The most efficient heating System

The most efficient heating System

The most efficient heating systems significantly determine the attainment of an appropriate temperature in our homes or workspaces. However, not all systems are equal in terms of efficiency and energy savings.

Winter is looming, and in most Spanish households, especially in the northern part of the peninsula, we’re already starting to switch on the heating. According to the INE National Statistics Institute, 8 out of 10 homes are equipped with some form of heating system. However, this proportion varies significantly based on the climatic conditions of each autonomous region.

Regions in northern Spain and inland communities like Castilla, León, Madrid, Aragón, and Castilla-La Mancha surpass the average in heating system usage due to their colder temperatures. Conversely, in the warmer areas of Spain, such as the Canary Islands, Extremadura, and Andalucía, there are barely any heating systems installed. The most efficient heating systems significantly determine the attainment of an appropriate temperature in our homes or workspaces. However, not all systems are equal in terms of efficiency and energy savings.

Table of Contents

Options for Heating

These days, there are numerous options to heat or cool a home. Referring back to the National Statistics Institute (INE), it indicates that natural gas is the most common system, present in 40% of Spanish households, followed by electricity, used in 34% of Spanish homes. Then, there’s a shift to petroleum derivatives like butane gas, propane, or diesel.

Heating systems utilizing biomass, aerothermal, and geothermal sources are less common. However, they’re increasingly valued for their efficiency and sustainability. Each heating system type has its advantages and disadvantages, much like everything in life, with differences in terms of costs and efficiency. The choice depends on individual needs, housing characteristics, and location, as detailed below.

Types of Heating

Various heating systems are available in Spain, and it’s essential to consider that some systems may require significant alterations to the building’s structure. Thus, in a communal building, they might not be feasible.

Gas Boiler Heating

This system is most prevalent in Spanish homes, especially in colder regions. It operates by using natural gas or diesel to heat water in a boiler, which is then distributed through radiators, underfloor heating systems, or hot air ducts to provide warmth to the residence.

In this system, the boiler is crucial as not all boilers are the same, varying in both power and type. These factors determine the level of thermal comfort achievable for the home generally, higher kilowatt (kW) power results in greater heat capacity from the system. Condensing boilers increase system efficiency, significantly impacting energy consumption.

Electric Heating

Following gas, electric heating is the second most utilised system in Spain. It requires minimal maintenance and installation but may not be the best choice for homes in icy areas. Within this category, there are several types:

  1. Electric radiators or storage heaters store heat and release it gradually. They don’t require installation as they plug directly into electricity sockets, providing decent heat output.
  2. Underfloor heating, placed beneath the house’s flooring, is slightly more expensive to install but offers a pleasant heating experience.
  3. Oil-filled electric radiators operate automatically without installation; they plug directly into electricity sockets.
  4. Electric convection heaters generate heat as they consume energy, quickly heating a room.

Heat Pump Heating

We’ll delve deeper into this system later, but for now, it’s worth mentioning that heat pump heating, commonly known as reversible air conditioning, can provide both warmth and coolness. It’s an attractive option in areas with mild winters or smaller open-space homes.

Renowned for its high energy efficiency, it requires minimal electricity to generate heat. However, it’s crucial to note that warm air tends to dissipate relatively quickly.

Biomass Heating

Biomass stoves are an excellent choice for larger single-family homes in regions with long, cold winters. They function similarly to gas boilers. This heating system is economical and environmentally friendly, utilizing fuels derived from forest waste and non-human-consumable crops. Biomass is compacted into blocks or pellets and, when burned, emits certain pollutants, offset by the CO2 absorbed during its lifecycle.

Biomass Heating

Aerothermal Heating

A highly efficient system harnessing ambient air heat for heating and, in some cases, cooling. Regarded as ecologically sound due to minimal CO2 emissions, it conserves energy by requiring very little electricity. Aerothermal heating can also heat domestic water, adding to its versatility. Despite a higher initial investment compared to many systems, it proves cost-effective in the long run, especially in comparison to gas heating.

Solar Heating

Solar heating systems capitalize on solar radiation, converting it into usable heat for buildings and domestic water. The energy can be sourced from:

  • Photovoltaic solar panels that power electric heating systems or other household electrical devices.
  • Thermal solar panels that capture solar radiation, converting it into thermal energy as heat but don’t produce electricity.

