Many industry professionals believe that heat pumps were essentially designed for new buildings with low heat losses, ideally with underfloor heating. There is some truth to this – in such buildings, heat pumps operate very economically. Sometimes heat pumps can also be installed in older buildings, but this requires bringing the building and its installation to an appropriate standard, along with the proper selection of the heat pump itself. Otherwise, it will not be a cost-effective heating solution, and quite the opposite.
However, the market is flooded with salespeople whose primary goal is to sell heat pumps. You might not always get the full picture from them, especially regarding the costs of adapting an older building, as full disclosure could discourage you from making a purchase. Let’s be honest – in some buildings, a heat pump should never be installed, especially not in the state the buildings were in at the time of installation. This is a problematic aspect of the heat pump market, leading to people being shocked by massive electricity bills (which can literally be staggering). Read on to learn about the most common reasons why a heat pump consumes more electricity than expected and what you might be able to do about it.
✅ Thermal insulation, including the insulation of the building facade, is fundamental. In a broader sense, it also involves ensuring the overall protection of the building against heat losses.
Some people, particularly in rural areas, who previously heated their homes with traditional solid fuel boilers, pellet stoves, eco-pea coal, wood, or coal, believe that switching to a heat pump means using a heating source similar to any other. The assumption is that if a boiler was sufficient, then a properly sized heat pump should also be able to heat the house. In traditional high-temperature heating sources, such as boilers, heating a house is relatively easy, and the role of building insulation is often underestimated. Indeed, homes might feel cold in the morning, but once the boiler is turned on, heat returns almost immediately.
We strongly advise against installing a heat pump in a poorly insulated building. If a salesperson offers to install a heat pump in a building without basic insulation, either their competence or integrity should be questioned. This setup will definitively not work efficiently, and the heat pump will compensate with high electricity consumption.
However, it's important to remember that insulation is not just about adding a layer of polystyrene to the building's walls – there are other aspects to consider as well.
Windows are one of the main points of heat loss in buildings. Anyone with a room with large windows knows this well. Modern windows are airtight, significantly reducing heat loss and helping to retain warmth in the building. This allows the heat pump to work less and consume less electricity. If you have old windows with drafts, replacing them with new ones will definitely result in noticeable savings in electricity consumption by the heat pump. Of course, replacing windows is usually a considerable expense, but it is a worthwhile investment.
Interestingly, old, drafty windows did have some advantages. Rooms with such windows were better ventilated, and air exchange is generally healthy. However, it is better to ventilate a room in a controlled manner before bedtime than to lose heat throughout the entire heating season.
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The roof, specifically its insulation, is a significant source of heat loss. Unfortunately, replacing a roof is usually very expensive, but if it’s planned, it’s worth addressing sooner rather than later. Poor insulation or leaks in the roof certainly lead to higher electricity consumption by the heat pump, but they also increase heating costs regardless of the heating method used.
✅ Is an old heating system suitable for use with a heat pump?
It depends on what is meant by an old heating system. If it’s a very outdated system operating in an open circuit, our opinion (shared by many) is that a heat pump should never be installed in such a building. It will always result in high electricity consumption by the heat pump, making it challenging to achieve a return on investment. Exceptions might exist, such as if a comprehensive renovation of the entire system, converting it to a closed circuit, is planned shortly after the heat pump installation, perhaps the following year – but this is likely the only justifiable exception.
In somewhat older systems operating in a closed circuit, there are probably no significant contraindications for working with a heat pump. Basic methods, such as descaling the system, can help ensure its functionality. If the house has underfloor heating, the situation is straightforward – such a system is essentially ideal for use with a heat pump, and there’s no need to worry about excessive electricity consumption.
However, if the system has been operating with radiators, it’s worth taking a closer look at them, which is discussed below.
If the system includes old cast-iron radiators with large water capacity, typically found in old open systems, it will almost certainly require modifications.
