Is Night Setback Worth It? When It Actually Pays Off in Existing Buildings

Night setback is worth it mainly in uninsulated older buildings with sluggish radiators, where it saves a real 5 to 12 percent of heating energy. In well-insulated buildings and with underfloor heating, but above all with heat pumps, the morning reheating wipes out nearly all of that saving for housing companies running a full portfolio.

For asset and operations managers, the answer therefore comes down to the individual building: what matters is how quickly a building cools down and how fast the heating brings it back up to temperature afterwards. That ratio between cooling speed and reheating time decides whether a setback ultimately saves energy or just puts more strain on the boiler each morning.

Anyone rolling out setback schedules across a portfolio runs into four variables that decide between real savings and extra cost:

Night Setback in Older Buildings: When Does the Temperature Drop Actually Pay Off?

In unrenovated older buildings with radiators, night setback is usually the most effective operational lever that costs nothing to implement: the German consumer advice centre puts the saving against continuous operation at 5 to 12 percent of heating energy, with some sources citing up to 15 percent for a very large temperature drop.

The reason lies in how two properties interact: a thin, poorly insulated building envelope cools down noticeably overnight, but radiators with a small water volume respond almost instantly once the heating comes back on in the morning. Reheating stays quick, so a genuine net saving is left over from the energy saved overnight.

Good to know: The decisive factor is called thermal mass, meaning how long a building takes to settle back into equilibrium after a temperature change. Solid, well-insulated buildings respond sluggishly and barely cool down, while light, poorly insulated buildings react quickly in both directions. This figure tells you far more about the benefit of a setback than a building's construction year alone.

The larger the temperature drop, say from 21 down to 16 degrees Celsius, the bigger the calculated saving. How far that can be pushed in a specific building without risking comfort or moisture problems depends on that building's own cooling limit.

Why Do Well-Insulated Buildings and Underfloor Heating Barely Benefit?

In well-insulated buildings with high thermal mass, night setback achieves almost nothing, because the indoor temperature barely drops overnight anyway. In new-builds with modern insulation, the effect usually stays below 3 percent, and with very good insulation and high building mass it drops to practically zero.

With underfloor heating, a second effect comes into play: the screed stores heat and releases it slowly, so reheating often takes several hours. In these systems, a constant, moderately low target temperature delivers the same comfort at lower energy cost than a nightly temperature drop whose reheating phase eats up half the morning.

For housing companies with a mixed portfolio, that means a blanket setback programme applied across all properties overlooks exactly this difference, and in modern buildings it can end up costing more energy than it saves if the heating curve pushes too aggressively during reheating.

Why Is Night Setback Usually Counterproductive for Heat Pumps?

With heat pumps, the effect often flips: reheating in the morning demands a noticeably higher flow temperature, and a larger gap between heat source and flow temperature noticeably worsens the system's seasonal performance factor (SPF) and COP. The harder a heat pump has to work against cooled-down building components in the morning, the more electricity it needs for the same amount of heat.

It gets particularly unfavourable with air-to-water heat pumps: reheating often falls right into the coldest morning hours, exactly when the heat source itself is at its least efficient. The extra electricity needed for reheating can outweigh the heat saved overnight, so the night setback ends up costing more energy overall than it saves.

Recommended approach: ELCO recommends limiting the temperature drop for heat pumps to a maximum of 1 to 2 degrees and skipping a classic night programme with a full setback altogether. In practice, a constantly low flow temperature runs more economically.

For portfolios running heat pumps, it pays to check the data situation before operation even starts: our article on which load profiles and temperature data are typically missing before a heat pump project in a multi-family building looks at exactly that gap. Shifting operation to cheaper electricity hours through dynamic price-based control is usually a more economically sound lever for heat pumps than a temperature drop in the first place.

What Savings Are Realistic Across a Property Portfolio?

Across a portfolio, realistic ranges vary considerably depending on which system is installed in each property. The table below places the figures from this article in context; the actual saving always depends on the individual building:

Hydraulic balancing illustrates that night setback is only one of several operational levers available in existing buildings. Our article on heating optimisation levers, costs and savings potential in existing buildings looks at how these levers combine in day-to-day operation.

What Risks Come with Excessive Cooling and Mould?

If the setback is set too aggressively, two problems can hit at once: a room temperature that drops below the legal minimum for rented housing, and a measurable rise in mould risk from a building-physics standpoint. Under established German case law, the temperature must not fall below roughly 16 to 18 degrees Celsius at night, and during the day, usually between 6am and midnight, central heating has to reach 20 to 22 degrees regardless.

The Cologne Local Court (Amtsgericht Köln) ruled that a night setback leaving rooms at just 16 to 17 degrees by morning already constituted a defect of the rented property, entitling tenants to a rent reduction. For housing companies managing large numbers of properties, that translates into a real cost item whenever setback times are set too aggressively.

Building-physics calculation: If room temperature drops from 20 degrees at 60 percent relative humidity to 15 degrees while the actual moisture content stays the same, a building-physics calculation from a surveying firm shows relative humidity climbing to around 80 percent, a level already sufficient for most types of mould.

