Towel radiator for air-water heat pump

Underfloor heating without towel radiator

- Is this sufficient to maintain a 10m² bathroom with shower & bathtub at 21°?
- Does the bathroom remain cooler than the other rooms due to the smaller heating surface?

According to DIN 12831, the standard temperature in the bathroom is 4° higher than in living rooms. Does this mean that underfloor heating must be designed to reach at least 24°? If this does not work, your general contractor/heating installer may have a problem. So, in their own interest, they will try everything. Subtly let them know that this is important to you.

In my opinion, the bathroom temperature should be at least 23° in any case. With a baby (bathing, diaper changing), then at least 25°. If this all has to be achieved despite the area or efficiency of the heating system, then installing a fan heater or infra-red heater can also be worthwhile. The latter are available not only as mirrors but also in unobtrusive picture form.

1.) Underfloor heating without towel radiator

- is this enough to keep a 10m² bathroom with shower & bathtub at 21°?
- does the bathroom stay colder than the other rooms due to smaller heating surface?

This cannot be answered without room-specific heating load calculation. Opinions and estimates are misplaced!

For us, it is sufficient with close occupancy including occupancy of the shower and with an adjacent cooler bedroom. We do not get significantly above 21° unless we increase the heating curve only because of the bathroom and throttle all other rooms. We planned for only 21° + electric heating and thus waived heating surfaces in the walls.

Typically, however, it is not enough, see other threads here about optimizing heat pumps. The heating surface is limited in the bathroom and the heat demand is higher.

2.) Underfloor heating with towel radiator on the same heating circuit as the bathroom

- the heating surface is somewhat increased but the towel radiator only has a temperature of 21°
- does the advantage of the "larger" heating surface outweigh?

The towel radiator has the supply temperature, which is somewhat higher than 21°. This option should be avoided. It hardly brings any benefit, but the radiator introduces rust into the system.

3.) Underfloor heating with towel radiator on a separate heating circuit

- probably the energetically worst solution

Like 2, but it must be strongly throttled or you get thermal short circuits. That means the temperature of the towel radiator would be somewhat lower than in option 2, because in option 2 the towel radiator could be placed at the beginning of the heating circuit and the rest of the circuit absorbs the heat.

4.) Underfloor heating with electric towel radiator

- switchable as needed

Either for briefly increasing heating, or the underfloor heating should also be installed in the walls if it should be somewhat warmer permanently than in the rest of the house. More comfortable than an electric towel heater would be an IR panel.

To state it explicitly once again..

Option 5) Extension of the underfloor heating into wall surfaces
If you do the balancing, all rooms in the house reach the desired temperature, but the bathroom remains at, for example, 19° with the otherwise appropriate flow temperature, then the electric heater alone is not the right solution.

What would underfloor heating in the wall look like?

How would underfloor heating in the wall look like?

Depending on whether it is drywall or brick. For brick, mounting rails are screwed to the wall. The underfloor heating pipe is then clipped onto them. Afterwards, plastering. There are many pictures of this on the internet.