Decarbonizing Existing Buildings Without Waiting for the Next Renovation

Decarbonizing existing buildings doesn't have to wait for the next facade renovation or heating system replacement. Hydraulic balancing, continuous monitoring and better temperature control cut heating energy consumption by a proven 10 to 20 percent, often within a few weeks, with no scaffolding and no funding application required.

For housing companies, a lot rides on this. The renovation rate fell to a record low in 2025, while CO₂ costs and inspection obligations keep running regardless of renovation progress. If you wait for the next major renovation cycle, you give up exactly the savings that are already sitting in day-to-day operations today.

Where Can You Find the Fastest CO₂ Savings in Existing Buildings?

The fastest savings sit in the day-to-day operation of your existing heating system. Hydraulic balancing cuts heating energy consumption by up to 15 percent, and continuous monitoring of the system adds another 10 to 20 percent in cost reductions according to trade publications, all without any construction work.

The BaltBest research project run by EBZ Business School tracked this exact effect over three years, using 7,000 sensors and around 4 billion data points across 1,200 households. The result: better operational management and adjusted system settings alone save 10 to 20 percent of energy per property, purely through how the system runs. A BMWi/BMWE study based on DIN EN 15232 backs this up with a concrete factor: moving from an average building automation level (Class C) to a higher level works out to roughly 19 percent in savings. That gives you a way to evaluate control technology like any other investment, with a clear, measurable before-and-after figure.

Hydraulic balancing, explained briefly: hydraulic balancing sets the water flow to each radiator so every room gets an even, actually-needed amount of heat. Without this adjustment, pumps and boilers typically run at higher temperatures and flow rates than necessary, just to keep the furthest radiators supplied.

This lever stays effective mainly because so few buildings use it: more than 80 percent of heating systems in German residential buildings still haven't been balanced. For housing companies with larger portfolios, that means savings potential sitting dormant in almost every existing building, and most of it can be unlocked with a single technician visit.

Trade publication Gebäude-Energieberater confirms this range across several field reports: continuous monitoring of the heating system lowers operating costs by another 10 to 20 percent, regardless of whether hydraulic balancing has also been carried out. The two measures complement each other, since balancing corrects heat distribution while monitoring keeps watching, year after year, whether that correction holds.

What Does Digital Monitoring Reveal About the Real Condition of a Heating System?

Digital monitoring often shows within days how far a system runs from its optimum, largely regardless of the building's construction year. At Städtische Wohnungsgesellschaft Waiblingen, analyzing operating data alone identified around 20 percent in savings potential, across a portfolio spanning older and newer buildings built between 1991 and 2020.

An even more revealing case comes from a pilot project run by Beamten-Wohnungs-Baugenossenschaft Düsseldorf across around 3,000 residential units, documented by dena as a good-practice example. Digital remote monitoring of a gas heating system uncovered specific misconfigurations, including a poorly placed outdoor temperature sensor, that no one had previously noticed and that kept the system running too warm for years. Errors like this often go undetected for years in a conventionally maintained boiler room, because they don't trigger any fault alert and just quietly waste energy in the background. Conventional maintenance drops in at set intervals to check that everything's fine. Ongoing digital heating optimization in operation evaluates the data continuously and flags deviations before they turn into chronic excess consumption.

Case in point, Düsseldorf: a single misplaced outdoor temperature sensor was enough to shift the heating curve of an entire system permanently. Only digital remote monitoring brought the error to light, one that conventional maintenance without continuous data analysis would never have caught.

For housing companies with a mixed portfolio, that's the real strength of monitoring: it catches concrete, building-specific errors, like misplaced sensors or wrongly set heating curves, that often get fixed with a single parameter change.

How Does Operational Optimization Affect CO₂ Cost Allocation?

Operational optimization affects a housing company's cost position directly through the CO₂ Cost Allocation Act, on top of pure energy consumption. The act ties the landlord's share of CO₂ costs directly to a building's specific CO₂ emissions: for particularly emission-intensive properties at 52 kg CO₂ per square meter and year or above, landlords cover 95 percent of the CO₂ costs, while for highly efficient buildings under 12 kg CO₂ per square meter and year, that share drops to 0 percent.

