How Windows Affect Electricity Bills in Spain
· María Fernández · Energy efficiency and savings · 10 min read
The average Spanish family pays €80-250 per month in electricity, and up to 40% of this goes toward heating and air conditioning. The right windows can cut this expense in half. We’ll break down how window characteristics affect bills and when investments in energy efficiency pay off, using real figures.
Why money goes through windows
Windows are the weakest link in a home’s thermal insulation. A square meter of insulated wall has a U-value of approximately 0.3 W/m²K, while a standard window with single-glazed windows has a U-value of 2.8 W/m²K. This means that a window loses 9 times more heat or cold than the same wall area.
In a typical 80 m² Spanish apartment, windows take up 10-12 m²—that’s only 15% of the external wall area. But this 15% accounts for up to 50% of all heat loss in winter and heat gain in summer. Old aluminum windows without thermal breaks, found in half of Spanish homes built before 2000, are practically holes in the wall in terms of energy efficiency.
The Spanish climate is deceptive. Yes, temperatures of -20°C are rare here, but that’s precisely why many houses are built without serious insulation. When nighttime temperatures in Madrid reach +2°C in the winter, and the central heating is poor or nonexistent, you have to turn on electric heaters. These consume 1.5-2 kWh and can run up your bill by €200-300 per month.
In the summer, the situation is even worse. A 3.5 kW air conditioner in a living room with poorly maintained windows runs 10-12 hours a day, consuming 25-30 kWh per day. At an electricity price of €0.20 per kWh (peak tariff), that’s €5-6 per day for just one room. Over the three summer months, the bill adds up to €450-550.
How Different Window Types Affect Costs
Let’s calculate the cost of a typical 80 m² apartment in Madrid with six windows totaling 10 m². The baseline heating and air conditioning costs with old aluminum windows are approximately €1,200 per year.
Old aluminum windows without a thermal break (U-value = 5.7 W/m²K) are the baseline scenario. In winter, so much heat escapes through these windows that the temperature near them is 5-7 degrees lower than in the center of the room. In summer, the frames heat up to 50°C and radiate heat inward even at night.
Simple PVC windows with double-glazed windows (U-value = 2.8 W/m²K) reduce heat loss by half. Savings on heating and air conditioning will amount to €300-400 per year. The cost of replacing all windows is approximately €3,000-4,000. The payback period is 8-10 years.
PVC windows with energy-efficient double-glazed windows (U-value = 1.3 W/m²K) and a Low-E coating and argon reduce costs by €500-600 per year. The investment is €4,500-5,500, with a payback of 7-9 years.
Premium triple-glazed windows (U-value = 0.7 W/m²K) save €600-700 per year. However, they cost €7,000-9,000 per apartment, so the payback period is 11-13 years. They are suitable for colder regions or when building a passive house.
The double-glazed unit is the key to energy savings
80% of a window’s surface area is glass, so the double-glazed unit determines energy efficiency. The difference between standard and energy-efficient glass can be €100-€150 per year in electricity bills for a single room.
Single-glazed unit (4-16-4 mm) is the minimum standard in Spain. Two panes of glass with a 16 mm air gap produce a U-value of approximately 2.8 W/m²K. Suitable for unheated spaces or the mild climate of the Canary Islands.
Double-glazed unit (4-12-4-12-4 mm) with three panes of glass and two chambers reduces heat transfer to 1.9 W/m²K. This is the optimal choice for most regions of Spain. It adds €40-€60 per m² to the cost of the window.
Low-E coating is an invisible metal coating on glass that reflects thermal radiation. It keeps heat out of the home in winter and keeps heat in in summer. It reduces heat transfer by 30-40%. It adds €30-50 per square meter to the price of a double-glazed window.
Gas filling with argon or krypton instead of air improves insulation by 10-15%. Argon costs an additional €20-30 per square meter and pays for itself in 3-4 years. Krypton is 10 times more expensive and is used only in the premium segment.
A warm spacer between panes of plastic instead of aluminum prevents cold bridges around the perimeter of the double-glazed window. It reduces condensation and saves an additional 3-5% on heat. It costs €10-15 per square meter.
Solar control properties — a Spanish specialty
In Spain, sun protection is as important as thermal insulation. The right solar control glass can reduce air conditioning loads by 40% and save €200-300 per summer.
The solar factor (g-value) indicates how much solar energy passes through the glass. Standard glass has a g-value of 0.85 (transmits 85% of solar heat). Solar control glass with a g-value of 0.40 transmits only 40%, but remains visually clear.
Selective glass is a compromise between heat protection and natural light. It transmits visible light (60-70%) but blocks infrared radiation (up to 80%). Ideal for south-facing facades, it costs €60-80 more per square meter than standard glass.
Tinted glass is cheaper (an additional €30-€40 per m²), but it darkens the room. It’s suitable for offices and sunny bedrooms, but can create a gloomy atmosphere in the living room.
Electrochromic glass changes its transparency on command. In the morning, it’s clear for maximum light, and during the day, it’s darkened to protect from heat. It costs from €800 per m² and remains uncommon, but is gaining popularity in the premium segment.
The Role of the Frame in Energy Saving
Although the frame occupies only 20-30% of the window area, it can be a weak point in thermal insulation. An aluminum frame without a thermal break becomes coated with condensation in winter and acts as a reverse radiator, cooling the room.
