ᐅ Heat Pump for New Single-Family Home Built to Energy Efficiency Standard 55

Hello dear forum members,

I am currently working with the company Lehner Haus from Heidenheim to build my prefabricated timber-frame house. During the plan review, the topic of which air-to-water heat pump to use came up. I tried to get some information beforehand, but I would still appreciate hearing your opinions.

First, a few details about the build itself. The plan is for an Efficiency House 55 with about 200 sqm (2,150 sq ft) of living space. I am attaching the plans as well. A floor heating system is planned for all rooms except the pantry and technical room. Four people will live in the house. I would describe our usage habits as normal or average. At the moment, nobody spends 30 minutes straight in the shower. The bathtub is currently used about every two weeks. Of course, this may change as my children get older. Temperature-wise, the bedroom is kept rather cool. The living room is around 20–21°C (68–70°F). The bathroom is naturally a bit warmer, and at least the upstairs bathroom will have a towel radiator.

Lehner Haus offers two heat pump providers: Vaillant and Viessmann. Currently, the price includes a Vaillant Arotherm Split 105/5 AS, a 300-liter (79 gallon) hot water storage tank, and a compact buffer tank VWZ MPS40. A complete heating load calculation is not yet available. However, a rough preliminary estimate by the company indicated that the heating system is oversized and that a 75/5 AS or 85/5 AS would likely be sufficient. They also recommended switching from the aroTherm Split to an aroTherm Plus. Lehner Haus’s current recommendation is a Vaillant aroTherm Plus 75/6 A S2.

Here, I am uncertain whether this will be sufficient, and I also wonder why a much larger heat pump was originally offered. In various online posts, I read that heat pumps are sometimes undersized, causing inefficient operation because they have to run at "high load." But I also see the opposite advice that heat pumps should not be planned too large. As a layperson, it is also difficult for me to compare which heat pump is better (Split or Plus). As far as I understand, the Plus model is more efficient and quieter. But is it worth the extra cost? And does Viessmann maybe offer comparable cheaper units or better models for the same price? Viessmann also won at Stiftung Warentest in the current issue. Of course, only Lehner Haus can tell me the final price.

Removing the heat pump from Lehner Haus’s scope of work is unfortunately not an option for me, since I would then have to exclude both the underfloor heating and the entire plumbing installation as well (it’s apparently the same team).

Could you possibly help me here and give recommendations on what the right choice is? I need to make a final decision at the beginning of November.

Many thanks,
Best regards,
ToBu1991