If the system is closed (considered by many experts as the only setup guaranteeing the economic operation of heat pumps), you might consider replacing the radiators with low-temperature models. Low-temperature radiators are more economical to operate, as they perform efficiently even at lower supply temperatures. Operating the heat pump at a lower temperature always translates to electricity savings. This is why underfloor heating is often recommended for use with heat pumps – it only requires a supply temperature of around 35°C, whereas radiators typically need higher temperatures to effectively heat a building.
This is a broader issue, and if such problems are suspected, it’s best to call an independent team to conduct an audit. Various issues could arise, ranging from an improperly selected heat exchanger to an insufficient volume of water in the heat pump circuit. Problems could also stem from the home's heating system itself, such as an overly extensive layout requiring additional heating circuit distributors, hydraulic separators (low loss headers), or mixing valves to balance the system and eliminate cold returns.
Over time, certain components of a heat pump may age and wear out. One such component can be the gas-to-water heat exchanger, which acts as a condenser and is often a plate heat exchanger. After years of operation, it may require cleaning to remove deposits, improving the heat pump’s efficiency.
In some heat pump systems, particularly monobloc heat pumps filled with glycol, an additional independent plate heat exchanger is used to separate the glycol from the heating system. Flooding the entire system with glycol is generally not recommended. If such an exchanger operates for years without cleaning, its performance may degrade, reducing heat transfer. Cleaning the heat exchanger in such cases can restore its effectiveness.
It’s also worth noting that the use of a plate heat exchanger to separate the heat pump from the heating system isn’t limited to monobloc models. This method is sometimes employed for split-type heat pumps to protect them when connecting to older, unmodernized installations. Although installing a heat pump in such systems is often discouraged, this configuration is sometimes used, and isolating the pump with a plate heat exchanger can be justified.
✅ Regardless of the configuration, scaling or fouling of the heat exchanger can lead to inefficient heat pump operation and excessive electricity consumption.
Problems can also arise when the heat exchanger is not scaled but is undersized for the heat pump. In such cases, the heat pump cannot transfer sufficient heat from the circuit. Its sensors quickly reach the set temperature, shutting down the device. The heat pump then restarts when the circuit temperature drops.
This frequent cycling prevents the heat pump from operating efficiently, leading to higher electricity consumption and a less effective heating system.
An undersized heat exchanger can result in increased electricity use and an inadequately heated home. While this issue is manageable with a heat pump, using an undersized heat exchanger with more inert heating sources, such as old coal boilers or fireplaces without sensors to regulate heat, can pose a serious risk. In such cases, the rise in temperature and pressure could cause water to boil, potentially damaging the system. Fortunately, heat pumps are equipped with sensors that should shut them off before such problems occur.
Heat exchangers for heat pumps are often undersized, even by professionals. Selecting a heat exchanger for a heat pump is not straightforward, and installers frequently choose exchangers as if they were for traditional heating boilers, which is a clear mistake. Heat pumps are designed to operate economically with low temperature differences, making it mathematically more challenging to transfer the required power in kW. Therefore, heat exchangers for heat pumps require significantly larger surface areas compared to similar devices for more traditional heating systems. A heat pump is not a boiler, and its operating characteristics differ slightly.
Many people do not experiment with the operating temperature of their heat pump at home, and it could be argued that they are unaware of the full potential of their heating system. Often, lowering the operating temperature of the heat pump could provide equally effective home heating without reducing the thermal comfort of the household. Many users set the same temperature on their heat pump throughout the year, regardless of whether there are severe frosts outside or it’s autumn with temperatures around +10°C. This is impractical; it’s worth taking an interest in the system. The pump should operate at the lowest possible temperature that still ensures comfort. If comfort is compromised, the temperature can always be adjusted upwards.
Properly setting the heat pump is not difficult and only requires a willingness to experiment a bit.
This is also why heat pumps are often associated with underfloor heating. Underfloor heating is a low-temperature heating system, typically operating at supply temperatures between 28-35°C. Supplying such temperatures to radiators is generally not feasible. This gives underfloor heating an advantage over radiators in terms of operational economy (though not necessarily when comparing installation costs). It is definitely worth investing in underfloor heating if you are building a new house and planning to use a heat pump. Over the years, this investment will undoubtedly pay off.
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