ᐅ Towel Radiators with Underfloor Heating – Do They Get Warm?

face26 schrieb:

I would question the "scheme" suggested by @Dogma.
My points are:

- The water heating coil for the mechanical ventilation with heat recovery is not really necessary; it is much less efficient than underfloor heating and involves additional investment costs that do not pay off.
- If I understood correctly, there is a hydraulic separator, but in the end the water from the underfloor heating still mixes with that of the radiator, which is not ideal since radiators can cause contamination.
- Even if it is not as critical for gas systems as for heat pumps, a 45°C (113°F) flow temperature is unnecessary, especially since underfloor heating does not require it in a house built to current energy-saving regulations. These higher temperatures seem to be maintained only because of the towel radiator.

If you are concerned that the bathroom won’t get warm enough, you just have to design it properly. If the room-specific heat load calculation shows that the bathroom does not reach the desired temperature at the given flow temperature, you should lay the pipes closer together and instead of installing a towel radiator, run a few more meters of pipe along the wall. In the end, this probably costs no more than the radiator plus the required hydraulic separator and avoids the mentioned disadvantages.

- I think you misunderstood something: the mechanical ventilation with heat recovery is not meant for heating. The coils only ensure that the incoming air is not too cold, nothing more. Whether there is a more energy-efficient solution, I don’t know, but I didn’t want electric heating elements in the mechanical ventilation, and I already had water-based heating.
- The towel radiator actually has its own separate circuit (e.g., with a hydraulic separator), but the separator does have a magnetic filter to at least prevent metal shavings from entering the underfloor heating system.
- Regarding the flow temperature, you seem to have misunderstood again: I said the gas boiler produces 45°C (113°F), not that the underfloor heating operates at 45°C. Please read carefully again.

Bookstar schrieb:

Forget about that with a heat pump. A 3-degree temperature difference is not possible. Anyone who wants that definitely needs an electric auxiliary heater. But I don’t understand why you would permanently need such a high temperature in the bathroom. We just run a small electric fan heater.

Why should I forget about it? That’s not my opinion; it’s stated in the DIN standard. The fact is that bathrooms require a higher design temperature than other rooms.
In my case, 45°C (113°F) arrives, and if I don’t want a towel radiator, I set the towel thermostat to zero. Otherwise, I set it, for example, to 3.

Dogma schrieb:

- I think you misunderstood something there: the controlled ventilation system is not designed for heating. The coils only ensure that the incoming air isn’t too cold, nothing more. Whether there is something more energy-efficient, I don’t know, but I didn’t want electric heating elements in the controlled ventilation system because I already had water heating there.
- The towel dryer does have its own circuit (e.g., with a heat exchanger), but the manifold has a magnet to prevent metal shavings from entering the underfloor heating.
- About the supply temperature, you misunderstood again: I said the gas boiler produces 45°C (113°F), not that the underfloor heating runs at 45°C. Please read carefully again.

- You warm up the cold air using a water-based heating coil—do you know what that is? In a standard controlled ventilation system, you only need a preheating coil to prevent freezing. Its energy consumption is negligible compared to the investment cost of water-based pre- and post-heating coils. Anything beyond that is a form of heating.

- If your boiler produces 45°C (113°F), then it produces 45°C. Maybe I didn’t express it clearly. Where exactly do you have the 45°C? Probably in a buffer tank? Whether you later mix that down to 35°C (95°F) is secondary. You generate 45°C that is not strictly necessary. But with a gas boiler, that’s not too critical. Still, it could be more efficient because

- all the extra installation stuff—like water-based heated towel rails and additional water pre- or post-heating coils, mixers, manifolds, etc.—is simply unnecessary if planned correctly. It only adds installation costs and potential points of failure.

As @Bookstar wrote, it’s better to use a fan heater instead. After just 2 minutes of showering, the temperature has already risen by 2°C (4°F). You can also just turn on a hairdryer briefly.

Bookstar schrieb:

You can forget about that with a heat pump. A 3-degree temperature difference is not possible. Anyone who wants that definitely needs an electric auxiliary heater. But I also don’t understand why someone would need such a high temperature continuously in the bathroom. We just run a small electric fan heater.

Why should that not be possible? You simply need the appropriate design and the correct supply temperature to reach around 24°C (75°F), and then adjust the flow rate to the other rooms depending on the desired temperature.
Whether that is more energy-efficient than using a fan heater or hairdryer is another question.

Musketier schrieb:

Why should that not be feasible? You just need the proper system design and the correct supply temperature to reach around 24°C (75°F), and for the other rooms, you reduce the flow rate depending on the desired temperature. Whether this is more energy efficient than using a fan heater/hairdryer, etc., is another question.

Theoretically, it is possible, I agree with you. In practice, this temperature difference is a nightmare.

I define disaster differently somehow.
I don’t quite reach 24°C (75°F), but I do want it to be between 22 and 23°C (72 and 73°F) when showering and using the bathroom.
Even if I raised the heating curve by 2°C (3.6°F) to reach 24°C (75°F), it wouldn’t be a big deal.

Before, we lived in an apartment in a large multi-family building owned by the family. What we used to burn through the heating system with the 60cm (24 inch) thick natural stone walls combined with partial vacancy and heating oil was energetically insane.
The current heating costs are just peanuts compared to that.