Hydronic heating systems are a highly energy-efficient and sustainable option for indoor thermal regulation, as well as a key lever in decarbonising the built environment.
Hydronic heating is well positioned ahead of sustainable building design trends, as it is inherently more eco-friendly than conventional alternatives.
However, it can be further optimised for maximum sustainability by selecting an appropriately sized system, using high-efficiency heat sources, ensuring proper insulation, combining energy-saving technologies, utilising zoning controls, optimising distribution systems for efficiency, and considering future maintenance needs.
Hydronic systems are a subcategory of radiant heating and cooling technologies that use hot water pumped through internal piping, beneath the floor or within the walls, to thermally regulate indoor environments.
Their key characteristic that makes them highly energy efficient is that heat transfer through circulating water is more effective than through circulating air.
A study conducted at the Lawrence Berkeley National Laboratory showed that radiant heating and cooling systems could lead to energy savings of up to 30 per cent, depending on the climate zone, with greater reductions of up to 42 per cent observed in hot and dry regions.
Significant savings were also demonstrated in cool, humid regions, achieving reductions of 17 per cent.
Water-based (hydronic) radiant systems have three distinct types, according to REHVA (Federation of European Heating, Ventilation and Air Conditioning Associations): radiant ceiling panels, made of suspended metal ceiling panels topped by copper tubing; embedded surface systems, with tubing attached over thinner prefab or in- situ layers; and thermally activated building systems where plastic tubing is built into structural slabs.
Embedded surface systems can also be further divided into five subtypes, based on the pipe location.
As a result of climate initiatives and policy changes stemming from the energy transition, HVAC manufacturers are increasingly providing hybrid solutions that combine boilers with air-to-water heat pumps. This dual-fuel approach features a high-output boiler for colder climates and a heat pump for milder conditions.
Water temperature is crucial to the operation of both boilers and heat pumps, with heat pumps heating water to 60 degrees Celsius, while boilers typically operate at around 80 degrees Celsius.
Survey data indicates that most homes experience peak heating demand for only a short period each year, highlighting the ability of hybrid systems to optimise the energy efficiency of their components based on current conditions.
When considering the broader central heating systems available on the market, hydronic systems stand out as the most sustainable, energy-efficient, and cost-effective option. They operate at low costs and produce very low greenhouse gas emissions, especially when powered by renewable energy. Another major benefit is that they provide optimal comfort levels.
Lance Turner, Technical Editor at Renew (formerly the Alternative Technology Association), explained that hydronic radiator systems offer several advantages over other heating methods. They emit heat either underfoot or near floor level, reducing the need for forced air movement.
“Some more complex hydronic systems have multiple zones, so you can choose to heat only part of the house [and reduce] energy use.
“Disadvantages include the initial installation cost – a complete system can easily cost $10,000 or more, depending on the boiler, the number of circuits, and the type of radiator.
“However, prices have dropped over time as hydronic heating becomes more popular and recent technology in boilers and pipe systems makes it more affordable.”
A study published last year analysed the hydronic systems of 259 buildings across 56 organisations in the United States, generating a dataset that comprised 120 million measurements taken by building automation systems between 2014 and 2024.
For a typical building, the data includes measured supply and return water temperatures, flow rate, output power, system state, and outdoor temperature.
Additionally, pump and boiler data were available for a smaller subset of buildings.
The research aimed to provide valuable insights for operators, designers, owners, and policymakers by emphasising that significant energy-saving opportunities are often available. These can be realised by adjusting the design and operation of hydronic systems based on real-world results.
The findings revealed that many assumptions about the systems did not align with real-world performance, as the systems operated far more frequently than expected, at 81 per cent of hours annually for the median building.
Loads were lower and more skewed than the researchers expected, and oversizing was common even when accounting for redundancy requirements.
They explained: “Load distributions indicate that relatively small equipment could serve a surprisingly large percentage of annual loads.
“Notably, equipment sized to 30 per cent of the maximum measured load could serve up 84 per cent of the total heating energy consumption for the median building.”
Preventing condensation is essential for the safe and efficient operation of hydronic systems. This likelihood can be significantly reduced by maintaining the humidity ratio below 60 to 65 per cent.
The primary strategy for preventing condensation is mechanical dehumidification, which includes liquid desiccant dehumidifiers and ventilation-focused dehumidification methods.
As a secondary strategy, the supply water temperature can be calibrated to remain above the indoor dew point temperature. Regulating the supply of water based on dew point monitoring ensures optimal thermal comfort while preventing condensation.
Tertiary measures include regulating the surface temperature of thermally conditioned ceilings or flooring systems, as well as implementing predictive and pulsating flow control mechanisms. These measures enhance the modulation of water supply, providing additional protection against the risk of condensation.