ᐅ Expert Assessment of Underfloor Heating in a Single-Family Home

Hello to the experts,

we are currently caught between two opinions and would therefore appreciate an independent assessment.

On one side, the heating specialist we hired (offering a complete package for our prefab house), and on the other, a close acquaintance who is also a technician/heating installer (and a perfectionist in his field).

We are building a prefab house with underfloor heating. The heating system is a gas condensing boiler from Viessmann (Vitodens 200W, nominal heat output 2.4-13 kW, calculated heating load is sufficient) plus a 300-liter (79 gallons) solar storage tank. There is a solar system with a collector area of 5 m² (54 ft²) (Viessmann Vitosol 200F) to support hot water production. The underfloor heating is installed using plastic piping made of PE-Xa/PAM. We have two heating circuits (1x ground floor, 1x upper floor).

Now the issue — according to the quote, the heating specialist will not install a mixing circuit for the underfloor heating. When asked how the flow temperature regulation would be managed, the answer was that it is controlled via the boiler, which is apparently a common method. Additionally, there is a device to prevent overheating (I don’t remember the exact name). The design temperature is 35°C (95°F).

Our acquaintance insists that installing a mixing circuit is essential; otherwise, it would be shoddy and highly questionable. Also, there is no backflow preventer (system separator BA) installed; no explanation was given for this.

We find it difficult to evaluate the situation. Is it really possible to operate without a mixing circuit? Is this standard practice or rather a cost-saving measure that may lead to poor workmanship? Or do we need to accept the additional cost and discussion and insist on installing a mixing circuit? What advantages would this give us?

Another questionable point: we received an offer for closer spacing of the heating loops including enlargement of the heating circuits (possibly to prepare for a future heat pump). The reasoning was that this only applies as an option with the Vitodens 200 model. If we were to choose the 300W instead (still undecided), it would not be necessary. Why is that? So far no one has been able to explain this convincingly.

Thank you very much for objective professional opinions.

Best regards,
Charly

Hello

The mixing circuit is only necessary if the heat generator, due to its design, cannot operate at such low temperatures or if multiple heating circuits with different temperature levels are used.

Neither applies in your case, as you have a condensing boiler and only one heating circuit.

Olli

@CharlyC42
It's good that Olli replied.
I wouldn't have known myself. Still, I wanted to say something about this question:
During any construction project, you can have such questions in every trade when craftsmen want to make sure or are used to doing things differently.
Often, this is because more experienced craftsmen learned with older technology and may follow a more conservative approach. Modern methods or regulations, such as energy saving requirements, are sometimes reluctantly accepted.
However, of course, any question about this is justified—we are not professional tradespeople after all 😉

Best regards, Yvonne

ypg schrieb:
You can have such a question in any trade during the course of a construction project,

Indeed! There is almost always a relative, acquaintance, or colleague who claims to know exactly what is right, and, of course, with your house build it turns out differently. Then you are left confused; one person says one thing, another says something else, and the layperson has no idea which option is actually correct or better.

In my opinion, this reflects the fact that contractors often receive little trust. In the example given, there were even two expert opinions that contradicted each other.

Thanks for the feedback. I’m certainly open to new ideas, but sometimes a conservative approach isn’t necessarily a bad thing, especially since many things from the past weren’t actually bad.
I think the heating system and underfloor heating play a crucial role because once installed, you can’t change what’s been built in. I would be very frustrated if I constantly had issues with the heating or its controls just because I tried to save money on an essential component.
So far, I’m not fully convinced by the arguments that modern condensing boilers regulate the flow temperature automatically, and no one has been able to explain this to me in detail yet. Is there anyone here in the forum who can clarify this?

Best regards,
Charly

Hello joedreck,
thank you very much for the plausible explanation!
The closer installation spacing is partly for a comfortable temperature and partly for future proofing, possibly for a heat pump. If this results in potential savings, I am glad.
Okay, I now understand the principle. If we install a mixing valve, would this change the balance again or possibly help to fine-tune the heating system?
In our current rental apartment, we also have underfloor heating, and it is very poorly installed and adjusted, causing us only problems. That is why I have doubts and want to find the optimal solution for the heating system in our house.