Both cases involve an initial investment that can be profitable for larger homes, especially when the panels serve multiple purposes like providing electricity alongside heating, as with photovoltaic panels.

Which Heating System Is Most Economical Long-Term?

In the long term, the most cost-effective options are solar energy and aerothermal heating, including biomass, geothermal, and solar power.

  • Aerothermal heating is the most affordable in terms of installation and is highly recommended for homes across Spain.
  • Despite higher initial costs, biomass and geothermal systems can be profitable investments in larger buildings, whether new constructions or refurbished ones.

Consider that solar heating depends on available space in the garden or on the house’s roof and the solar radiation in the area. In low-sunlight regions, it’s advisable to have an additional electrical energy source.

In Warm Climates and Second Homes

In places like the southern or eastern regions of Spain where heating is occasional or in second homes, it’s a misconception that investing in an expensive heating system isn’t worthwhile. With rising energy prices, having an efficient, low-maintenance heating system becomes necessary, especially during two to three months when winter temperatures might drop just above zero.

Electric heating has been recommended for such cases due to its low initial investment. However, fluctuations in electricity prices should be considered. Installing a good heat pump is advised, as its efficiency can make it competitive, not just for heating but also for cooling in summer.

For Cold Climates and Homes without Major Reforms

Gas heating offers high thermal comfort with a reasonable initial investment, facilitating mid-term amortization. It’s programmable and room-regulated, contributing significantly to energy savings. However, like electricity, gas prices fluctuate in a changing market affected by global political shifts.

Gas heating requires annual maintenance for optimal and safe operation. Additionally, gas prices are linked to electricity, leading to price fluctuations monthly.

Heating Systems in Existing and Old Buildings

Sooner or later, residents in an old building contemplate how to effectively modernize their outdated heating systems. Even owners of newer buildings may find heating system upgrades intriguing. There are numerous reasons to consider installing a new heating system in an old building, yet many owners are deterred by high investment costs. At Pacheco & Associates Architects, we address fundamental questions regarding the modernization of heating systems in old buildings.

When Is a House Considered an Old Building?

Initially, many owners aren’t sure if their dwelling qualifies as an old building. Providing a general definition for an old building is challenging due to considerable differences in structure, materials, and internal layouts among buildings of varying ages.

To offer practical guidance for system owners, our definition of an old building is based on pragmatic considerations. We also include some existing modern buildings within the category of old buildings. Therefore, if contemplating heating system modernization and not residing in a newly constructed building, our guide will still provide valuable insight.

Which Regulations Apply to Old Oil and Gas Boilers?

Many Spanish households still use oil or gas heating systems, something that will be prohibited starting in 2035. The European Union passed a resolution last March setting an end date for diesel and gas boilers in residences.

Anyone considering renovating the heating system in an old building still has freedom of choice among all heating technologies and fuels until 2026. From 2026 onwards, new installations of diesel heating systems will only be possible as hybrid systems, integrating renewable energies. However, exceptions exist for existing buildings, such as when a gas connection isn’t feasible.

Beyond these obligations, before purchasing a heating system, aspects like fire safety in the boiler room, in consultation with a heating contractor and responsible combustion gas inspector, need consideration. Safety measures when installing a tank should also be taken into account.

What Costs Are Involved in Modernizing Heating Systems in Old Buildings?

Given the significant diversity among old buildings concerning age, location, layout, and whether they’re part of a historic centre, different types and amounts of work are required. To install and operate a new heating system in an old building, updates to facilities, smoke systems, chimneys, and thermal insulation improvements are often necessary. An architect can provide precise details after inspecting the building.

How Can Funding Be Obtained for a New Heating System in an Old Building?

Support for installing renewable energy thermal systems (heating and hot water) in residences is outlined in Royal Decree RD 477/2021. This decree also covers aid for photovoltaic or wind self-consumption and energy storage.

Who Qualifies for government Aid?

For installations that provide heating and hot water use:

  • Solar thermal energy: solar panels for heating water.
  • Biomass: pellet or olive pit boilers and stoves.
  • Heat pumps: air-to-water aerothermal, hydrothermal, or geothermal. This doesn’t apply to air-to-air pumps used in air conditioning units.