PVC profiles with 5-6 chambers provide a frame U-value of 1.0-1.2 W/m²K. The more chambers, the better the insulation, but the profile becomes wider. The optimal width for Spain is 70-80 mm.
Thermal-break aluminum has a 20-35 mm wide plastic insert that interrupts heat transfer. The U-value of such frames is 1.5-2.0 W/m²K. The wider the thermal break, the better the insulation and the higher the price.
Wood is a natural insulator with a U-value of 1.3-1.6 W/m²K. However, it requires protection from the Spanish sun and regular maintenance. Wood-aluminum windows combine good insulation with minimal maintenance.
Ventilation and airtightness - a balance is important
Windows that are too tightly sealed without proper ventilation lead to stuffiness, condensation, and mold. But every gap is a waste of energy and money.
The air permeability class indicates how airtight a window is. Class 4 (maximum) allows less than 3 m³/h of air per m² at a pressure difference of 100 Pa. For Spain, Class 3 is sufficient; otherwise, forced ventilation is required.
Supply air valves in frames provide controlled airflow without opening the windows. They allow 5-40 m³/h of airflow, depending on the pressure difference. They cost €80-€150 per valve but prevent stuffiness and condensation.
Microventilation allows a 3-5 mm gap with a specific handle position. Provides minimal air exchange with only 5-10% heat loss compared to a fully open window. This feature adds €30-€50 to the cost of the hardware.
Automation for Maximum Savings
Smart windows and sun protection systems can save an additional 15-20% on climate control.
Automatic roller shutters with sun sensors lower when the sun shines directly into the windows and raise on cloudy days to maximize natural light. Savings of up to €100 per year on air conditioning are possible. The system costs €500-€800 per window.
Window sensors, linked to the climate control system, turn off the air conditioning or heating when the window is open. They prevent energy loss due to forgetfulness. Cost: €50-€100 per sensor.
Programmable blinds between the panes of glass with electric drive can be set to close automatically during the hottest hours. Smartphone control allows you to prepare your home for your return by closing the blinds during the day and opening them in the evening for natural cooling.
Real-World Case Studies and Payback Calculations
Apartment in Barcelona, 90 m², south-facing Replacing 8 old aluminum windows with PVC windows with selective glazing:
- Investment: €5,500
- Air conditioning savings: €400/year
- Heating savings: €200/year
- Payback: 9 years
- Additional bonus: 15 dB reduction in street noise
Townhouse in Madrid, 150 m², all directions Complete replacement of 15 windows with energy-efficient ones and automation:
- Investment: €12,000 (windows) + €3,000 (automatic blinds)
- Annual savings: €1,200-1,500
- Payback: 10-12 years
- Property value increase: 5-7%
Villa in Malaga, 200 m², panoramic windows Replacing sliding doors to a terrace (20 m²) with lift-and-slide windows with solar control glass:
- Investment: €18,000
- Air conditioning savings: €800-1,000/year
- Payback: 18-20 years
- However, the comfort and aesthetics justify the investment.
Government Programs and Subsidies
Spain actively supports energy-efficient housing renovation. The PREE 2023-2025 program offers subsidies for window replacement.
The basic subsidy is 40% of the cost of the work for the main residence. Maximum: €3,000 per residence. The requirement is a minimum 30% improvement in energy efficiency.
Additional 20% for households with an income below 3 IPREM (approximately €2,000/month per family). This means the total subsidy can reach 60%.
Tax deductions of up to 20% of energy efficiency investments (maximum €5,000/year). Applies to expenses not covered by subsidies.
Contractor requirements — the work must be carried out by a certified company with a minimum 3-year warranty. An energy audit is required before and after installation.
Myths about Windows and Electricity
“It’s warm in Spain, so energy-efficient windows are unnecessary” — the most expensive myth. Due to the lack of central heating in many regions and the extensive use of air conditioners, windows have an even greater impact on costs than in northern countries.
“It’s enough to install blinds” — blinds help, but the heat has already passed through the glass and warmed the air between the blinds and the window. This hot air still warms the room. External blinds are three times more effective than internal ones.
“Triple glazing is always better” — in most regions of Spain, triple glazing is unnecessary. It’s heavier, more expensive, and lets in less light. High-quality double glazing with Low-E and argon offers the best price/performance ratio.
“The tighter, the better” — without proper ventilation, super-tight windows will lead to stuffiness and mold. The balance between insulation and air exchange is critical for a healthy indoor climate.
Step-by-step savings plan
Conduct an energy audit — This will reveal your actual heat loss and savings potential.
Start with the worst windows — if your budget is limited, replace the most problematic windows first (usually large windows on the south and west sides).
Choose the right glass for each direction – solar control for south and west, neutral for north, and selective for east.
Don’t forget about installation – 30% of efficiency is lost with poor installation.
Add automation gradually – first roller shutters in the bedrooms, then sensors and smart controls.
Take advantage of subsidies – the paperwork takes time, but the savings are significant. Many installers help with the paperwork.
The right windows are an investment that works for you 24/7 for 30-40 years. Every euro saved on electricity bills is not only money in your pocket but also a contribution to the fight against climate change. With the current rise in electricity prices, the payback period for energy-efficient windows is only accelerating.
