ᐅ Ground Source Heat Pump: Bathroom on the Top Floor Too Cold – Is the Heat Distribution Incorrect?
Created on: 27 Dec 2025 15:47
D
dassmooHello,
I am a bit puzzled. Our attic bathroom feels too cold for my wife, and—assuming the cheap thermostat is accurate—the temperature is only about 19°C (66°F). What can I do?
About our heat pump:
We have a ground-source heat pump from Viessmann, with the heating circuit set to 21°C (70°F) from 6 a.m. to 10 p.m. The heat pump is located in the basement. Above that are the ground floor, then the first floor, and finally the attic (so the water has to be pumped up three levels). Whether the heating curve is set to a slope of 0.4 and a base value of 0.0, or a slope of 0.4 and a base of -1.0, the attic bathroom always stays cooler. When the plumbing company was here recently, they checked and found that two of the valves in the heating distributor manifold were not opening properly, and they replaced them (these valves served other circuits on the same attic floor). After that, they used a thermal imaging camera and noted that it was 21°C (70°F). That day, however, the sun was shining. Usually, the thermometer shows a lower temperature.
I just checked the flow rate for the heating circuit at the distributor manifold. It is about 2.4. If I turn it clockwise, the flow decreases (which I don’t want). If I turn it counterclockwise, it reaches a stop at 2.4. It cannot be increased any further in that direction.
The wall thermostat in the bathroom is set to “6” (scale from 1 to 6). What else can I do? I would appreciate any help.
I am a bit puzzled. Our attic bathroom feels too cold for my wife, and—assuming the cheap thermostat is accurate—the temperature is only about 19°C (66°F). What can I do?
About our heat pump:
We have a ground-source heat pump from Viessmann, with the heating circuit set to 21°C (70°F) from 6 a.m. to 10 p.m. The heat pump is located in the basement. Above that are the ground floor, then the first floor, and finally the attic (so the water has to be pumped up three levels). Whether the heating curve is set to a slope of 0.4 and a base value of 0.0, or a slope of 0.4 and a base of -1.0, the attic bathroom always stays cooler. When the plumbing company was here recently, they checked and found that two of the valves in the heating distributor manifold were not opening properly, and they replaced them (these valves served other circuits on the same attic floor). After that, they used a thermal imaging camera and noted that it was 21°C (70°F). That day, however, the sun was shining. Usually, the thermometer shows a lower temperature.
I just checked the flow rate for the heating circuit at the distributor manifold. It is about 2.4. If I turn it clockwise, the flow decreases (which I don’t want). If I turn it counterclockwise, it reaches a stop at 2.4. It cannot be increased any further in that direction.
The wall thermostat in the bathroom is set to “6” (scale from 1 to 6). What else can I do? I would appreciate any help.
R
RotorMotor27 Dec 2025 16:31What did you adjust? The sight glass or the valve?
If you have checked that both are fully open, the only option is to restrict the other (too warm) rooms.
This will increase the flow in the bathroom.
However, this is a very common issue.
The heating surface in the bathroom is usually smaller due to bathtubs, showers, and similar fixtures.
Additionally, pipes are often installed tightly, which makes them longer and reduces the flow.
If you have checked that both are fully open, the only option is to restrict the other (too warm) rooms.
This will increase the flow in the bathroom.
However, this is a very common issue.
The heating surface in the bathroom is usually smaller due to bathtubs, showers, and similar fixtures.
Additionally, pipes are often installed tightly, which makes them longer and reduces the flow.
N
nordanney27 Dec 2025 18:08Why is the heat pump not allowed to run 24/7?
nordanney schrieb:
Why isn’t it allowed for the heat pump to run 24/7?It is allowed, but I simply haven’t had enough time to fully figure it out yet. For sleep hygiene reasons, it would of course be better if the rooms were a bit cooler at night, but due to the thermal inertia, the temperature won’t drop sharply even with night setback.N
nordanney27 Dec 2025 18:42dassmoo schrieb:
For sleep hygiene reasons, it would of course be better if the rooms were a bit cooler at night, but due to inertia, the temperature probably won’t drop suddenly with nighttime setback.Exactly. And at the same time, in the possibly already slightly cooler attic floor, the desired temperature in the bathroom is not reached. Just try running it continuously. Maybe it will improve a bit.By the way, is the color of the heating water intentional? It looks stale – with our last brine heat pump, it was clear.