Lunos e2 Ductless HRV System: Technical Overview, Performance, and Installation Guide

Key Summary

The Lunos e2 is a ductless, wall-through HRV that uses paired fans and a ceramic regenerative heat exchanger to supply and exhaust air in balance. It is engineered for low-energy homes and retrofits where installing full ductwork is difficult, offering high heat recovery efficiency, very low electrical consumption, and quiet operation suitable for bedrooms and living areas when properly designed and installed.

Short and standard tube options allow the system to adapt to different wall thicknesses, from thin retrofit walls to deep, high‑performance assemblies. Understanding its airflow limits, installation constraints, and control strategy is essential to ensure it meets local code requirements and provides effective whole‑house ventilation.

TL;DR

• Lunos e2 is a ductless HRV that works in synchronized pairs, cycling between supply and exhaust to provide balanced ventilation through exterior walls.
• A ceramic regenerative core can reach around 85% heat recovery efficiency under test conditions, with partial humidity recovery that can moderate indoor dryness in cold climates.
• The system’s airflow range is modest, making it best suited to low-load, tight homes or zoned ventilation rather than high‑occupancy spaces with large ventilation demands.
• Short vs. standard variants differ mainly in tube length and fan depth to match different wall thicknesses, with accessories for extra‑long walls and insulated assemblies.
• Power draw is very low (on the order of a few watts per unit at lower speeds), and sound levels are designed to be compatible with bedrooms and living rooms when correctly installed.
• The e2 is designed to meet European building and ventilation standards and is commonly used in low-energy and Passive House projects; U.S. and Canadian users should still verify local code compliance and sizing requirements.
• On an e-commerce site, a product like the Lunos e2 pairs well with airtight windows, high‑performance insulation, and balanced ventilation controls that together determine whole‑home comfort and air quality.

Product Introduction

For homeowners and small building owners who want balanced, continuous ventilation but do not have room for full ductwork, a ductless HRV like the Lunos e2 offers a compact, wall‑through alternative. Instead of a large central unit and a web of ducts, each e2 module sits in a drilled core hole in an exterior wall, with two units working as a pair to bring in outdoor air and exhaust stale indoor air in a coordinated cycle. On a platform like Rise, this kind of product typically appears alongside airtight window packages, ERVs, and smart ventilation controls, giving designers options for both new high‑performance homes and challenging retrofits where traditional ducted systems are impractical.

What is the Lunos e2 Ductless HRV and How Does It Work?

The Lunos e2 is a small, through‑the‑wall heat recovery ventilator that does not rely on ducts. Each unit consists of an outer weather hood, a cylindrical wall sleeve (tube), a ceramic heat storage core, and a reversible fan. Rather than running one side as supply and another side as exhaust continuously, each fan changes direction on a timed cycle, typically every 60 to 70 seconds. When air flows out, it warms the ceramic core; when the fan reverses, incoming outdoor air passes through the same warm core and picks up much of that stored heat.

Because this regenerative approach only moves air in one direction at a time in each tube, the e2 is installed in synchronized pairs: while one unit exhausts, the other supplies. Over several cycles, the average airflow in and out of the building becomes balanced. This is different from a cross‑flow or counter‑flow HRV core in a ducted system, where supply and exhaust happen simultaneously in separate airstreams, but the end result is similar: outdoor air is pre‑heated (in winter) or pre‑cooled (in summer) by the exhaust air leaving the space.

• Each module is essentially a small, reversible fan with a ceramic heat battery in the wall.
• Units are wired to a controller that keeps paired fans operating 180 degrees out of phase, so total supply and exhaust volumes stay nearly equal.
• Typical residential designs use multiple pairs in different rooms or zones to meet overall ventilation targets.

Key Components of the Lunos e2 System

Understanding the main components helps clarify how the e2 functions, and what installers need to consider. While exact part names may vary by distributor, a typical Lunos e2 installation includes:

• Exterior hood: Provides weather protection, insect screening, and wind protection at the outside wall surface.
• Wall sleeve (tube): A cylindrical, insulated duct that passes through the wall. This defines the length variant (short vs. standard) and must match wall thickness.
• Ceramic regenerative core: A honeycomb or porous ceramic insert that stores and releases heat during each fan reversal cycle.
• Reversible fan module: A small, electronically commutated (EC) fan assembly that can reverse direction and change speed based on the controller setting.
• Interior grille: A trim piece with a filter slot that diffuses airflow and hides the internal components on the room side.
• Controller and wiring: Low‑voltage or line‑voltage controls (depending on version and region) that set fan speed, timing, and synchronization between paired units.

