For decades, the standard European home was defined by white metal radiators and a bulky copper cylinder in the airing cupboard. However, a new wave of “invisible” heating technology is changing how we warm our homes. By combining low-voltage carbon fleece (often referred to as heating mats) with phase-change heat batteries, homeowners can remove visible heating infrastructure entirely while gaining precise control over their energy usage.
Here is how these two technologies work, their installation costs, and what you can expect to pay to run them.
The Invisible Radiator: Low-Voltage Carbon Fleece
Traditional underfloor heating uses water pipes or thick electric cables buried in concrete. By contrast, carbon fleece is an ultra-thin (approx. 0.4mm) mesh containing carbon fibres.
How It Works: The fleece is stapled directly to ceilings or walls, then plastered over. It runs on low voltage (typically 24V or 36V) via a central transformer, making it safe to drill through later without risk of electrocution. When powered, the carbon fibres resist the electricity, generating Far Infrared heat. Unlike standard radiators, which heat the air (convection), infrared travels through the air to warm solid objects—furniture, walls, and people—directly. This creates a sensation similar to standing in direct sunlight on a crisp day.
Installation Costs (Estimated) Because the system requires a transformer and skilled plastering work, it is generally more expensive to install than standard electric radiators but cheaper than a wet underfloor system or heat pump.
Material Cost: Between €40 and €60 per square metre for the fleece itself.
Transformer & Controls: A central transformer unit (essential for the low-voltage safety) can cost between €300 and €800, depending on the total wattage required.
Total Installed Cost: For a standard room (including the electrician and the plasterer to skim over it), expect to pay roughly €80 to €120 per square metre of heated area.
Running Costs: This system is 100% efficient (1 unit of electricity = 1 unit of heat), but electricity is more expensive than gas or heat pump systems.
The Passive Advantage: In a modern, well-insulated home (like a Passive House), these systems are incredibly cheap to run because the building retains the heat. A 100 m², highly insulated home might cost only €400–€600 per year to heat.
The Leaky House Warning: In an older, poorly insulated Spanish apartment, running costs will be high. Without insulation, you could easily spend €1,500+ per year, as the walls will constantly lose the heat the fleece generates.
The Magic Box: Phase-Change Heat Batteries
For hot water, the traditional solution is a large tank heated 24/7. The modern alternative is a Heat Battery using Phase Change Material (PCM).
How It Works: Instead of storing hot water, this box contains a salt-based chemical compound. When you “charge” the battery (using grid electricity or solar power), the chemical changes state from solid to liquid, storing a large amount of latent heat. When you open your hot tap, cold mains water flows through a heat exchanger inside the box. The liquid chemical instantly transfers its heat to the water, cooling back down into a solid in the process. You get mains-pressure hot water instantly, but the box itself contains no water storage to leak or corrode.
Installation Costs (Estimated) These units are compact (about the size of a small dishwasher) and free up valuable cupboard space, but the upfront technology cost is high.
Unit Cost: A unit capable of replacing a standard 200-litre cylinder typically costs between €2,500 and €3,500.
Installation: Installation is simpler than a gas boiler (no flue, no gas pipes), usually costing €500–€800 for a plumber and electrician to fit.
Running Costs
Efficiency: These batteries have very low heat loss. A standard copper cylinder might lose 1.5–2.5 kWh of heat per day just sitting there. A heat battery might lose only 0.5–0.7 kWh per day. Over a year, this saves roughly €100–€150 in “standing losses” alone.
Tariff Smarts: The real savings come from charging the battery during off-peak hours (e.g., 2:00 AM to 6:00 AM) or using free solar energy. If charged purely on cheap overnight electricity, a family of four could spend as little as €25–€35 per month for all their hot water.
Is It Worth It?
This combination (Fleece + Heat Battery) is often called the “All-Electric Future” solution.
Pros: Zero maintenance (no boiler servicing), invisible heating, frees up floor/cupboard space, and silent operation.
Cons: Higher upfront cost than for basic electric radiators, and running costs can be high if your house is poorly insulated.
Verdict: If you are building a new, airtight home or doing a deep renovation with excellent insulation, this system offers superior comfort and minimal clutter. For older, draughty properties, a heat pump may still be the more economical choice despite the higher maintenance.