ᐅ KfW 55 or just the Energy Saving Regulation – Gas heating and minimal ventilation?

Hello dear forum members,

We will start building our house in September and have already signed a contract with the builder for a KFW 55 house with a central ventilation system and an air-source heat pump.

However, just the day before yesterday, the question arose again—after we realized that the kitchen extractor hood can only be installed as recirculation and not as exhaust due to the ventilation system and the negative pressure caused by an exhaust extractor hood—whether we should build a house more like in the past, meaning not so airtight that we would need a ventilation system, and use gas heating. Initially, this was our plan, but the sales representative at the builder advised against it. Since houses nowadays are so airtight, a ventilation system is necessary. That results in dry air, so additional measures are required. Also, the air-source heat pump is expensive, consumes a lot of electricity or makes you dependent on electricity prices, and with all its electronics, it is quite prone to malfunctions. If it breaks down, significant replacement costs are to be expected.

Yesterday, I spoke with the site manager at the builder about this issue. We discussed this question as well. He said that he would personally build his own house without ventilation and with gas or oil heating. Now the question is: Is this still allowed nowadays under the 2016 Energy Saving Ordinance (EnEV 2016), or will the requirements force me to build such an airtight house again that I would need a ventilation system? Then there is the question of whether I would really save anything overall by switching from the air-source heat pump to gas heating, since I would need an indoor chimney again.

Is it true that if I use gas, I definitely have to install solar thermal panels on the roof, or is there still the alternative of building the house more airtight (which of course would require ventilation again)?

Thank you in advance for your advice.

Best regards,
Sony

Hello,
KfW55 standard can be achieved without a ventilation system. This is a) a matter of comfort and b) requires careful consideration of whether your personal lifestyle fits this approach. Using a controlled ventilation system is definitely the safer choice, but if so, please use one with heat and humidity recovery.

An exhaust hood is also possible with KfW55 and controlled ventilation. Since the hood does not run continuously, the controlled ventilation must be paused while it is operating. This can be done using window contact switches, which means you have to open a window to run the hood. This makes sense, as the hoods move around 800 to 1000 m³ per hour (470 to 590 cubic feet per hour), and that air needs to come from somewhere.

Sony70 schrieb:
Thank you all in advance for your advice

It is best to get independent advice from an energy consultant (the person who prepares the energy performance calculation).

The assumption that a house built according to the Energy Saving Ordinance is less airtight than a KfW 55 house is incorrect.
The “issue” with the exhaust hood applies equally in both cases. You will need a window contact or a similar device to supply the necessary fresh air when the hood is in operation.

For comparison, a powerful exhaust hood moves five times more air at its highest setting than a ventilation system does during normal operation. Fresh air coming through the building envelope (“airtight house”) is therefore negligible.

Since you have already committed to a heat pump and ventilation system, switching to a different system will not make economic sense.

Domski schrieb:
An exhaust hood is also compatible with KfW55 standards and controlled residential ventilation. Since the hood does not run continuously, the controlled ventilation must be disabled during this time. This can be done using window contact switches, which means that a window must be opened to operate the hood.

I do not follow this conclusion: the same control signal can also be triggered by the hood being switched on.

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Hello, thank you very much in advance. What do you think about switching to GBWH plus controlled ventilation with heat recovery? (How much more would it cost to include humidity recovery?) Is it possible to achieve KfW 55 standard with this, or would we need the KfW Efficiency House standard? How does the cost comparison look? Currently, we have KfW 55 with an air-source heat pump and controlled ventilation. The house would remain the same, but we would need a chimney, and (in case we cannot meet the KfW 55 standard) we would not be eligible for the KfW loan nor the additional 5,000 EUR (2,000 USD) subsidy. Although the interest rates for both KfW and conventional home loans don’t differ much here. What is the overall cost implication? Another consideration is that if we switch to gas, we could also use the chimney for a wood stove and save approximately 2,000 EUR (2,000 USD) on an external chimney.

Do you think the builder would have any objections since we have already signed the contract with the above specifications?

Thank you very much in advance!