Heat Recovery Efficiency and Regenerative Ceramic Core

A major selling point of the Lunos e2 is its high rated sensible heat recovery efficiency, commonly listed around 85% under standardized test conditions. In practice, this number means that if cold outdoor air at, for example, 14°F (−10°C) enters the core while indoor air is 68°F (20°C), the air leaving the HRV into the room may reach roughly 59–62°F (15–17°C) instead of staying near outdoor temperature. The exact delivered temperature depends on fan speed, cycle timing, wall conditions, and how closely the installation matches laboratory test setups.

The ceramic regenerative core works differently from the plastic or aluminum plates found in many ducted HRVs. During the exhaust phase, warm indoor air transfers heat to the ceramic matrix, raising its temperature. When the fan reverses, the cooler incoming air takes back much of that stored heat. Because the core alternately sees exhaust and supply air, its surface temperature swings around a mean value, and the phase timing is calibrated to give a high average recovery without letting the core cool too far before the next exhaust cycle.

• Published efficiencies are laboratory results; real‑world performance typically trends slightly lower due to wind, wall conditions, and filter loading.
• Efficiency is generally highest at lower airflow rates, where the air spends more time in the core and has more opportunity to transfer heat.
• Because it is a regenerative, not a cross‑flow exchanger, the unit serves one airflow direction at a time, which is why paired units are required.

Partial Humidity Recovery and Indoor Comfort

Although the e2 is normally categorized as an HRV rather than a full ERV (energy recovery ventilator), its ceramic core can provide partial humidity recovery. During the exhaust phase, some moisture in the outgoing air can adsorb into or condense on the ceramic structure. When the direction reverses, a portion of that moisture can re‑evaporate into the incoming airstream. This effect is more pronounced in cold climates where indoor relative humidity is higher than outdoors during winter, and it can slightly reduce the drying effect of ventilation compared with a simple exhaust‑only fan.

However, the degree of humidity transfer should be considered modest. The e2 is not a dehumidifier or dedicated humidity control system. In humid climates or during shoulder seasons, the unit will still bring in outdoor moisture alongside outdoor air, and any latent load must be handled by the building’s heating and cooling system or standalone dehumidifiers. For most low‑energy homes, the e2’s partial humidity recovery is mainly a minor comfort benefit in cold weather rather than a primary design feature.

Airflow Range and Realistic Ventilation Capacity

Each Lunos e2 module has a relatively small fan because it must fit inside a narrow wall sleeve and remain quiet. Manufacturers typically publish airflow rates in the range of roughly 10–20 cubic feet per minute (cfm) per unit, depending on speed setting and test standard. At lower speeds, noise and power draw are minimized; at higher speeds, ventilation capacity increases but with more audible fan noise and slightly lower heat recovery efficiency.

Because the system operates in pairs, the effective balanced airflow per pair usually falls in the range of a modest bathroom fan. For example, two e2 units run at a medium setting might together provide on the order of 20–30 cfm of net continuous ventilation. This is adequate for many tight bedrooms, small apartments, or high‑performance homes where design air change rates are low, but it will not replace large commercial HRVs in buildings with high occupancy or large floor areas.

• Plan on multiple pairs to meet whole‑house ventilation targets based on standards such as ASHRAE 62.2 or local equivalents.
• Sizing should account for both average continuous flow and the fact that each unit’s direction cycles; the balanced flow is averaged over time, not instantaneous.
• For intermittent boost (for example, higher airflow when a bathroom is in use), higher fan settings can be used temporarily, with higher noise levels.

Suitability for Low‑Energy and Passive House‑Style Homes

The e2 was developed in Europe, where very airtight, small to medium‑sized homes are common, and where low continuous ventilation rates can adequately control indoor air quality. In that context, several pairs of e2 units can satisfy whole‑house requirements with minimal ductwork. The system is often used in low‑energy or Passive House‑style buildings where envelope leakage is low and internal heat gains are predictable.