This ten-tier model has applied in full since January 1, 2025, at a certificate price of 60 euros per ton in the national system for 2026 (73.86 euros once the EU ETS 1 share is factored in). If you lower your building's specific CO₂ emissions through better controls, temperature management and load management, you can move into a cheaper tier of the model and genuinely cut your own cost share, without changing the energy source itself. Few measures let you read the economic effect this directly out of the legal text.

Platform-based solutions for AI-supported energy optimization in existing buildings target exactly this link: the KUGU Energie-Optimierungssystem (EOS) uses a digital building twin to continuously adjust the heating curve, supply temperature and operating times based on weather data, usage patterns and system behavior. In practice, systems like this average more than 20 percent in savings potential, with a guaranteed minimum of 12 percent, and that feeds straight through to your CO₂ cost tier: your landlord share drops accordingly.

Which Levers Scale Across a Portfolio Immediately, and Which Stay Building-Specific?

Every measure built around data and controls, leaving the building's physical structure untouched, scales across a portfolio. Hydraulic balancing, digital monitoring and automated temperature control roll out across hundreds of properties following the same pattern, because they work through system controls, independent of each building's individual construction.

Measures that depend on the building's structural starting point stay building-specific: swapping in a heat pump at a property with high supply-temperature needs, or insulating a particular facade, for example. District heating conversion belongs in this category too, provided a network is even available at the site. The heat pump share in the German building stock has nearly doubled since 2019, yet still stood at just 4.3 percent of all existing buildings in 2024, a huge potential that has to be unlocked building by building and needs a much longer planning runway than a portfolio-wide rollout. For prioritization, that means pulling the scalable, data-driven levers first, then capturing savings across the entire portfolio before the first facade gets touched.

Load management deserves an honest look at the data situation: solid, portfolio-wide figures on load management and sector coupling in multi-family buildings remain scarce, and most available figures come from single-family homes, which don't transfer directly to large portfolios. If you want to pursue this lever, test it building by building first, for instance by tying heat pump operating times to dynamic electricity prices, before locking it into your portfolio-wide priorities.

Why Does the Myth That Decarbonization Needs a Big Investment First Cost the Industry Real Money?

This misconception costs twice over: you delay the cheapest measures and put the budget into the most expensive ones. According to Dr. Ingrid Vogler (GdW) and Dr. Hans-Joachim Riechers (VDPM), it's a common misconception in the housing industry that every energy-saving measure pays for itself automatically through the energy costs it saves. At shallower renovation levels, avoidance costs quickly climb to 10 to 14 euros per kilowatt-hour saved, while operational measures in day-to-day running usually sit well below that. The 4-to-14-euro range per kWh is based on pre-2022 pricing, so the absolute figures have likely risen since, though that changes little about the scale of the gap between operations and a full renovation.

Good to know: avoidance costs describe how much money a measure costs per kilowatt-hour saved. For deep renovation levels like a full retrofit, GdW/VDPM puts this at 10 to 14 euros per kWh; for purely operational measures, the figure comes out far lower, since no building fabric needs to change.

How deeply this misconception sits in practice shows up in an industry survey by aedifion and Rueckerconsult among developers, portfolio holders and financiers: more than 50 percent of the companies surveyed have no decarbonization concept for their portfolio, a quarter don't even know their own CO₂ output, and 60 percent lack a fixed budget for getting there. If you don't know where your portfolio stands, you can't decide which lever pays off first, and you end up pushing that decision further down the road without ever meaning to.

The economic cost of waiting also shows up in property value itself: energetically poor, unrenovated buildings now carry a value discount of up to 40 percent compared to renovated equivalents, according to industry figures. Operational optimization won't change that valuation overnight. It buys you time and documented progress while the actual renovation roadmap still gets built.

