Why Old Radiator Habits Can Waste More Heat in Winter

During cold months, many homes depend on radiators to keep warm. But longstanding habits in how these systems are used frequently waste energy and result in higher utility bills. Researchers from Europe and beyond have studied how simple behavioral habits - like overheating rooms, blocking radiators or failing to maintain building equipment - can seriously dent efficiency. The findings are not region specific; they apply broadly to households in the United States, Europe and elsewhere in cold climates.

The Overheating and Poor Usage That Cost Millions

Many people mistakenly believe that leaving radiators on full power will provide better comfort. But a study by Jarek Kurnitski of Helsinki University of Technology shows the reverse. His efforts offer startling facts that heating between 20oC and anything further will lead to the decreased performance of the system and increased costs. In fact, each extra degree can increase heating costs by about 10 percent. What happens here is that heating systems begin to under-perform when given a large delta t to operate in, often resulting in excessive revolving cycling and energy being wasted.


The problem is exacerbated in residences where all rooms are heated uniformly, despite the amount of time they’re used. Even unoccupied spaces draw energy, stressing the system unnecessarily. This outdated approach comes from a time when energy efficiency had little importance, yet modern studies clearly show it causes preventable waste.

Radiators Blocked and Out of Touch with the Heating System

Another common practice is covering radiators with furniture or drapes. Though this may seem harmless, research in the REHVA Journal shows that these types of blockages can decrease heat output by 20 to 30 percent. Critically these results are derived from tests of panel radiators in laboratories across Europe, where airflow disruption mechanism made a substantial impact on the performance.

Radiators work by both convection and radiation. When air flow is impeded, warm air doesn’t move around well so a good deal of heat simply gets stuck behind things. This causes the HVAC system to work harder to keep the desired temperature, resulting in increased energy consumption.

The Impact of Neglected Maintenance

Neglecting routine maintenance can impact the radiator’s efficiency. In an research published in 2014, titled “Low Temperature Radiator Heating Distribution and Emission Losses,” Marika Maivel at Tallinn University of Technology found that bleeding can save up to additional 5 percent heat loss when radiators are not bled. This creates air pockets that block proper circulation of water, creating cold spots and less performance.

This becomes even more problematic in older buildings where systems are already likely less efficient. Bleeding the radiators on a regular basis releases that trapped air, ensuring correct heat distribution and improving overall efficiency with very little effort.

Drafts and Structural Heat Loss

External factors can also hinder radiator effectiveness even when they are working normally. According to research, 20 to 25 percent of indoor heat can leak out through gaps around windows and doors. This results in constant heat loss, making radiators work harder to keep indoor temperatures stable.

The research of Jesse Chirakijja at Imperial College London links suboptimal heating behaviors to bigger energy and health issues. His research indicates that homes with energy-inefficient heating, especially in low-income neighborhoods, experience greater energy demands and increased health risks in winter. Drafts compound these problems by developing a continuous airflow that sent warm air out the home and cold air into it.

Older systems are inefficient because of the physics behind it.

Older radiator systems, particularly the cast-iron ones common in pre-1940 homes, are especially affected by these habits. They have a higher water content and therefore require more time to get up to temperature, which magnifies the impact of inefficiencies. When air was blocked or trapped inside, these systems lost heat faster and required more energy to recover.

The physics is straightforward. Air pockets are insulators within the radiator, and so slow heat transfer. Blocked airflow inhibits convection and overheating increases the system cycled, causing energy losses of up to 10 to 15 percent. Combined, these factors compound inefficiency and increase heating costs.

Real-World Savings Through Simple Changes

The good news is that most of these inefficiencies are preventable. For decades, studies all over Europe and energy audits in the United States have shown that even before you touch a radiator or a thermostat (or replace them), behavioral changes alone can be expected to reduce heating bills by 10 percent to 30 percent. Annual radiator bleeding could recover 5 percent of the loss witnessed in the Tallinn study, whilst not obstructing radiators with furniture etc can recover 30 percent of heat output lost.

Another important measure is sealing drafts, which can reduce heat loss by as much as a quarter. 17 No central heating, proper modern controls such as thermostatic radiator valves enable households to heat only the parts of the home they use, avoiding unnecessary energy wastage.

A World View on Energy Efficiency

Much of the research is emanating from institutions in Europe, including Tallinn University of Technology (in Estonia), Helsinki University of Technology and Imperial College London, but the principles are universal. Houses in the United States, especially in colder climates with steam or hot-water systems, have similar issues. The physics of heat transfer works the same everywhere, making these results globally relevant.

Overall, the evidence is clear. Old radiator practices can waste tons of energy in the home. By following simple, evidence-based practices that can help with comfort and cost and make their heating systems dramatically more efficient — without spending money on new equipment.