In North American homes, which vary widely in airtightness and layout, designers should verify that total installed e2 capacity aligns with the calculated ventilation needs. In an older or leakier house, these small fans might not be able to offset infiltration and internal pollutants alone. In those cases, e2 units are sometimes combined with other strategies, such as dedicated bath fans or a small ducted HRV serving key areas, to achieve both code compliance and comfort.

Electrical Requirements and Power Consumption

One of the defining features of the Lunos e2 is its ultra‑low electrical consumption. A single fan typically uses only a few watts at low speed and may draw under 5 W even at medium settings. Exact values depend on the specific version and regional configuration, but the order of magnitude is significantly lower than many traditional HRV blowers that serve whole‑house duct systems.

From an electrical perspective, there are two main considerations: supply voltage and control wiring. European versions are commonly supplied for 230 V operation and use local control modules. North American distributors typically provide versions compatible with 120 V, sometimes using plug‑in power supplies or in‑wall transformers, and proprietary controllers for speed selection and synchronization. Electricians and installers should follow the specific wiring diagrams supplied with the product version they are using and must coordinate with local codes for low‑voltage or line‑voltage classification.

• Steady‑state power draw for a pair of e2 units at low speed is often similar to, or less than, the consumption of an LED light bulb.
• Electrical load is usually small enough that adding several units rarely requires panel upgrades, but cumulative loads should still be tallied during design.
• Because controls are specific to the HRV system, it is not typically wired directly to generic smart switches or dimmers; compatibility should be verified.

Noise Levels and Suitability for Living Spaces

Quiet operation is important when ventilation devices are installed directly in bedrooms and living rooms, particularly because ductless HRVs have no long duct runs to attenuate sound. Manufacturers of the Lunos e2 design the fan and housing to keep sound pressure levels relatively low, typically in a range intended to blend with background noise in residential spaces when used at normal continuous speeds.

As with most fans, noise increases with speed. At the lowest or medium settings, many users find the sound level acceptable or barely noticeable, often comparable to a gentle airflow or a small computer fan. At maximum speed (for boost or rapid air change), the fan may be clearly audible, which is why many designs use higher speeds only intermittently. Proper installation – including fully seated sleeves, tight seams, and correct exterior hood placement – also affects actual noise transfer, both from the fan itself and from outdoor sounds passing through the wall opening.

• Noise is typically specified in decibels (dB(A)) at specific speeds and measured in accordance with regional standards; comparing these values with common household sounds can help set expectations.
• Bedrooms often benefit from operating e2 units on the lowest fan setting for overnight use, with higher flows scheduled at other times in shared spaces.
• Acoustic performance can be degraded if the unit is installed in very thin walls without sufficient mass or if gaps remain around the tube.

Short vs. Standard Lunos e2 Variants: Wall Thickness and Tube Length

The primary difference between the short and standard Lunos e2 variants is the length of the wall sleeve (tube) and the associated fan insertion depth. Both variants share the same general operating principle and core design, but they are optimized for different wall assemblies. Selecting the right length is essential to maintain thermal performance, weather resistance, and acoustic isolation.

In general terms, the short version is intended for thinner walls, such as older masonry, lightweight framed walls, or interior partitions that have been converted for ventilation. The standard version is designed for typical modern exterior walls with more insulation depth. Many suppliers also offer extension options or accessories to adapt the tube for extra‑thick walls, such as deep double‑stud assemblies or walls with exterior insulation and rain‑screen cladding.

• Short variant: Shorter tube that can fit walls that are only a few inches thick (for example, some retrofit masonry or panelized structures), while still allowing room for the ceramic core and fan.
• Standard variant: Longer tube suitable for common North American exterior wall thicknesses in the range typical for 2x4 or 2x6 framing plus sheathing and cladding.
• Extra‑long options: Some distributors supply extension sleeves or custom tube lengths for walls with heavy exterior insulation or deep window returns; designers should verify maximum allowable tube length recommended by the manufacturer.

Why Tube Length and Fan Depth Matter

Tube length and fan depth affect more than just whether the unit physically reaches from inside to outside. They also influence thermal bridging, condensation risk, and sound transmission. If the tube is too short relative to the wall, installers may need to improvise with additional insulation or spacers, which can lead to gaps or unwanted air leakage paths. If the tube is too long or not properly aligned, the fan may not seal correctly, and the ceramic core may not sit in the intended position, reducing heat recovery efficiency.

