Saving on Utilities in Rental Properties: Energy Efficiency Labels, Insulation Ratings, and How to Pick Homes That Cut Bills by ¥30,000+ a Year

Since April 2024, displaying building energy efficiency ratings (BELS: Building Energy Labeling System) on real estate portal sites has become mandatory. By understanding this system, you can identify energy-efficient rentals with lower utility costs before committing to a lease. This is your complete guide to choosing energy-efficient rental homes.

What Is BELS?

BELS is a system that rates a building's overall energy efficiency on a scale of ★1 to ★5. A ★5 rating means "top-tier energy efficiency," while ★1 means "below standard." When you view property listings on real estate websites, this star rating is now displayed.

★5 properties—known as ZEH (Net Zero Energy Houses)—feature solar panels and high insulation, with primary energy consumption close to zero annually. ★4 properties have excellent insulation and reduce utility bills by 30% or more per year. ★3 properties are at the level of typical new-build homes, offering 10–20% utility savings.

★2 and below ratings mean the property meets building codes but offers minimal energy-saving benefits. Most rental properties over 25 years old fall into this category.

Assessing Insulation Ratings — The Real Differences Between Grades 4–7

Equally important as BELS is the insulation rating. In 2022, insulation ratings expanded from a 4-grade to a 7-grade system, allowing more detailed classification.

Grade 4: This was the "highest grade" until 2022 but is now considered "average" as of 2026. Walls, windows, and floors meet baseline insulation standards, but pale in comparison to the latest energy-efficient homes. Properties around 10 years old typically reach this level.

Grade 5: Grade 5 is 20% more efficient than Grade 4, with noticeably lower winter heating costs. Most new-build properties since 2022 aim for this level. Expected annual utility savings: around ¥10,000–¥15,000.

Grade 6: Grade 6 is 25% more efficient than Grade 5, using the latest high-performance insulation materials, triple-glazed windows, and exterior insulation. Expected annual utility savings: ¥20,000–¥25,000.

Grade 7: Grade 7 approaches Passive House standards with ultra-high insulation, where winter heating is barely needed. However, this grade is virtually non-existent in rental properties and limited to a few new-build demonstration homes.

Comparing Grade 4 and Grade 6, the difference in winter heating costs is ¥1,500–¥2,000 per month, or ¥20,000–¥25,000 annually. In many cases, choosing a higher-grade property is worthwhile even if rent is ¥1,000–¥2,000 higher per month, as lifetime savings outweigh the extra rent.

How to Read Primary Energy Consumption

The basis for BELS ratings is "primary energy consumption," measured in MJ/year (megajoules). The lower this number, the lower your utility bills.

As a general rule, 200 MJ/year or below indicates an energy-efficient property, while 150 MJ/year or below suggests high insulation. BELS ★4 properties typically use 150–200 MJ/year, and ★5 properties use 100 MJ/year or less.

However, "primary energy" calculations include generation losses, so they don't directly correlate with actual utility bills. Use this as a reference only; assess actual heating and cooling costs separately based on the building's insulation grade and sunlight exposure.

Key Energy Efficiency Metrics for Choosing Rentals

What to prioritize depends on climate and location.

In northern Japan (Hokkaido and Tohoku), insulation is the top priority. Winter heating costs can reach ¥100,000–¥150,000 annually, so Grade 5+ insulation saving ¥30,000–¥40,000 yearly is significant. Even if rent is ¥2,000 higher monthly (¥24,000 annually), the utility savings (¥30,000–¥40,000) outweigh the increased rent.

In southern Japan (Kyushu and Okinawa), heat-blocking performance is the priority. Focus on reducing summer cooling costs. South-facing units with deep eaves that block daytime sun exposure or properties with heat-reflecting window films offer the biggest cooling savings.

In eastern Japan's major cities (Tokyo, Osaka, Nagoya), balance both heating and cooling efficiency. With BELS ★4 or better, expect ¥20,000–¥30,000 in annual utility savings year-round.

Practical Window Assessment Tips

Even for properties without BELS certification, you can gauge energy efficiency by examining the window type.

Single-pane windows (typical of older properties): Offer zero insulation; winter outdoor temperatures transfer directly indoors. Don't expect utility savings.

Double-pane (double-glazed) windows (standard in new builds): An air gap between two glass panes provides significantly better insulation than single-pane. Most properties under 10 years old have double-pane windows.

Low-E double-pane windows: Special coating reflects infrared radiation, preventing indoor heat loss in winter and blocking external heat in summer. Most Grade 5+ properties use these, though they look identical to standard glass.

Triple-glazed windows (3-layer glass): Used in high-insulation properties in northern Japan, offering ~30% better insulation than double-pane. Rare in rentals, though.

During viewings, check whether windows are double-pane and whether the frames are aluminum or plastic. This tells you quite a bit about the home's energy-efficiency level.

Real-World Utility Savings Comparison

Let's compare two properties: both 1K studios in Tokyo with ¥100,000 monthly rent.

Property A: 15 years old, BELS ★2, single-pane windows Winter heating: ¥8,000/month (Jan–Feb), year-round utilities: ¥6,500/month Annual utility cost: ~¥78,000

Property B: 3 years old, BELS ★4, Low-E double-pane windows Winter heating: ¥5,000/month (Jan–Feb), year-round utilities: ¥4,500/month Annual utility cost: ~¥54,000

The difference is ¥24,000 annually. Even if Property B's rent is ¥1,500 higher per month (¥18,000 yearly), the ¥24,000 utility savings more than offset this, netting ¥6,000 in total savings.

Benefits of Solar Panels and EV Charging Stations

Starting in 2026, more rental properties are adding solar panels and EV charging stations. With solar panels, you can nearly self-generate daytime electricity, saving ¥3,000–¥5,000 monthly on power bills.

However, confirm the contract terms: Does it allow you unlimited use of solar-generated power, or must you return the generated electricity to the landlord? The former offers significant savings.

Energy-Efficient Rental Checklist

Here are key items to verify during property viewings:

1. Is the BELS rating ★3 or higher? Search the property number on your phone and check the portal site.
2. Are the windows double-pane, preferably Low-E coated? Observe the light reflection to assess the glass type.
3. Is insulation visible on the exterior walls? For renovated properties, check pre-renovation photos.
4. What type of heating and cooling? One AC unit? Underfloor heating? Panel heater? This impacts energy efficiency.
5. Any signs of condensation? Condensation marks on window frames or walls suggest poor insulation.
6. Can the landlord show previous tenants' utility bills? This is the most direct assessment method.

Summary

With BELS labeling now mandatory, identifying energy-efficient rentals is easier than ever. Properties meeting the criteria—BELS ★3+, Grade 4+ insulation, and Low-E double-pane windows—can save ¥20,000–¥40,000 annually on utilities, making a significant lifetime difference. When choosing your next rental, factor in energy efficiency alongside rent as a critical decision criterion.

Learn how to leverage Japan's building energy efficiency labeling system, which began in 2024, when searching for a rental. This guide covers how to read energy efficiency ratings, their impact on utility costs, and key points to check during property viewings.