Radiant floor: real efficiency vs. installation cost

Radiant floor: the efficiency that isn't always cheap

The cheapest kilowatt-hour for heating doesn't come from the most modern system, but the humblest. An energy-saving calculation places natural gas at 0.057 €/kWh with taxes, tied with pellets and below fuel oil (0.068 €/kWh) and electricity (0.1644 €/kWh). Radiant floor, presented as the most efficient solution, lacks a figure: no one has put a cost per kilowatt-hour on the table to back it up. And that's where the problem begins.

How much does it cost to heat a home by fuel type

The comparison breaking down costs lists electricity at 0.1644 €/kWh after adding the 5.11% electricity tax and VAT; heat pumps around 0.047 €/kWh; fuel oil at 0.627 €/L with an estimated boiler efficiency of 90%, leaving the kilowatt-hour at 0.068 €; pellets at 0.057 €; and natural gas, with TUR 2 tariff, at 0.04438175 €/kWh before taxes and 0.057 € after. Radiant floor with a heat pump appears without a number, described as 'the most efficient' for distributing heat evenly.

The first serious response to that table isn't long in coming: radiant floor 'is not profitable at all in a very cold city.' The person arguing this has relatives 200 meters from their home with this system, and they pay a fortune. The nuance matters: if the floor is wood or laminate, which acts as an insulator, thermal efficiency is lost because heat doesn't escape into the air. The system doesn't fail; what's underneath it does.

Thermal inertia: the Achilles' heel of radiant floor

The most repeated argument against radiant floor isn't the fuel price, but time. It has huge thermal inertia: it takes a very long time to heat up. For someone who leaves home at 7 a.m. and returns at 7 p.m., turning it on is an exercise in faith. Conventional radiators, which work at high temperatures, heat up faster. Radiant floor, at low temperatures, heats better but slower.

Some add another layer to the problem: losses. Heating the water, then the floor, then the air, and finally the walls implies a chain with losses at each step. A calculation circulating in the discussion claims consumption is 'nonsense' for this reason. The technical defense is that in single-family homes, losses aren't that high if multiple floors are heated simultaneously and everything remains inside, without exterior walls dissipating heat.

Insulation emerges as the decisive factor. With an A or B energy rating, any system is cheap. Without it, neither radiant floor nor anything else saves the bill. In the past decade, housing in the PAUs (Public Assistance Housing) of northern Madrid was built with E and F ratings and radiant floor: a disaster for those who bought them, ripped off on land price, materials, and insulation.

The detail almost no one looks at: insulation under the floor

All radiant floor is installed on boards with studs providing about 2 centimeters of insulation. This isn't enough. At least 8 centimeters are needed, or half the heat goes to the floor below or the street. It's an installation detail rarely appearing in quotes that decides whether the system saves or wastes.

Usage weighs as much as technique. A high-inertia system like radiant floor works if kept on continuously, with gentle variations. Programming it like a stove guarantees waste. The paradox is that the most efficient system in theory demands a usage discipline many households lack.

Is it cheaper to heat at night than during the day?

No. The idea that turning on heating at night saves money because outdoor temperatures are lower circulates in discussions, and physics debunks it. Losses depend on the thermal gradient between inside and outside: the colder it is outside, the more heat escapes, and the more energy is needed to maintain the same temperature. Heating at night, with the outside colder and occupants in bed, is the opposite of saving money.

The misunderstanding is supported by a broader urban legend: that it's better to keep heating on constantly than to turn it off and on. The numbers say otherwise. It's more profitable to turn it off when no one is home and at night. Radiant floor, due to its inertia, complicates this strategy: turning it off and on has a higher cost than in a fast-response system.

The trap of electricity prices

The discussion shifts to the real price of the kilowatt-hour of electricity in a time-differentiation tariff. A detailed calculation, using official CNMC data for the period November 2014-November 2015 and tariff 2.0 DHA, gives an average of 0.063550 €/kWh during off-peak hours. Applying the 5.113% electricity tax and 21% VAT, it comes to 0.08083 €/kWh. The figure of 0.045 €/kWh defended elsewhere in the exchange doesn't match these numbers.

The complete breakdown, with the tax formula applied step-by-step, is in the original material and reveals a difference that disconcerts those who believed night electricity was almost free. The practical conclusion: neither radiant floor nor any system saves the bill if the price per kilowatt-hour paid isn't the one believed.

---

With these premises, the question isn't which system is more efficient on paper, but how many homes can afford the one that wins in comfort. Radiant floor does that. It also requires construction, insulation, and a usage discipline not everyone has. Is it worth paying for installation to save on the bill, or is the real savings in insulating the house and choosing the cheapest fuel?