Continuous monitoring of flow and return temperatures across a portfolio makes critical deviations like this visible long before tenants report a defect or mould becomes visible. The annual statement usually only flags the problem months too late. Our article on heating monitoring in multi-family buildings, covering data, alerts and the practical benefit shows what that looks like in day-to-day operation.

Why Are Fixed Time Switches Too Blunt for Multi-Family Buildings?

A centrally programmed night setback is often difficult to enforce legally in rented multi-family buildings in the first place, because individual flats, for shift workers for example, need to stay heatable at any time. In practice, that usually leaves only a very moderate central setback, or individual control through the thermostat in each flat.

That considerably weakens the effect of a central time programme compared with a genuinely coordinated setback. On top of that, a single schedule can't reflect either the differing insulation or the differing usage patterns across the properties in a portfolio. A setback time that makes sense in one building can leave flats cold in the next, or trigger unnecessary reheating.

How Does a Digital Building Twin Control Setback on Demand?

Instead of a blanket schedule, a digital building twin like KUGU EOS (Energie-Optimierungssystem, KUGU's energy optimisation system) continuously recalculates the optimal flow temperature, based on each building's individual thermal inertia and current weather forecasts, complemented by sensor and usage data from live operation. This function, known at KUGU as EOS Temperaturführung (temperature control), adjusts heating phases individually to the real demand of each property, independent of a single uniform time window applied across the whole portfolio.

In a pilot project with the municipal housing company Gewobag, KUGU achieved the contractually guaranteed 12 percent saving in every single one of ten existing buildings, in some cases considerably more. Between October and March, that added up to roughly 260,000 kWh of energy and more than €18,000 in energy costs saved, alongside over 50 tonnes of CO₂ avoided.

Good to know: In another KUGU project in two older buildings in Leipzig, savings of 39 and 33 percent respectively were measured within just two months. That figure comes from the transitional period heading into spring and is a seasonal outlier, well above what you'd expect as an annual average. For ongoing operation, the benchmark figures remain the contractually guaranteed 12 percent and the more than 20 percent average saving delivered by the KUGU Energy Suite.

There's a further economic point in housing companies' favour here: the running costs of predictive, data-based control with remote monitoring are recoverable under Section 7(2) of the German Heating Costs Ordinance (Heizkostenverordnung), so no lasting extra burden falls on the owner side. Our article on digital heating optimisation and how a digital twin drives efficiency describes in detail how a digital twin is technically built and which data it needs.

From Case-by-Case Checks to Digital Standard Operation

The real conflict of objectives in existing portfolios usually only becomes visible once you're in day-to-day operation: a time programme that still works in an older building with radiators turns into a risk the moment it's applied unchanged to insulated buildings, underfloor heating and heat pumps within the same portfolio. And wherever a central setback is even legally permissible, the ability to calibrate it individually for every building is usually missing.

A digital building twin resolves exactly this conflict, because it continuously derives its own thresholds for every property from thermal inertia, weather and usage. That makes the question of night setback across a portfolio largely redundant, because the software answers it building by building, on an ongoing basis.

As a next step, it's worth taking quick stock of your portfolio by building type and heating system: which properties are unrenovated older buildings with radiators, where does a classic setback still pay off at all, and where should demand-based digital control replace rigid time switching before comfort complaints or moisture damage make the decision for you.

How Far Can a Rented Flat's Temperature Drop at Night?

Not below roughly 16 to 18 degrees Celsius, or established German case law treats it as a defect of the rented property. In 2016, the Cologne Local Court ruled that a night setback leaving rooms at just 16 to 17 degrees by morning justified a rent reduction. During the day, usually between 6am and midnight, central heating has to reach 20 to 22 degrees regardless.

Why Is a 1 to 2 Degree Drop Already Enough for Heat Pumps?

Because every additional degree of temperature drop demands a higher flow temperature during reheating, which noticeably lowers the heat pump's seasonal performance factor and COP. Manufacturers therefore recommend limiting the drop to 1 to 2 degrees. A classic night programme with a full temperature drop tends to push costs up rather than down for heat pumps.

Can Property Management Switch Off the Heating Centrally at Night?

No, switching the heating off completely overnight is legally risky in rented multi-family buildings, because individual flats, for shift workers for example, need to stay heatable at any time. In practice, that usually leaves only a moderate central setback or individual control per flat. That noticeably limits the effect of a central time switch compared with individual heating control.

How Quickly Does Night Setback Raise the Risk of Mould?

Even a drop from 20 to 15 degrees Celsius can push relative humidity from around 60 up to roughly 80 percent, with the actual moisture content unchanged, a level already sufficient for many types of mould. Poorly insulated exterior walls and room corners with little air circulation are most at risk. Adequate ventilation and a lower limit of around 16 degrees reduce that risk considerably.

Does a Demand-Based System Like KUGU EOS Pay Off Compared with a Simple Timer?

Yes, because the running costs of predictive, data-based heating control are recoverable under Section 7(2) of the Heizkostenverordnung, so no lasting extra burden falls on the owner. The system also continuously adapts to weather and usage without needing manual readjustment, which makes it more economical than a rigid time programme over the course of a heating season.