How to Choose an ERV/HRV for a 100–200 m² House

Choosing an energy recovery ventilator or heat recovery ventilator is not simply a matter of matching a product to the floor area of a house.

Two houses of the same size may require different ventilation capacities because of differences in ceiling height, occupancy, room layout, duct length, climate and indoor air quality requirements.

For residential projects between 100 and 200 m², the correct selection process should consider not only the rated airflow of the unit but also its real operating airflow after installation.

This guide explains how homeowners, HVAC contractors and distributors can make a preliminary ERV or HRV selection for a residential project.

What Is an ERV or HRV?

An HRV, or heat recovery ventilator, brings outdoor air into a building while exhausting stale indoor air. Inside the heat exchanger, heat is transferred between the two air streams without directly mixing them.

An ERV, or energy recovery ventilator, works in a similar way but can transfer both sensible heat and part of the moisture energy.

In winter, the outgoing warm indoor air helps preheat the incoming cold air. In summer, the outgoing cooler air helps reduce the temperature and energy load of the incoming outdoor air.

Compared with opening windows or using exhaust fans alone, a balanced ERV or HRV system can provide more controlled ventilation while reducing unnecessary heating and cooling losses.

The choice between an ERV and an HRV normally depends on:

• Local outdoor temperature and humidity
• Indoor humidity requirements
• Building airtightness
• Heating and cooling system
• Applicable building and ventilation standards

An ERV can be particularly useful in humid, mixed or comfort-focused climates. An HRV is often considered for cold and relatively dry climates. However, the final decision should always be based on the actual building conditions.

Why Floor Area Alone Is Not Enough

Product selection charts often recommend a certain airflow according to floor area. These charts are useful for initial screening, but they should not replace a ventilation calculation.

A 150 m² house occupied by two people does not have the same ventilation demand as a 150 m² house occupied by six people.

The following factors can change the required airflow:

• Number of permanent occupants
• Ceiling height
• Number of bedrooms and bathrooms
• Building airtightness
• Indoor pollutant sources
• Local climate
• Duct length and number of bends
• Filter resistance
• Required operating noise
• Local ventilation regulations

Method 1: Calculate Airflow by Room Volume

One common method is to calculate the required airflow using the internal volume of the house and the target air change rate.

For example, consider a 100 m² house with a ceiling height of 2.7 metres and a target air change rate of 0.5 ACH:

100 × 2.7 × 0.5 = 135 m³/h

The preliminary ventilation demand is therefore 135 m³/h.

If the target air change rate is increased to 0.7 ACH:

100 × 2.7 × 0.7 = 189 m³/h

This demonstrates why it is not accurate to select a ventilator from floor area alone. The required airflow changes considerably when the target air change rate changes.

The appropriate air change rate should be determined according to local regulations, occupancy and indoor air quality requirements.

Method 2: Calculate Airflow by Occupancy

A second method is to calculate the required outdoor airflow according to the number of occupants.

If a project uses a preliminary value of 30 m³/h per person, a house with four permanent occupants would require:

4 × 30 = 120 m³/h

A house with six occupants would require:

6 × 30 = 180 m³/h

The exact airflow requirement per person varies between countries and ventilation standards. Local codes and project specifications should always take priority.

Compare the Two Results

After calculating airflow by volume and by occupancy, compare the two results. The higher value can be used as the preliminary design airflow.

For a 100 m² house with four occupants:

• Airflow by volume: 135 m³/h
• Airflow by occupancy: 120 m³/h
• Preliminary design airflow: 135 m³/h

This value does not necessarily mean that a ventilator rated at exactly 135 m³/h should be selected. The airflow available after connecting the duct system may be lower than the airflow shown under ideal test conditions.

A suitable unit should be selected after checking the fan performance, external static pressure and intended operating speed.

Preliminary Airflow Examples for 100–200 m² Houses

The following table provides simplified examples for initial product screening.

These calculations are examples, not universal model recommendations.

A residential project may require a higher-capacity unit when it has:

• Long duct runs
• Several branches and bends
• High-efficiency filters
• Multiple bathrooms
• High occupancy
• Higher target air change rates
• Strict indoor air quality requirements

The final unit should also be able to provide the required airflow without continuously operating at its maximum speed.

Check External Static Pressure

Rated airflow is only one part of ERV or HRV selection.

