ᐅ Single-family house with KfW55 / mechanical ventilation with heat recovery or complying with Energy Saving Ordinance standard – experiences and opinions?

Hello everyone,

First of all, I want to say that this forum has already provided me with many helpful suggestions and opinions. It’s really impressive to see the knowledge and engagement here!

In our case, the building permit / planning permission (with KfW 55 standard and controlled residential ventilation) was approved last week, and we have two remaining solid house providers to choose from, so we will decide shortly whom to go with for our construction project (typical single-family house, pitched roof, gas condensing boiler, interior and exterior walls made of sand-lime brick, about 190 sqm (2045 sq ft), construction costs around 460k plus additional costs).

We only have one open question left: so far, we were fully focused on KfW 55 with controlled residential ventilation — but now, shortly before finalizing, some doubts have arisen. The arguments we hear against KfW 55 and in favor of just following the energy saving ordinance (EnEV) are, for example:

- “Not worth it,” meaning the additional construction costs and KfW loan or repayment bonus are disproportionate for KfW 55; “better to build without KfW support in the current interest rate environment, it ends up the same.”

- “Noise from the controlled ventilation system,” meaning KfW 55 requires installing a ventilation system that could cause disturbing noise (we are subjectively very sensitive to noise). And the controlled ventilation is not necessary, “with reasonable airing behavior, it works without it, it’s cheaper and actually better for indoor air quality.”

- “The energy saving ordinance standard is sufficient with proper wall construction and decent windows; the slight additional energy savings aren’t worth the extra effort and potentially adding a noise source. Today’s homes built to the EnEV standard already have very low energy costs.”

- “You don’t need KfW 55 because you plan to live in the house permanently. If you wanted to sell again, KfW 55 would be more important.”

You might notice we are a bit unsure whether to stick to our KfW 55 plan or rather “downgrade” to the energy saving ordinance standard.

We would really appreciate your opinions, comments, advice, etc., as we want to finalize the deal with the general contractor this weekend.

Many thanks for your feedback and happy Halloween!

Mertha

How long have you been in the planning phase? I find it a bit surprising that you see KfW 55 as automatically linked to mechanical ventilation with heat recovery. It’s not necessary at all if the planning and calculations are done correctly—for example, not just using general assumptions about thermal bridges.

I am building with mechanical ventilation with heat recovery and wouldn’t do it without, regardless of KfW standards or energy-saving regulations.

Did you notice that KfW subsidies were increased to €18,000 (about $18,000) in 2020? There is a lot of technology available for just under €20,000 (about $20,000).

I see no reason to forgo KfW 55 standards if you need financing. The small extra effort is compensated by the subsidies. Additionally, you end up with a higher-quality house, which is beneficial for the future.

Everything about controlled residential ventilation has already been said by @OWLer. Never again without it, no matter the type of house.

Of course, you can also live comfortably in a house built to energy-saving regulations. But better is the enemy of good.

Phew, once again the topic of controlled residential ventilation or not.

I’d say that after moving in with my wife, we didn’t manage to ventilate regularly. It was a two-room apartment on the ground floor, I worked shifts, so the bedroom window was closed for at least 12 hours. Then drying laundry in the living room, pets bringing in mice, and so on. The result was mold on the wall.

For us, the comfort of not having to open dozens of windows every day was worth the money.

OWLer schrieb:

How long have you been in the planning phase? I find it a bit surprising that you see KFW55 as automatically linked to mechanical ventilation with heat recovery. It’s not necessary at all if the planning and calculations are done correctly – for example, not just using generalized thermal bridge values and so on.

I am building with mechanical ventilation with heat recovery and wouldn’t do it without, regardless of KFW or the Energy Saving Ordinance.

Are you aware that KFW subsidies were increased to €18,000 (about $18,000) in 2020? You get quite a bit of technology for just under €20,000.

Thanks! But what exactly does “not just using generalized thermal bridge values” mean in this context? And yes, we are aware of the €18,000 (about $18,000). Best regards, Mertha

tomtom79 schrieb:

Phew, here we go again with the topic of mechanical ventilation or not.

I’ll put it this way: after moving in with my wife, we couldn’t manage to ventilate regularly. We lived in a two-room apartment on the ground floor. I worked shifts, so the bedroom window was closed for at least 12 hours. Meanwhile, laundry was drying in the living room, we had pets to take care of, and so on. The result was mold on the wall.

For us, the convenience of not having to open dozens of windows every day was worth the cost.

Hi Tomtom79, thanks for your reply. Sorry if I’m bringing up this topic for the umpteenth time. I couldn’t find anything quite specific to “my” issue in the search.

Are there any current-generation products with experience regarding particularly quiet mechanical ventilation systems? I’m doing some more research here in the forum since I haven’t looked into that yet.

Best regards, Mertha