Eco Niwas Samhita: India's Energy Code for Homes

Most conversations about efficient homes jump straight to the air conditioner. Eco Niwas Samhita (ENS) — India's residential energy code, from the Bureau of Energy Efficiency — takes the smarter view: get the building itself right, so it needs far less cooling in the first place. By setting limits on how much heat a home's envelope may admit, ENS quietly makes houses cooler, more comfortable, and cheaper to run — before any HVAC is chosen. For anyone designing or building a home, it's both a code to meet and a blueprint for a better house. This guide explains what ENS requires and why it matters.

It builds on the HVAC Standards & Regulations Guide, part of the HVAC Knowledge Hub.

Scope. This explains ENS to inform understanding and design intent. Compliance is a professional exercise against the version in force and the applicable state rules, confirmed by qualified professionals.

The philosophy: design the load down

ENS is built on the envelope-first principle:

• The cheapest cooling is the heat you never let in. ENS caps how much heat the walls, roof and windows admit, so the cooling load is smaller by design.
• Comfort even without AC — a compliant home stays more comfortable naturally, and where AC is used, it's smaller, cheaper and runs less.
• Focus on the envelope — unlike ECBC (which also covers equipment), ENS for homes centres on the building fabric and passive design, the levers that matter most in residences.

The whole point: a well-designed home does most of the work, and the HVAC just tops it up.

What ENS requires

ENS sets performance limits on the parts of a home that admit heat and light:

• RETV (Residential Envelope Transmittance Value) — the headline metric: a single number capturing how much heat the walls and windows (the non-roof envelope) let in, per unit area. ENS caps RETV (a commonly cited limit is around 15 W/m² for most climate zones) — lower is better, achieved through insulation, shading, better glass and sensible window sizing.
• Roof thermal transmittance — a separate, strict U-value limit for the roof (the biggest heat source in India), pushing roof insulation and cool roofs.
• Window-to-Wall Ratio (WWR) & glazing — limits on glass area and its properties (U-value, solar heat gain), because glass is the weak point for heat gain.
• Natural ventilation & daylight — minimum openable area for cross-ventilation and adequate daylight, so homes can stay comfortable and lit passively (see passive cooling).
• Climate zones — limits vary across India's climate zones (hot-dry, warm-humid, composite, temperate, cold), tuned to each.

Meet these and the home is fundamentally cooler and cheaper to run — code as good design.

Why it matters — even beyond compliance

• Lower bills for life — a low-RETV, well-roofed home needs a smaller AC that runs less, saving every summer for the building's life.
• Comfort without dependence — better passive performance means more hours comfortable without the AC on.
• The right order of design — ENS enforces the correct sequence: envelope first, then HVAC (sizing follows), which is how efficient homes should be designed regardless of code.
• Scale impact — with India adding enormous housing stock, ENS locks in efficiency across millions of future homes.
• Adoption — like other codes, ENS becomes mandatory as states adopt it; even where voluntary, it's an excellent design brief.

The one-line answer

Eco Niwas Samhita (ENS) is India's residential energy code, from BEE, built on the envelope-first idea: rather than starting with the air conditioner, it limits how much heat a home's fabric admits so the cooling load is small by design — cheaper cooling, more natural comfort. Its headline metric is RETV (Residential Envelope Transmittance Value) — a single number for how much heat the walls and windows let in, capped (commonly around 15 W/m²) and lowered through insulation, shading, better glass and sensible window sizing — alongside a strict roof U-value limit (the roof being India's biggest heat source), window-to-wall-ratio and glazing limits, and minimums for natural ventilation and daylight, all tuned by climate zone. It matters beyond compliance because a low-RETV, well-roofed home needs a smaller AC that runs less, saving every summer for the building's life, and it enforces the right design order — envelope first, then HVAC. Becoming mandatory as states adopt it, ENS is both a code and a blueprint for cooler, cheaper Indian homes.

Where to go next

• The framework: HVAC Standards & Regulations Guide.
• The commercial equivalent: ECBC Compliance Guide.
• The physics behind it: Heat Transfer in Buildings · Passive Cooling Guide.
• Then size the HVAC: Cooling Load Calculation Guide.

References

• Bureau of Energy Efficiency (BEE) — Eco Niwas Samhita (Energy Conservation Building Code for Residential Buildings), including the RETV method: https://beeindia.gov.in/
• National Building Code of India, SP 7 : 2026 (current edition), Bureau of Indian Standards; state ENS notifications.
• ISHRAE & building-science references on residential envelope performance and passive design for Indian climates.

This guide informs understanding and design intent. ENS compliance is a professional exercise against the version in force and applicable state rules. Verify current applicability and limits before relying on them.