls, you still qualify for KfW funding.
- No central mechanical ventilation with heat recovery because it is similarly expensive as a solar thermal system. Instead, we install a so-called “moisture-regulated ventilation system” (just look it up). The slightly increased heating demand due to intake of non-preheated air in winter is roughly equivalent to or even less than the operating costs of a central mechanical ventilation with heat recovery.
- No heat pump system. Very costly to install (over 15,000 euros) and may only pay off after 20 years—by which time the pump will probably need replacing anyway. Personally, I also dislike the noisy, unattractive outdoor units, and in my opinion, the annual performance factor considered good locally is far too low. There has been significant lobbying on this topic.
- Leave space in the basement or utility room for future upgrades to technologies such as solar thermal, photovoltaic, heat pumps, etc. There is a lot of development in this area; in 20 to 30 years, it might become worthwhile to install these systems.
So we invest a bit more money upfront in high-quality insulation. It is durable, has no operating costs, and reduces dependence on gas price fluctuations.
Best regards
rw
Our approach for a similar house (detached single-family home, 160 sqm (approximately 1,722 sq ft) living area, 1.5 stories, no basement, underfloor heating, ideal south-facing orientation with large south-facing windows) looks like this:
- Exterior walls made of Poroton T7 with integrated mineral wool insulation, 49 cm (19 inches) thick. You can find more info online.
- Gas condensing boiler, 6 kW (6.6 hp) for hot water and heating
- No solar thermal system due to high costs including planning, installation, storage tank, piping, controls, etc., amounting to around 15,000 euros, which won’t pay off with the low heating demand of the house. Thanks to the 15% rule relating to the well-insulated exterior walls, you still qualify for KfW funding.
- No central mechanical ventilation with heat recovery because it is similarly expensive as a solar thermal system. Instead, we install a so-called “moisture-regulated ventilation system” (just look it up). The slightly increased heating demand due to intake of non-preheated air in winter is roughly equivalent to or even less than the operating costs of a central mechanical ventilation with heat recovery.
- No heat pump system. Very costly to install (over 15,000 euros) and may only pay off after 20 years—by which time the pump will probably need replacing anyway. Personally, I also dislike the noisy, unattractive outdoor units, and in my opinion, the annual performance factor considered good locally is far too low. There has been significant lobbying on this topic.
- Leave space in the basement or utility room for future upgrades to technologies such as solar thermal, photovoltaic, heat pumps, etc. There is a lot of development in this area; in 20 to 30 years, it might become worthwhile to install these systems.
So we invest a bit more money upfront in high-quality insulation. It is durable, has no operating costs, and reduces dependence on gas price fluctuations.
Best regards
rw
Hello,
If you want to evaluate the investment or cost-effectiveness of technical solutions, you first need to know the actual demand (capacity, energy) for heating, hot water, and possibly ventilation. Everything else is speculation or looking into a very cloudy crystal ball (clairvoyance)!
Generally: The higher the demand, the greater the investment, and the higher the expectations for energy efficiency. It also makes sense to use free environmental energy whenever possible.
Best regards.
deus77 schrieb:Similar questions have been asked here quite often. Just browse through the forum for more information!
We are planning to build a new KfW 70 house and don’t know which heating system to install....
deus77 schrieb:Investments in the thermal quality of the building envelope and in building systems are essentially a substitution for future energy costs. Interest rates are historically low, and no one knows how the cost per kWh for each energy source will develop. However, it is certain that they will rise, usually well above the general inflation rate.
...Of course, the initial costs are quite significant. With a “normal” calculation from today’s date X onwards, it takes many years for everything to pay off.
If you want to evaluate the investment or cost-effectiveness of technical solutions, you first need to know the actual demand (capacity, energy) for heating, hot water, and possibly ventilation. Everything else is speculation or looking into a very cloudy crystal ball (clairvoyance)!
Generally: The higher the demand, the greater the investment, and the higher the expectations for energy efficiency. It also makes sense to use free environmental energy whenever possible.
deus77 schrieb:Whether that really is a friend, I would doubt ;-)
...A builder friend recommends installing a good gas heating system with solar thermal.
Best regards.
Hello,
Considering the current energy prices, most comparisons show that over a period of 20-25 years, the total costs for gas, wood, and heat pumps tend to be quite similar due to the different investment and operating expenses. Only oil heating is usually estimated to have higher overall costs. Therefore, the key question here is whether you prioritize lower initial costs or lower operating costs.
This is where the more complex assessment of each individual case begins. The efficiency of solar thermal systems, which can be used in combination with a gas condensing boiler or an air-source heat pump, as well as that of solar panels for electricity generation, depends heavily on location and shading. Similarly, the performance of an air-source heat pump is also influenced by the location.
I would definitely recommend having a calculation done for the calorific value and heating demand and then creating a corresponding cost comparison. This does cost a bit, but investing a little more in the planning phase is rarely a mistake.
After that, I would conduct the overall cost comparison over 20-25 years mentioned before. If significant differences appear here, you will have a solid basis for your decision. If the results are as close as they often are, you should then consider whether, for reasons other than cost (e.g., storage space, personal effort to operate the system, noise, size of the installation, maintenance requirements, future adaptability, ecological concerns, and more), you prefer one heating system over another.
In this context, the proposed gas condensing boiler combined with solar thermal can certainly score points due to easy supply, low space requirements, no additional storage space needed, and virtually no personal effort for operation.
Best regards
Erik
Considering the current energy prices, most comparisons show that over a period of 20-25 years, the total costs for gas, wood, and heat pumps tend to be quite similar due to the different investment and operating expenses. Only oil heating is usually estimated to have higher overall costs. Therefore, the key question here is whether you prioritize lower initial costs or lower operating costs.
This is where the more complex assessment of each individual case begins. The efficiency of solar thermal systems, which can be used in combination with a gas condensing boiler or an air-source heat pump, as well as that of solar panels for electricity generation, depends heavily on location and shading. Similarly, the performance of an air-source heat pump is also influenced by the location.
I would definitely recommend having a calculation done for the calorific value and heating demand and then creating a corresponding cost comparison. This does cost a bit, but investing a little more in the planning phase is rarely a mistake.
After that, I would conduct the overall cost comparison over 20-25 years mentioned before. If significant differences appear here, you will have a solid basis for your decision. If the results are as close as they often are, you should then consider whether, for reasons other than cost (e.g., storage space, personal effort to operate the system, noise, size of the installation, maintenance requirements, future adaptability, ecological concerns, and more), you prefer one heating system over another.
In this context, the proposed gas condensing boiler combined with solar thermal can certainly score points due to easy supply, low space requirements, no additional storage space needed, and virtually no personal effort for operation.
Best regards
Erik
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