Weather compensation can make a heat-pump controller look more technical than it really is.
The core idea is simple:
colder outside → warmer heating water
milder outside → cooler heating water
The control changes the heating-water target as outdoor conditions change.
Why this exists
A building usually loses heat faster in colder weather.
If the heat pump supplied unnecessarily hot water during mild conditions, it could be working harder than required. Weather compensation is intended to match the water temperature more closely to the heating need.
This is about the temperature of the heating water, not the room target.
Why there is no universal perfect curve
Two homes can need different water temperatures at the same outdoor temperature.
Differences can include:
- heat loss;
- radiator or emitter size;
- underfloor-heating design;
- building construction;
- occupancy;
- control strategy;
- the way the system was commissioned.
That is why a heating-curve number from a forum, video, or another owner’s controller is not automatically useful for your installation.
The better question is whether your home is comfortable under different outdoor conditions.
Read the comfort pattern
Patterns are more useful than isolated numbers.
Too cold in both mild and cold weather
Do not immediately assume the curve is the only cause.
Check the room target, schedule, operating mode, hot-water operation, and whether the system is behaving normally.
Comfortable in mild weather but too cold when it becomes much colder
The colder-weather part of the control strategy may be worth investigating.
That still does not prove a specific curve change is the answer. It tells you where the pattern appears.
Too warm in mild weather but comfortable in colder weather
The mild-weather side may be delivering more heat than the home needs.
Only one room is cold
Do not begin with a whole-system weather-compensation change.
A local room or zone problem should be investigated locally first.
Slope, shift, offset, or two points
Manufacturers represent heating curves differently.
Your controller may use:
- two temperature points;
- a slope;
- an offset or shift;
- a simplified numerical scale.
The labels are system-specific.
Conceptually, the slope changes how strongly the target water temperature responds as outdoor temperature changes. A shift or offset moves the target more broadly up or down.
Use the exact user documentation for your controller before interpreting a setting.
Before changing anything
Weather compensation is an Amber area on many systems because the control may be user-accessible but its effect depends on the installation.
Before changing it:
- find the exact manufacturer user documentation;
- photograph or record the current setting;
- confirm the control is intended for owner use;
- write down the comfort problem you are trying to solve;
- change one thing only;
- allow the building enough time to respond.
Do not change the heating curve, room target, overnight setback, and hot-water schedule together. If the result improves or worsens, you need to know which change caused it.
A worked pattern
Imagine the main living room is close to its 20°C target during colder weather around 2°C outside, but repeatedly reaches roughly 21.5–22°C in milder weather around 9–11°C.
That pattern suggests the colder-weather end is broadly adequate while the milder-weather side may be delivering too much heat.
If the exact controller documentation confirms that the relevant mild-weather control is owner-adjustable, a small documented change can be tested while leaving the cold-weather point, room target, setback, and hot-water schedule alone.
The important lesson is not a specific number. It is the decision process.
When to stop adjusting
Stop and seek installer or competent professional input when:
- sensible owner settings still cannot maintain reasonable comfort;
- the next step appears to require a protected installer menu;
- faults appear;
- you no longer know the original configuration;
- the comfort pattern does not match the explanation you are testing.
A poorly performing installation cannot always be corrected from the household controller.
For electricity concerns, use the high electricity-use checks. For escalation, use when to call the installer.
Important: This guide explains the decision process, not a universal heat-curve setting. Follow the instructions for your exact heat pump and controller.