ᐅ Alternative to the Weishaupt WWP LS 8 (Rotex, Kermi, etc.)?

Hello everyone,

I am currently looking for a suitable air-to-water heat pump for our single-family house. Here are some key details:
- 200 sqm (2,150 sq ft)
- Underfloor heating
- Bonded parquet flooring
- Heating load: 7.6 kW
- Household of 4 people
- Current planned supply temperature: 35°C (95°F), target 30°C (86°F)

The heating installer is currently recommending the Weishaupt WWP LS 8 (split unit). Weishaupt also offers the monoblock WWP LA 9, but it does not have inverter technology, and the new WWP LB (bi-block). However, the bi-block requires too much space in the utility room, so it is not an option.

The LS 8 is not particularly quiet and only has 200 liters (53 gallons) of hot water storage and a 100-liter (26 gallons) buffer tank. So it is somewhat less than ideal. Therefore, I am looking for an alternative. The installer suggested a Kermi as an option, although those units are more expensive. In my opinion, a more affordable alternative might be the Rotex Compact "Ultra". It has no buffer tank but can use the domestic hot water cylinder as a buffer if necessary.

If I understand correctly, the Kermi and Rotex units are similar, with Kermi being the higher quality option. The question now is whether the Rotex is sufficient or if it would be better to go with Kermi. Or should I stick with Weishaupt or consider a completely different brand?

What are your experiences or opinions?

Brand doesn’t really matter, they all boil water. Choose the one your heating engineer is familiar with. We have a Novelan inverter, which is extremely quiet, and so far we are satisfied. I can’t comment on durability, as it is only a few years old.

You don’t just buy any car simply because they all run on fuel and get you from point A to point B. I have often read that heating technicians frequently install air-to-water heat pumps incorrectly. It only takes them hiring a new employee who isn’t yet familiar with the system. Especially since the manufacturer handles the commissioning. Considering that an air-to-water heat pump can cost 10,000–15,000 euros (approximately 11,000–16,500 USD) and operating costs depend on it, I don’t want to simply go with whatever the heating contractor recommends.

More important than the brand is the overall planning. Keywords for research: room-by-room heating load calculation with the design of the underfloor heating for the lowest possible supply temperature (e.g., <30°C (86°F)), keeping all circuits around 80 meters (260 feet) long, installing plenty of surface heating in the bathroom, and no buffer tank. Leave out the bypass valve (ERR) from the start or later. The heating installer will not implement these points in your best interest, so take the planning into your own hands.

The unit itself should not be oversized but must be modulating. A compact unit is easier to replace and may not require the annually mandated climate service.

Is the heating load relatively high, or is the calculation correct? If you can reduce it to around 5 kW, you can go for the popular 5 kW heat pump from Panasonic (around €3,000 [3,000 Euros] if bought directly), and then invest savings into other measures: better insulation or a ventilation system to achieve the 5 kW target.

To continue the unfortunate car comparison: a buffer tank and ERR are roughly like buying a great car, but then retrofitting it with a single-speed automatic transmission and hiring a poor driver whose contract requires them to always get you from A to B on time.

Switching to an even better car then only brings minimal improvement.

@boxandroof, yes, I am aware that planning is important. I already mentioned that the heating engineer plans with a supply temperature of 35°C (95°F), but we would prefer a maximum of 30°C (86°F). The offered air-to-water heat pump includes a storage tank, and since we do not want an expansion vessel, the provided pumps are not of interest. I should have been clearer that I am aware of these points in the planning stage and that this is really just about the air-to-water heat pump. Nevertheless, thank you very much for the advice, as these aspects are often crucial for the heating system.

We will not get the heating load below 5 kW. We are already planning with a controlled mechanical ventilation system (currently Zehnder), but our area is 200 m² (2,150 sq ft) with a room temperature of 22°C (72°F) (yes, I know that is quite high).

I believe that the Rotex system does not require refrigerant maintenance. Rotex uses the new refrigerant and I also think it has less than 5 kg (11 lbs). However, that should not be the deciding factor now. Generally, I am moving away from Weishaupt, and Rotex has very good references. The heating installer suggested Kermi as an alternative, but I find very little information about it. Also, manufacturers generally do not provide consumer-friendly information. Of course, it is clear that all are highly efficient, SmartGrid capable, and controllable via smartphone.

It is somewhat difficult to compare Rotex with Kermi, for example. Tecalor is supposed to be good as well, but until a few weeks ago I was not familiar with any of these brands. Most people tend to think of Viessmann, Vaillant, Nibe, etc.