Once the unit is connected to ducts, filters, silencers, grilles, valves and distribution boxes, the airflow meets resistance. This resistance is expressed as external static pressure.

A ventilator may provide its advertised maximum airflow under low-resistance conditions but deliver considerably less airflow after being connected to a complex duct network.

HVAC designers and installers should consider pressure losses from:

• Supply and exhaust ducts
• Duct length and diameter
• Elbows and fittings
• Air distribution boxes
• Supply and extract valves
• Outdoor intake and exhaust grilles
• Filters
• Silencers
• Fire or balancing dampers

Do Not Design the System Around Maximum Speed

Selecting an undersized unit and operating it at maximum speed every day can create several problems:

• Higher operating noise
• Greater fan energy consumption
• Faster filter loading
• Reduced adjustment range
• Less capacity for temporary high-demand ventilation
• Possible occupant complaints

A better approach is to select a unit that can deliver the normal design airflow at a medium or suitable operating speed.

Higher speed can then be reserved for temporary conditions such as:

• Increased occupancy
• Parties and gatherings
• Higher indoor CO₂ levels
• Bathroom use
• Rapid removal of odours
• Short-term ventilation demand

However, excessive oversizing should also be avoided. A unit that is much larger than required may increase installation cost, duct noise and energy consumption.

Consider Air Distribution, Not Only Total Airflow

Even if the total airflow is sufficient, the ventilation system may still perform poorly if the air is not distributed correctly.

Fresh air is normally supplied to:

• Bedrooms
• Living rooms
• Home offices

Stale air is normally extracted from:

• Bathrooms
• Toilets
• Utility rooms
• Other humid or polluted zones

Air must be able to move from supply rooms toward extract rooms. Door undercuts, transfer grilles or other transfer paths may therefore be required.

Kitchens with cooking grease usually require a separate range hood or dedicated exhaust system. The kitchen hood should not automatically be connected to the heat-recovery ventilation duct because grease can contaminate the ductwork, filters and heat exchanger.

Each room should receive an appropriate portion of the total airflow. After installation, the air terminals should be measured and balanced rather than adjusted only by visual judgement.

Noise Is Affected by Both the Unit and Installation

Ventilation noise does not come only from the ERV or HRV itself.

The final sound level can also be affected by:

• Excessive air velocity
• Small duct diameter
• Sharp duct bends
• Poorly selected air valves
• Lack of silencers
• Rigid mounting without vibration isolation
• Installation directly above a bedroom
• Continuous maximum-speed operation

For quieter residential operation, the main unit should preferably be installed in a service area, corridor ceiling, utility room or another maintainable location away from noise-sensitive rooms.

The system may also require:

• Vibration isolation
• Flexible connectors
• Acoustic ducting or silencers
• Properly sized main ducts
• Lower air velocity near bedrooms
• Correct commissioning and balancing

Evaluate the Filtration System

Filtration is especially important in regions affected by dust, pollen, PM2.5 or other outdoor particles.

When evaluating an ERV or HRV, consider:

• Filter grade
• Filter arrangement
• Replacement availability
• Filter access
• Maintenance frequency
• Pressure drop when the filter becomes dirty
• Availability of replacement filters in the local market

Higher-efficiency filters can improve particle removal, but they also create additional airflow resistance. The fan and duct system must be capable of maintaining the required airflow as the filter resistance increases.

Check Heat-Recovery Performance Carefully

Heat-recovery performance can help reduce the load created by outdoor ventilation air. However, buyers should check how the efficiency value was measured.

Important questions include:

• Is it temperature efficiency or enthalpy efficiency?
• At which airflow was it tested?
• What were the indoor and outdoor test conditions?
• Does the efficiency decrease at higher airflow?
• Is the heat exchanger suitable for the local climate?
• Is frost protection required?
• Does the unit include a bypass function?

A bypass mode can be useful during mild outdoor conditions. When the outdoor air is suitable for free cooling or direct ventilation, the air can bypass the heat exchanger rather than recovering unwanted heat.

In cold regions, frost protection and condensate management may also be important parts of the system design.

Think About Maintenance Before Installation

Filters and heat exchangers require inspection and maintenance. A technically good unit can become difficult to operate if it is installed without enough service space.