What Does the Shift From the GEG to the Building Modernization Act Change About the Urgency?

The shift from the Buildings Energy Act (GEG) to the new Building Modernization Act (GModG) mainly changes the shape of the regulatory pressure behind operational optimization, not whether it exists. Under the GModG, the blanket 65 percent renewable energy requirement for new heating systems falls away in 2026, and owners once again decide independently what type of heating to install.

What stays exactly the same are the inspection and optimization obligations for older, water-based heating systems under §60b and §60c: housing companies with buildings of six or more residential units must have their systems inspected and optimized on a staggered schedule, depending on installation date, by September 30, 2027 at the latest. These deadlines run regardless of whether a renovation is planned, and that's exactly where operational optimization helps: hydraulic balancing, cleaned-up temperature control and working monitoring already meet these requirements in many cases, with no additional investment required.

Deadlines at a glance: for heating systems installed before October 1, 2009, the deadline for inspection and optimization under §60b/§60c GEG runs out by September 30, 2027 at the latest. For buildings with at least six residential units, this obligation continues to apply regardless of the GModG taking effect.

Reading the GModG as an all-clear is a mistake. What still matters is the documented condition your system is actually running in. A data-based perspective on decarbonization delivers exactly the evidence that inspection obligations, ESG reporting and cost control all demand alike.

The Biggest Lever Sits in the Boiler Room, Long Before Construction Starts

The real takeaway from the climate report, the CO₂ cost allocation model and the renovation statistics is a shift in sequence: you can read from your system's documented operating condition how urgent and how expensive the next step will be, before any renovation roadmap even exists. The building sector exceeded its legal carbon budget again in 2024, by 4.7 million tons of CO₂ equivalents, while the renovation rate fell to 0.67 percent. You close that gap fastest by making visible what's actually happening in the basements of your existing buildings right now.

For your portfolio, that means something concrete: start with an inventory of your own systems, prioritize hydraulic balancing and monitoring, and make the CO₂ cost impact visible building by building. That gives you a data foundation later on to justify renovation decisions economically too. Start with an honest question: which buildings in your portfolio use more energy than their construction explains, and where does the cause sit in how the system is controlled?

An inventory like this doesn't add another year of planning time, and it doesn't require a funding application. Within a few weeks, it gives technical, ESG and finance teams solid figures on consumption, costs and CO₂ tier for each building, numbers that make later renovation decisions economically sound in the first place.

Frequently Asked Questions About Decarbonizing Existing Buildings

How Quickly Do Savings Show Up After Hydraulic Balancing?

Most housing companies see the effect clearly in consumption data within the very first heating season after balancing. Because the measure acts directly on heat distribution and needs no construction phase, the usual delay between investment and measurable impact falls away.

Is Operational Optimization Enough to Move Into a Cheaper CO₂ Cost Tier?

Yes, provided the optimization genuinely lowers the specific CO₂ output per square meter, it can move a building into a lower tier of the CO₂ Cost Allocation Act's ten-tier model. How large the effect turns out to be depends on how close the building already sits to the next tier boundary.

From What Number of Units Do the §60b/§60c GEG Inspection and Optimization Obligations Apply?

Six residential units is the threshold, and even then, only for older, water-based heating systems. The exact deadline depends on the system's installation date and runs on a staggered schedule through September 30, 2027 at the latest.

Does Operational Optimization Lose Importance When the GModG Replaces the GEG in 2026?

No, the inspection and optimization obligations for existing systems stay fully in place when the GModG replaces the GEG. Only the renewable energy requirement for new heating systems has changed; the requirements for the ongoing operation of existing systems continue to apply exactly as before.

Does Digital Monitoring Pay Off for Smaller Portfolios Under Six Units Too?

Smaller properties benefit from monitoring too, though with a different priority than large portfolios. Larger portfolios pay it off faster through scale across many buildings, while for smaller properties, monitoring pays off mainly where consumption is already noticeably high or fault alerts keep coming up.