Matching tube length to wall thickness allows the interior grille and exterior hood to sit flush, with the insulated tube spanning the cold‑to‑warm transition through the wall. This helps keep the core in a more stable temperature zone, reduces the chance of condensation at the interior surface during cold weather, and improves acoustic damping. Installers should measure actual wall thickness, including interior finishes and exterior cladding, and compare with the manufacturer’s specified wall thickness ranges for the short and standard models.

Installation Considerations: Core Drilling, Placement, and Weather Protection

Installing a Lunos e2 typically involves core‑drilling a round hole through the exterior wall, inserting the insulated tube, and then placing the ceramic core and fan module. Because the hole passes completely through the envelope, attention to air sealing and water management is critical. Many installers prefer to drill with a slight slope to the exterior to encourage any incidental water to drain outwards rather than inwards.

Placement is also important. For paired operation, units are often installed in opposite walls of the same room or in adjacent rooms, depending on the ventilation strategy. Locating units near exterior noise sources, such as busy roads, can increase sound intrusion, while placing them near building corners may expose exterior hoods to wind effects that alter airflow. Coordinating locations with interior furnishings helps ensure that incoming airstreams do not blow directly on occupants, and that filters are accessible for maintenance.

• Core drilling usually requires specialized tools, especially in concrete or brick; professional installation is common, particularly in multi‑family or engineered structures.
• Penetrations should be integrated into the wall’s weather‑resistive barrier and air barrier systems, with appropriate flashing and sealants.
• Local codes may require specific clearances for exterior hoods relative to property lines, windows, or combustion appliance vents.

Retrofits vs. New Construction

In retrofit applications, the e2’s ductless design is a major advantage because it avoids tearing into ceilings and walls to run ducts. Units can be installed in individual rooms that lack fresh air, provided there is an appropriate exterior wall location and no conflicts with existing structural elements or utilities. However, drilling through older masonry or unknown wall assemblies can uncover surprises, so pre‑installation scanning or inspection may be necessary.

In new construction, designers can plan for e2 locations at the framing stage, ensuring that structural members leave space for the required core holes and that the wall assembly around the tube is detailed for air sealing and insulation continuity. This is also the best time to coordinate electrical circuits and control wiring so that wall switches and controllers are logically located. For high‑performance homes, early planning can prevent conflicts between e2 placements and other penetrations such as windows, dryer vents, and heat‑pump line sets.

Balanced Ventilation Without Ductwork: How Pairs Synchronize

A common question is how the e2 can be considered a balanced ventilation system when each unit alternately exhausts and supplies air. The answer lies in synchronized operation. Controllers pair two units so that when one is in exhaust mode, the other is in supply mode. After a set interval, they reverse simultaneously. Over time, the total volume of air exhausted by the first unit equals the total volume supplied by the second (and vice versa), so the net airflow across the building envelope is approximately balanced.

While there may be slight imbalances during any given instant or cycle, especially if wind or stack effects influence one unit more than the other, the long‑term average ventilation is close to balanced, which helps maintain indoor pressure near neutral. This is particularly important in airtight, low‑energy homes where continuous negative or positive pressure can drive unwanted infiltration through small leaks and affect combustion appliance venting. For buildings that require very precise pressurization control, designers should review whether a regenerative, cyclical system like the e2 is appropriate for all zones.

• Balanced does not mean perfectly identical at every second; it refers to the average supply and exhaust volumes over time.
• Controllers typically allow multiple pairs to be grouped so that the house behaves as a coordinated system rather than disconnected individual fans.
• Door undercuts and interior transfer grilles may still be needed to let air move between rooms and avoid stagnation.

Compliance with European Building and Ventilation Standards

The Lunos e2 is developed and manufactured in Europe, where ventilation systems are commonly tested and certified under standards such as EN 13141 (performance testing for residential ventilation components) and subject to national building regulations that specify minimum airflow rates, efficiency, and acoustics. Test results under these standards form the basis for manufacturer claims regarding heat recovery efficiency, airflow, and sound levels.

For low‑energy and Passive House‑style homes, many designers look for components that have been evaluated by organizations such as the Passive House Institute (PHI) or similar bodies. Some Lunos products have been used in projects aiming to meet these voluntary standards, in part because the combination of high rated efficiency and low electrical consumption can contribute to overall energy targets. However, achieving whole‑building certification depends on how the entire ventilation system is designed and operated, not on the HRV alone.