Moreover, ensure your installation meets the requirements of the Building Thermal Installations Regulation (RITE). In the case of biomass boilers and stoves, emissions of greenhouse gases must be reduced by at least 80%. These aids are available until 31/12/2023.

How much?

The amount of aid you receive depends on the power of the system you install. For each type of installation, the decree establishes a module, which is the amount allocated per kW of power your appliance has.

To calculate the total potential aid, you should multiply the kW of power installed by this module. However, there are subsidy limits. For instance, for an 8 kW aerothermal heat pump, the aid would be 3,000 euros, as the calculation result would be 8 x 500 = 4,000, exceeding the maximum limit.

Here’s the breakdown of the aid provided per kW and the maximum value for each type of installation:

The grants for installing renewable energy thermal systems (heating and hot water) in homes are defined in Royal Decree RD 477/2021(Real Decreto RD 477/2021) . This decree also encompasses aid for photovoltaic or wind self-consumption and energy storage.

Which new heating system is suitable for your old building?

There isn’t a single answer to this question as numerous factors come into play. Generally, when it comes to upgrading heating systems in old buildings, several heating systems are available to choose from. Innovation and efficiency are crucial; with changes in climate policy, new heating systems should reduce the use of fossil fuels. There are several ways to achieve this.

Not all systems are suitable for every existing building. Depending on the technology used, different requirements must be met. Therefore, it’s essential to clarify some aspects in advance and define your selection criteria. Here, Pacheco Architects explains what to consider before making a decision and which heating systems are most suitable for an old building.

The first consideration is the energy source you’d like to use for heating in the future or how important sustainability and independence from electric supply companies are to you. Additionally, acquisition and operational costs will likely play a role in deciding on a new heating system.

The following heating systems can be considered for a general shift to renewable energy sources:

  • Condensing oil boiler combined with a solar thermal system
  • Condensing gas boiler combined with a solar thermal system
  • Pellet heating system
  • Heat pump
  • Fuel cell
  • Hybrid gas heating

Finding the appropriate alternative to gas heating

The uncontrollable rise in gas prices, coupled with increasing price fluctuations, and the uncertain future of gas heating from a climate policy perspective, have prompted many owners to consider alternatives to their gas heating. In the following guide, we present some possible options for replacing gas heating with a renewable energy heating system. Please note that it’s not possible to provide general recommendations as buildings, local conditions, and individual heating behaviours vary significantly.

Replace your gas heating with a heat pump

Heat pumps are used in both new and existing buildings when replacing a gas heating system. They not only help reduce fossil fuel consumption, thus saving valuable resources and reducing climate-damaging CO2 emissions, but they’re also quiet, cost-effective, and a safe heating system. New heat pumps have been specifically developed for use in existing buildings.

Heat pumps utilize energy already present in the outside air. For instance, if the outdoor temperature is 10ºC, there’s 10ºC available for extraction from the environment. In the process, the pump extracts thermal energy from the air, ground, or groundwater. 

Depending on the heat pump’s specific function, the energy is used to evaporate a refrigerant, which is then compressed and, consequently, heated. Within the closed circuit of a heat pump, this heat is transferred to the heating water, which can be used to heat rooms or for domestic hot water. Unlike gas heating, a heat pump doesn’t require any combustion process. 

Only a quarter of the energy expended needs to be available in the form of electricity. This is crucial to emphasize. Essentially, for every 1kW of energy used, 4kW is extracted. If you wish to entirely eliminate fossil fuels, opting for an eco-friendly electricity tariff or generating your electricity with a photovoltaic system (PV) is advisable. This not only increases your energy self-sufficiency but also minimizes CO2 emissions.

You can continue using existing radiators

There are wall-mounted devices available in the market that save space, along with compact free-standing units with an integrated 190-litre hot water tank. These devices, developed specifically for upgrading heating systems in single-family and two-family homes, operate conventionally with R290 refrigerant (propane), which is extremely climate-friendly compared to refrigerants used in other heat pumps.

This refrigerant enables new heat pumps to reach high flow temperatures of up to 70 degrees Celsius, even when it’s minus 15 degrees Celsius outside. Generally, it’s possible to continue using existing radiators. It’s not essential to install underfloor heating, which helps keep the project’s costs within reasonable limits.

