12 August 2026 · 3 min
The Arithmetic Behind 48 Euro a Month
How thermal calculations, a 7.08 kW photovoltaic array and a well dug into the Tuscan earth add up to a monthly energy cost the size of a phone contract.
Domus Sapientes editorial team, with technical supervision by Tombari Costruzioni · Articles are drafted with the help of AI tools and reviewed by the team before publishing. Every technical claim is checked against the project specification.
Every house has an energy bill. It arrives once a month and shows what it cost to stay warm in January and cool in August. At Bosco Orizzontale we would rather you asked about ours. From the thermal calculations for the project, it is about 48 euro a month.
Four services, one figure
The figure covers heating, air conditioning, domestic hot water and controlled mechanical ventilation. Those four are the basic energy needs of a household, the things a family pays for whether it thinks about them or not. In each villa they are delivered together, by one integrated set of systems, and their combined projected cost is about 48 euro a month, roughly the price of a dinner for two.
Where the number comes from
The number was produced by thermal calculation, the standard engineering method used to model and certify buildings in Italy. Each villa is designed as a Nearly Zero Energy Building in design energy class A4, the highest class the Italian scale recognises. Its global non-renewable energy performance index is 14.59 kWh per square metre per year. That figure deserves a moment. Spread across roughly 200 square metres of villa, it describes an annual energy demand small enough for modest equipment to satisfy. Here is the whole arithmetic in one sentence: the bill is small because the demand is small. Breathable hemp-lime walls, wood-aluminium windows and Griesser solar screens on every frame keep heat where it belongs in each season, so the systems have very little left to do.
The machinery of a small bill
What remains is handled by equipment chosen to work together. In the TOP version, a 7.08 kWp photovoltaic array on the roof turns Tuscan daylight into electricity, and a 15 kWh battery holds the surplus for the evening. The same electricity heats the domestic hot water, held in a 300-litre tank. The LIGHT version has ten modules, 5.90 kWp with an inverter and no battery. Below the garden, a Canadian well, a surface geothermal system, draws incoming air through the ground, where the temperature stays steady all year, warming it before winter mornings and cooling it ahead of summer afternoons. The controlled mechanical ventilation then carries that air through the house, passing the outgoing flow across an integrated heat exchanger so the warmth already inside stays inside. On the first floor, the bioclimatic greenhouse collects solar radiation in autumn and winter and feeds warm air into the same ventilation circuit, a contribution that costs nothing to run. Each element is ordinary engineering. The result comes from the way they are stacked.
An honest caveat
About 48 euro a month is a projection, and it should be read as one. It comes from the energy report required under Legge 10, at the price per kWh of about two years ago, and it holds for both TOP and LIGHT. Thermal calculations assume standard conditions, and households are never standard. Real consumption will move with the number of people in the house, the temperatures they prefer, the length of their showers and the character of each winter. What the calculation establishes is the scale, and the scale is what separates these villas from most of the housing stock around them. A typical older home works against itself: uninsulated walls, ageing glazing, a boiler burning fuel to replace heat that the envelope loses as fast as it arrives. Owners of such houses plan their years around the heating season. Here, the heating season barely registers.
The three villas of Bosco Orizzontale stand in Borgo a Buggiano, in the Valdinievole, a short drive from Montecatini Terme. The thermal calculations stand behind every figure, and so does the house they describe. The project is at www.domussapientes.it. Come and see it breathe.
Curious how this reads in a real house?
Three hemp and lime villas in Borgo a Buggiano, under construction, three available. The specification and the reserved price list arrive within 24 hours to anyone who requests them.
Compare TOP and LIGHT