When the e2 is imported or distributed in North America, it must also fit within local code frameworks, which may refer to ASHRAE, CSA, or other national standards. Building officials may request documentation of airflow, efficiency, and noise levels, especially in multi‑family or commercial applications. Designers should confirm that the version they are specifying carries any required labels or approvals for their jurisdiction.

Ideal Use Cases for the Lunos e2 Ductless HRV

Because the e2 has modest airflow per unit, high heat recovery efficiency, and very low energy consumption, it is particularly well‑suited to specific building types and scenarios. When used within its performance envelope, it can provide reliable, low‑maintenance ventilation without large mechanical rooms or duct chases. When pushed beyond that envelope, it may struggle to keep up with pollutant loads or humidity, especially in large or leaky buildings.

The following scenarios often align well with a ductless HRV system like the Lunos e2:

• Small, airtight homes and apartments: Units with low design ventilation loads where a few paired modules can meet continuous airflow requirements.
• Deep energy retrofits: Older homes undergoing envelope upgrades where adding full ductwork would be expensive or disruptive.
• Room‑by‑room ventilation: Situations where individual rooms (such as bedrooms or home offices) require dedicated fresh air independent of central ducted systems.
• Multi‑unit buildings: Apartments or condos where each unit can have its own ductless HRV pair, simplifying metering and occupant control compared with centralized systems.
• Light‑commercial spaces: Small offices or studios with relatively low occupant density and exterior walls suitable for through‑wall units, provided local codes allow such solutions.

Situations Where a Ducted HRV/ERV May Be Preferable

In larger buildings or homes with complex layouts, a centralized ducted HRV or ERV may still be more appropriate. Ducted systems can supply and exhaust air from many rooms simultaneously and can deliver higher airflow rates, which may be necessary to meet ventilation standards in high‑occupancy spaces or in buildings with significant internal pollutant sources.

If a building already has a well‑designed duct network for heating and cooling, adding a ducted HRV or ERV can leverage those ducts for more uniform air distribution. Additionally, some advanced systems integrate with smart controls, humidity sensors, and demand‑controlled strategies at the whole‑building level. In such cases, the added complexity of a ductless, pair‑based system might not offer clear advantages.

Maintenance Requirements and Filter Management

Like any HRV, the Lunos e2 requires regular maintenance to sustain performance. The most common tasks are cleaning or replacing filters and occasionally inspecting the ceramic core and fan for dust buildup. Filters are typically accessible from the interior side behind the grille, and maintenance can usually be performed with basic tools or none at all.

In dusty environments or homes with pets, filters may load more quickly, reducing airflow and slightly increasing fan noise as the fan works against higher resistance. Manufacturers typically recommend inspection intervals on the order of several months, but actual schedules depend on local conditions. The ceramic core can often be removed and washed according to the manufacturer’s instructions if performance declines due to heavy accumulation of particulates.

• Homeowners should be comfortable removing the interior grille and handling filters; simple instructions and reminders can improve long‑term performance.
• If users neglect maintenance, effective airflow can drop, even though fan power consumption remains low.
• In rental or multi‑family situations, property managers may want to standardize maintenance intervals and stocking of replacement filters.

Integration with Other High‑Performance Home Systems

Ventilation does not operate in isolation. The overall comfort and energy performance of a home depend on how air exchange, insulation, airtightness, and heating and cooling systems work together. In low‑energy homes equipped with products like high‑performance windows, advanced insulation, and efficient heat pumps, a small, efficient HRV such as the Lunos e2 can help match ventilation energy use to the reduced heating and cooling demand.

On an e‑commerce site focusing on sustainable building products, a Lunos e2 product page often sits alongside ERVs, smart thermostats, and air quality monitors. When designers or homeowners select a ductless HRV, they should also consider whether the building requires additional exhaust fans, how they will monitor indoor CO₂ and humidity, and whether local rebates or incentives exist for high‑efficiency ventilation systems.

Comparing Lunos e2 with Other Ductless HRV/ERV Options

The Lunos e2 is one of several ductless HRV or ERV units on the market. Many of these products share a common concept: through‑wall installation, regenerative or small plate heat exchangers, and paired or synchronized operation for balanced airflow. Differences appear in details such as heat recovery efficiency, maximum airflow, sound levels, filter class, and control options.