More efficiency, lower costs

By installing a heat pump, you’ll save on heating costs in the long term and protect the environment and climate. As mentioned earlier, a heat pump allows for extremely efficient utilization of ambient energy. This is because the energy available for heating the house and domestic hot water at a comfortable temperature is free and already present in the environment. Before acquiring a heat pump, it’s advisable to get answers to some questions. One of them concerns the type of heat pump.

Types of heat pumps: Compare before you buy

Similar to how “a home” is a generic term encompassing many styles and different models, “heat pump” is a generic term covering heating systems that use the environment as a heat source. Different heat sources and sophisticated technology enable homeowners to find the heating system that suits them best and provides reliable and cost-effective warmth.

The following heat pump comparison offers initial guidance on when it’s worthwhile to invest in a particular type of heat pump. What are the advantages of an air-to-water heat pump, and where might a water/brine heat pump be more cost-effective? You can learn more about the similarities and differences here.

Common Features in All Heat Pumps

As the name implies, this heating system generates heat by pressurizing a gas similar to an air pump. Regardless of the heat source used by the heating system, the refrigerant circuit process is the core of all heat pumps. It collects ambient heat from the air, a geothermal source, or a body of water that can reach the required temperature.

Pipes lead to a heat exchanger through which the refrigerant circulates. Due to the special properties of its material, the refrigerant evaporates at low temperatures. The heat generated in the process is too low for use in heating and domestic hot water, which is where the electrically powered compressor comes into play to raise the temperature.

Differences Between Heat Pumps

Those purchasing a heat pump should familiarize themselves with one of the primary differences between different types: the heat source used. Ultimately, this also determines where the heat pump is installed. In addition to ambient air, extracted air, and groundwater, a heat pump can also extract heat from the ground.

In the case of an ice energy store, all three heat sources can supply the required energy. Which of these heat sources is most suitable depends on individual circumstances. Air-to-water heat pumps are frequently used in practice, partly due to their relatively quick installation. Of course, price also plays a significant role. Ultimately, an air-to-water heat pump is the most economical way to heat using environmental energy.

Calculation of Solar Thermal Systems: Size and Design

You can install a solar thermal system with flat-plate or tube collectors. Vacuum tube collectors are often used when there’s limited space available on the roof. They’re more efficient than flat-plate collectors and have particularly good thermal insulation due to the vacuum.

Another aspect to consider is whether you want to heat only domestic hot water or also assist the heating system. Regardless of your decision, the rest of the system must adapt accordingly. If the system is solely for heating domestic hot water, consider a hot water tank.

This, in turn, influences the collector surface area as well as the tank size, ultimately depending on the number of people living in the household. In any case, the key points are:

  1. Number of people in the home
  2. Size of the residence
  3. Type of collectors
  4. Subsidy conditions
  5. Required coverage
  6. Domestic hot water or central heating support (single-family home)?
  7. In a single-family home = building’s energy status + heat demand
  8. Insulation

Sizing and designing domestic hot water (DHW) using Viessmann panels

This table provides a guide for sizing and designing domestic hot water (DHW) using Viessmann panels, considering the number of occupants and their daily hot water demand at 60°C.

It also outlines the recommended tank volume, the number of collectors from the Vitosol-FM/-F series, and the collector area from the Vitosol-TM series. Here’s a breakdown:

This table offers a guide for sizing hot water systems based on the number of occupants and their daily hot water needs, correlating it with the appropriate tank volume and the number and size of collectors required to meet those demands.

Assumptions for Design: Assuming a consumption rate of 30 litres per person at 60°C. If the per-person consumption is significantly higher, the selection should be based on litres per day.

Standard Value: A family of four requires a collector surface of about five square meters (m²) and a DHW (Domestic Hot Water) accumulator with a capacity of around 300 litres for heating domestic hot water.

Sizing and Design of Central Heating Support: The following sizing table can serve as a guide for supporting central heating.

This excerpt outlines the assumptions for the design criteria, specifying the standard consumption per person and the expected requirements for a family of four in terms of collector surface area and DHW accumulator capacity. It also hints at a table for sizing and supporting central heating systems.

Standard Value: A family of four typically requires a collector surface area of 10 to 12 square meters (m²) and a tank with a volume of 60 to 80 litres per m² as support for central heating.


At Pacheco Architects, we hope this article has been helpful in the process of selecting an efficient heating system for your home or workplace. We trust it has allowed you to compare the different systems available in the market and select the one that best suits your needs.

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