ᐅ Which type of heating system is recommended for a KfW 55 energy-efficient house?
Created on: 28 Aug 2011 21:12
A
amazingbeeA
amazingbee28 Aug 2011 21:12Hello! We are currently planning a house and, since this is not something you do often, we have many questions. Due to the development plan for our plot, we are required to build a KfW 55 energy efficiency house and are now unsure about what type of heating system we need. Builders have given us different advice!
Is it possible to install a standard gas condensing boiler combined with solar water heating, or do we have to use geothermal or air-source heat pumps?
I would appreciate any answers!
Is it possible to install a standard gas condensing boiler combined with solar water heating, or do we have to use geothermal or air-source heat pumps?
I would appreciate any answers!
B
Bauexperte29 Aug 2011 09:28Hello,
Please double-check that, because I really can’t imagine it; KfW 70, yes, that corresponds to today’s standard, but KfW 55? I’m also not sure the municipality is allowed to require that, unless you have chosen a plot in an area meant to serve as a flagship project.
What direction are you planning to go in, prefabricated or solid construction?
Best regards
amazingbee schrieb:
We are required to build a KfW 55 house due to the zoning plan of our plot.
Please double-check that, because I really can’t imagine it; KfW 70, yes, that corresponds to today’s standard, but KfW 55? I’m also not sure the municipality is allowed to require that, unless you have chosen a plot in an area meant to serve as a flagship project.
amazingbee schrieb:
Is it possible to install a standard gas condensing boiler combined with solar water heating, or do you have to use geothermal or air-source heat pumps?
What direction are you planning to go in, prefabricated or solid construction?
Best regards
A
amazingbee29 Aug 2011 14:23Hello building expert,
we actually HAVE to build to KfW 55 standard, but we knew that when we bought the plot. Well, now we’re dealing with various building companies, and one says we can achieve it with geothermal energy, another suggests an air heat exchanger, and others think a gas boiler will be enough since our building envelope is extremely airtight and well insulated. We want to build with solid construction (a prefab house is also fine) and are now unsure exactly how to meet this standard. It’s all quite expensive (additional insulation everywhere, different windows, ventilation system, etc.). So, what should we choose? Geothermal energy (only possible with deep drilling because the plot is too small) is costly. We feel like a deer caught in the headlights!
Best regards!
we actually HAVE to build to KfW 55 standard, but we knew that when we bought the plot. Well, now we’re dealing with various building companies, and one says we can achieve it with geothermal energy, another suggests an air heat exchanger, and others think a gas boiler will be enough since our building envelope is extremely airtight and well insulated. We want to build with solid construction (a prefab house is also fine) and are now unsure exactly how to meet this standard. It’s all quite expensive (additional insulation everywhere, different windows, ventilation system, etc.). So, what should we choose? Geothermal energy (only possible with deep drilling because the plot is too small) is costly. We feel like a deer caught in the headlights!
Best regards!
M
Micha&Dany24 Sep 2011 09:37Hello Amazingbee,
The topic of heating in a new build is difficult to answer, even for a KfW 55 house. In theory, you can meet the requirements with any heating system. It’s not just about the heating unit itself, but the overall package. The combination of heating, insulation, and so on must be right.
Unfortunately, many providers seem to make quite odd calculations, meaning many heating systems appear to be incorrectly sized...
In my opinion, the most important question to start with is: which energy source do you want to depend on in the long term? To heat your home, you need heating oil (which is nowadays unacceptable), gas, or electricity.
Next, you need to know your house’s heat energy demand. From this, you can calculate how much primary energy you need:
For example, with a heat pump having an annual performance factor of 4, you need 25W of electricity to produce 100W of heat.
Now you can already compare different heating systems based on their primary energy demand – which is probably crucial for the KfW calculation...
To decide on a heating system, you also need to consider your annual "fuel" costs (gas or electricity). It gets tricky when you try to estimate how prices will develop in the coming years.
In my opinion, the gas price will rise more sharply than the electricity price over the next years – meaning the operating costs of a gas system will probably be significantly higher compared to a heat pump. If you sum up the operating costs (including maintenance, chimney sweeps, etc.) over the heating system’s lifetime (usually calculated as 20 years) and add the initial investment costs (which are significantly higher for a heat pump than for a gas condensing boiler), it might be easier to make a decision.
Unfortunately, this calculation strongly depends on the future prices of electricity and gas – and no one can really predict that...
My personal opinion is that today – especially with a new build (even more so a KfW 55) – I would no longer opt for gas, but I could be wrong. We will see in 20 years.
I hope this helps you.
Best regards from the Ruhr area
Micha
The topic of heating in a new build is difficult to answer, even for a KfW 55 house. In theory, you can meet the requirements with any heating system. It’s not just about the heating unit itself, but the overall package. The combination of heating, insulation, and so on must be right.
Unfortunately, many providers seem to make quite odd calculations, meaning many heating systems appear to be incorrectly sized...
In my opinion, the most important question to start with is: which energy source do you want to depend on in the long term? To heat your home, you need heating oil (which is nowadays unacceptable), gas, or electricity.