Before installation, confirm:

• Filter removal direction
• Access panel position
• Required ceiling opening
• Condensate drainage
• Heat-exchanger cleaning method
• Availability of replacement filters
• Access to electrical and control components
• Recommended maintenance intervals

The installer should not place the unit in a permanently sealed ceiling or an area that cannot be reached safely.

MENRED Residential Energy Recovery Ventilation

MENRED provides energy recovery ventilation, heat recovery ventilation and indoor climate control solutions for residential and commercial applications.

For whole-house residential ventilation, MENRED systems can combine:

• Balanced fresh-air supply and stale-air exhaust
• Energy or heat recovery
• Multi-stage air filtration
• DC fan technology
• Smart controllers
• App-based management on selected models
• RS485 communication on selected systems
• Seasonal bypass operation on selected models
• Air quality monitoring and system integration options

For example, selected MENRED residential energy recovery ventilators provide rated airflow around 350 m³/h. This airflow range may be considered for certain medium-sized houses, but suitability must still be verified using occupancy, building volume, duct resistance and room-by-room airflow calculations.

MENRED can assist distributors, HVAC contractors and project partners with preliminary product selection based on the project information provided.

Information Required for ERV/HRV Selection

To recommend a suitable ventilation unit, the following information should be collected:

1. Country and project location
2. Total ventilated floor area
3. Ceiling height
4. Number of floors
5. Number of permanent occupants
6. Number of bedrooms and bathrooms
7. Floor plan
8. Approximate duct length
9. Preferred installation location
10. Local winter and summer conditions
11. Required filter grade
12. Power supply
13. Control and communication requirements
14. Applicable certification or building-code requirements

Providing only the floor area is enough for an initial discussion, but it is not enough for final equipment selection.

Common ERV/HRV Selection Mistakes

Selecting Only by Floor Area

Floor area does not account for occupancy, ceiling height, duct resistance or room layout.

Choosing the Maximum Airflow as the Design Airflow

The actual airflow after installation may be lower because of duct and filter resistance.

Assuming Bigger Is Always Better

Oversizing can increase noise, power consumption and installation cost.

Ignoring the Duct System

Even a high-performance ventilator cannot compensate for badly sized or poorly installed ducts.

Ignoring Filter Maintenance

Dirty filters increase pressure loss and reduce ventilation airflow.

Using One Airflow Value for Every Room

Bedrooms, living rooms and extract areas have different ventilation requirements.

Confusing Ventilation with Air Conditioning

An ERV or HRV provides controlled ventilation and energy recovery. It does not automatically replace the heating, cooling or dehumidification system.

Frequently Asked Questions

What size ERV do I need for a 100 m² house?

For a 100 m² house with a 2.7 m ceiling, a preliminary calculation at 0.5 ACH gives 135 m³/h. Occupancy and duct resistance must also be checked before selecting the unit.

What size ERV do I need for a 150 m² house?

At a ceiling height of 2.7 m and 0.5 ACH, the preliminary airflow is approximately 203 m³/h. Depending on occupancy and system resistance, a higher nominal unit capacity may be required.

Is a 350 m³/h ERV suitable for a 200 m² house?

It may be suitable for some 200 m² residential projects. However, the required airflow, fan performance at the calculated static pressure, room distribution and operating noise must be verified.

Should the ERV run continuously?

Whole-house ventilation systems are generally designed to provide continuous or scheduled background ventilation, with higher airflow used when required. The actual operating strategy should follow the project design and local requirements.

Can an ERV control indoor humidity?

An ERV can transfer part of the moisture energy between incoming and outgoing air, helping reduce the ventilation-related humidity load. It is not necessarily a substitute for a dedicated dehumidifier or humidifier.

Can I choose an ERV without a floor plan?

A preliminary airflow range can be estimated from the floor area, ceiling height and occupancy. A floor plan is normally required for room-by-room airflow distribution and duct design.

Conclusion

Selecting an ERV or HRV for a 100–200 m² house requires more than checking an area chart.

A reliable selection process should include:

• Airflow calculation by building volume
• Airflow calculation by occupancy
• Room-by-room air distribution
• Duct resistance and external static pressure
• Noise requirements
• Filtration
• Heat-recovery performance
• Climate conditions
• Maintenance access
• Local standards

Floor area can help identify an initial product range, but final selection should be based on the complete ventilation design.