When comparing systems, technical buyers often look at metrics such as efficiency at different airflows, power consumption per cfm (or per cubic meter per hour), and sound levels at standardized distances. They may also consider whether the system supports humidity transfer (ERV behavior), whether it has frost‑protection functions for cold climates, and how easily it integrates with third‑party controls or building automation systems. In this context, the e2’s strengths tend to be its high efficiency rating, very low power draw, and compact form factor, while its limitations are the modest maximum airflow per unit and the need for multiple wall penetrations in larger buildings.

Real‑World Performance: What Homeowners Can Expect

In day‑to‑day use, a properly designed Lunos e2 system should provide a steady supply of tempered outdoor air, with room temperatures remaining close to those maintained by the main heating or cooling system. In winter, incoming air should feel noticeably warmer than outdoor air when it exits the interior grille, though it may still be cooler than room air. In summer, particularly in dry climates or during cooler nights, the system can help remove indoor heat by pre‑cooling incoming air with outgoing indoor air.

For indoor air quality, continuous operation helps dilute CO₂, odors, and pollutants from cooking, cleaning products, and off‑gassing materials. However, because each unit serves a specific location, air mixing across rooms depends on interior doors and transfer paths. For example, if bedroom doors are kept closed, those rooms benefit most from having their own dedicated e2 units rather than relying solely on a central unit located elsewhere. Occupants should also be aware that the system does not provide active filtration for very fine particulates unless fitted with higher‑efficiency filters approved by the manufacturer, and it does not neutralize outdoor pollutants such as wildfire smoke or traffic emissions without added filtration.

Key Design and Specification Checklist

For designers, installers, or informed homeowners specifying a Lunos e2 system, the following checklist can help ensure that the system aligns with project goals and constraints:

• Confirm total ventilation requirement based on occupancy, floor area, and applicable standards (such as ASHRAE 62.2, local codes, or European guidelines).
• Determine how many e2 pairs are required to meet that total at the planned operating speed, leaving some margin for boost mode when needed.
• Measure actual wall thicknesses (including finishes and claddings) to decide between short and standard variants and any needed extension accessories.
• Plan core hole locations to avoid structural members, electrical wiring, plumbing, and other penetrations, and to respect exterior clearance requirements.
• Coordinate electrical supply and control wiring routes and ensure compatibility with the product version’s voltage and controller requirements.
• Detail air sealing and flashing around the wall sleeve to protect the building envelope and minimize uncontrolled leakage.
• Establish a maintenance plan for filter cleaning and replacement, including homeowner instructions or building management procedures.

Conclusion: Where the Lunos e2 Fits in Modern Ventilation Strategies

The Lunos e2 ductless HRV system occupies a specific niche in the ventilation landscape. It offers continuous, balanced ventilation through exterior walls, with high rated heat recovery efficiency, partial humidity recovery, and very low electrical consumption. Its regenerative ceramic core and reversible fan design make it compact enough to live in bedrooms and living areas, and its sound levels at normal speeds are intended to be compatible with these spaces.

Choosing between the short and standard variants mainly comes down to matching tube length to wall thickness, ensuring that thermal performance, acoustics, and weather protection are preserved. Designers and homeowners considering the e2 should weigh its advantages – ductless installation, energy efficiency, and scalability through multiple pairs – against its limitations in airflow capacity and the need for careful planning of wall penetrations. When applied in the right context, particularly in low‑energy homes or challenging retrofits, the Lunos e2 can be a technically sound solution for balanced, continuous ventilation without conventional ductwork.

Sources

• Lunos — Product documentation and technical data for Lunos e2 decentralized heat recovery ventilator https://www.lunos.de
• Passive House Institute — Component criteria and guidance for ventilation units in low‑energy buildings https://passiv.de
• European Committee for Standardization (CEN) — EN 13141 series on performance testing of residential ventilation components https://www.cen.eu
• ASHRAE — ANSI/ASHRAE Standard 62.2: Ventilation and Acceptable Indoor Air Quality in Residential Buildings https://www.ashrae.org
• U.S. Department of Energy — Guides and resources on energy‑efficient ventilation strategies for homes https://www.energy.gov