Next, you need to know your house’s heat energy demand. From this, you can calculate how much primary energy you need:
For example, with a heat pump having an annual performance factor of 4, you need 25W of electricity to produce 100W of heat.
Now you can already compare different heating systems based on their primary energy demand – which is probably crucial for the KfW calculation...
To decide on a heating system, you also need to consider your annual "fuel" costs (gas or electricity). It gets tricky when you try to estimate how prices will develop in the coming years.
In my opinion, the gas price will rise more sharply than the electricity price over the next years – meaning the operating costs of a gas system will probably be significantly higher compared to a heat pump. If you sum up the operating costs (including maintenance, chimney sweeps, etc.) over the heating system’s lifetime (usually calculated as 20 years) and add the initial investment costs (which are significantly higher for a heat pump than for a gas condensing boiler), it might be easier to make a decision.
Unfortunately, this calculation strongly depends on the future prices of electricity and gas – and no one can really predict that...
My personal opinion is that today – especially with a new build (even more so a KfW 55) – I would no longer opt for gas, but I could be wrong. We will see in 20 years.
I hope this helps you.
Best regards from the Ruhr area
Micha
B
Bauexperte24 Sep 2011 14:26Hello,
Changing windows is nonsense – who told you that? If you want to build solid, you have to accept thicker masonry – 42.5 cm (17 inches) monolithic or 44.5 cm (18 inches) with external thermal insulation composite system (ETICS). However, this reduces the living area by roughly 6.0 cm (2 inches) or 8.0 cm (3 inches) on all floors. Usually, with the first brick size, you need to install more expensive technology, for example, an integrated system consisting of an air-to-water heat pump and controlled ventilation with heat recovery. The downside is that your utility room loses quite a bit of space, since these systems take up about 2.0 square meters (22 square feet) of wall space and protrude approximately 80 cm (31 inches) into the room. Typically, these systems cannot be installed in the basement unless the basement walls extend at least 1.0 m (3 feet) above ground level; the system must handle opposing supply and exhaust airflows.
For the second brick size, it strongly depends on the location of the plot. If it is favorable (few windows facing north, etc.), it might be possible that an air-to-water heat pump combined with decentralized ventilation can achieve the required standard. The structural engineer or building services planner should perform very precise calculations here.
Whatever your decision, KfW 55 means an additional cost for the building project of around €20,000-25,000 depending on house size for 42.5 cm masonry and €15,000-20,000 for 44.5 cm with ETICS, again depending on house size.
Kind regards
amazingbee schrieb:
Hello Bauexperte,
we REALLY HAVE to build to KfW 55 standard... We want to build with solid construction (a prefabricated house is also fine) and now we’re not exactly sure how to achieve this standard. It all gets quite expensive (extra insulation everywhere, different windows, ventilation system... etc). So, what should we choose? Geothermal energy (only possible with deep drilling because the plot is too small) is costly. We’re stuck now like a deer in headlights!
Changing windows is nonsense – who told you that? If you want to build solid, you have to accept thicker masonry – 42.5 cm (17 inches) monolithic or 44.5 cm (18 inches) with external thermal insulation composite system (ETICS). However, this reduces the living area by roughly 6.0 cm (2 inches) or 8.0 cm (3 inches) on all floors. Usually, with the first brick size, you need to install more expensive technology, for example, an integrated system consisting of an air-to-water heat pump and controlled ventilation with heat recovery. The downside is that your utility room loses quite a bit of space, since these systems take up about 2.0 square meters (22 square feet) of wall space and protrude approximately 80 cm (31 inches) into the room. Typically, these systems cannot be installed in the basement unless the basement walls extend at least 1.0 m (3 feet) above ground level; the system must handle opposing supply and exhaust airflows.
For the second brick size, it strongly depends on the location of the plot. If it is favorable (few windows facing north, etc.), it might be possible that an air-to-water heat pump combined with decentralized ventilation can achieve the required standard. The structural engineer or building services planner should perform very precise calculations here.
Whatever your decision, KfW 55 means an additional cost for the building project of around €20,000-25,000 depending on house size for 42.5 cm masonry and €15,000-20,000 for 44.5 cm with ETICS, again depending on house size.
Kind regards
Hello!
It is true that a KfW Efficiency House 55 involves more complex construction and higher investment costs. If the development plan requires this type of building, then you definitely have to invest the additional amount.
For those who do not necessarily need to build an efficiency house according to KfW standards, a good alternative is an energy-saving, well-insulated building envelope combined with simple heating technology (an affordable gas condensing boiler or an air-to-water heat pump) and an efficient mechanical ventilation system. The technical setup for a solar system usually does not pay off in the long term.
Best regards
T.H.
It is true that a KfW Efficiency House 55 involves more complex construction and higher investment costs. If the development plan requires this type of building, then you definitely have to invest the additional amount.
For those who do not necessarily need to build an efficiency house according to KfW standards, a good alternative is an energy-saving, well-insulated building envelope combined with simple heating technology (an affordable gas condensing boiler or an air-to-water heat pump) and an efficient mechanical ventilation system. The technical setup for a solar system usually does not pay off in the long term.
Best regards
T.H.
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