Balanced Ventilation After Air Sealing: An HRV and ERV Field Guide

Air sealing reduces uncontrolled leakage, but it also changes how a building receives outdoor air and removes moisture and pollutants. After a meaningful enclosure upgrade, “the house used to breathe” is not a ventilation strategy. The safer approach is to measure the new enclosure, identify pollutant sources, calculate the required airflow, and commission a mechanical system that delivers it.

The U.S. Department of Energy’s Building Science Education guidance explains that whole-house ventilation uses fans and ducts to exhaust stale air, supply outdoor air, or do both. It also distinguishes whole-house ventilation from intermittent kitchen and bathroom exhaust. Both are important, but they solve different problems.

Begin with the building, not the equipment catalog

Before choosing an HRV or ERV, document what changed and what remains. Review the air-sealing scope, insulation work, new windows, HVAC replacements, combustion appliances, attached garages, crawlspaces, and known moisture problems. If a blower-door test was performed, retain both pre- and post-work results. Our blower-door testing guide explains how CFM50 and ACH50 support an air-sealing plan.

A tighter enclosure or one air-leakage number does not determine the final airflow. Occupancy, floor area, bedrooms, existing exhaust, and the applicable standard also matter.

The assessment should answer:

• Which rooms produce moisture, odors, particles, or combustion byproducts?
• Are kitchen and bathroom fans ducted outdoors and actually moving air?
• Are there atmospheric-combustion appliances that need safety testing?
• Where can outdoor air be drawn in without collecting vehicle exhaust, dryer exhaust, or other contaminants?
• Can supply air reach bedrooms and living areas when doors are closed?
• Is there a practical path for dedicated ventilation ducts, drains, controls, and service access?

Ventilation can help manage normal indoor moisture; it cannot repair a wet foundation, roof, or plumbing leak.

Understand the four basic system approaches

DOE describes exhaust-only, supply-only, balanced, and energy-recovery strategies. Each creates a different pressure relationship.

An exhaust-only system removes indoor air and relies on intentional inlets or enclosure leakage for replacement air. It can be comparatively simple, but it may pull air through garages, crawlspaces, attics, or other undesirable paths if the pressure plan is poor.

A supply-only system delivers outdoor air and lets indoor air leave through leakage and exhaust paths. It can support filtration and distribution, but it may push moist indoor air into assemblies during cold weather or introduce humid outdoor air during cooling season if it is not integrated carefully.

A balanced system supplies and exhausts approximately equal airflows. It offers greater control over where air enters and leaves. Heat recovery ventilators and energy recovery ventilators are balanced systems with an air-to-air core that reduces the energy penalty of ventilation.

An HRV transfers sensible heat between outgoing and incoming airstreams. An ERV transfers sensible heat and a portion of the moisture. Neither device is a furnace, air conditioner, dehumidifier, air purifier, or substitute for source control.

Choose HRV versus ERV from loads and climate

There is no universal HRV-versus-ERV rule. The decision should consider winter temperature, summer humidity, indoor humidity targets, occupancy density, air-conditioning and dehumidification capacity, frost-control strategy, and the moisture sensitivity of the enclosure.

An HRV may be useful where removing indoor moisture during a long heating season is a priority. An ERV may reduce the amount of outdoor moisture introduced during humid weather and can help retain some indoor moisture in winter. However, an ERV does not block all moisture, and a moisture-transfer core cannot correct an undersized cooling system, poor drainage, wet basement, or excessive internal moisture generation.

Ask the designer to document the assumed outdoor and indoor conditions, sensible and latent loads, recovery ratings used in the calculation, and expected supply-air condition at representative winter and summer design points.

Size to the governing standard—and verify adoption

ANSI/ASHRAE Standard 62.2 addresses dwelling-unit ventilation, local mechanical exhaust, and source control. ASHRAE’s current page identifies Standard 62.2-2025 as the residential ventilation and indoor-air-quality standard and notes that the 2025 edition includes updated filtration and local-exhaust provisions.

Do not assume the newest edition is the legally adopted edition. DOE’s Building Energy Codes Program explains that codes are adopted at state and local levels and implemented locally. The project team should confirm the adopted building, mechanical, energy, fire, and fuel-gas codes with the authority having jurisdiction.

For an existing home, measure the installed system rather than accepting the equipment label. Fan airflow changes with duct length, fittings, grilles, filters, core condition, and external static pressure. Select a unit with enough capacity at the expected resistance, but avoid using excessive airflow as a substitute for design.

Design the air pathways

A good box connected to poor ducts is a poor ventilation system. Keep ducts short and smooth where possible, seal joints, insulate runs through unconditioned areas, and provide accessible filter and core service. Follow the manufacturer’s requirements for condensate drainage and frost protection.

Locate the outdoor-air intake away from contamination sources and where snow, leaves, pests, and wind-driven rain can be managed. Separate intake and exhaust terminations as required by the adopted code and manufacturer. Do not discharge ventilation air into an attic, crawlspace, garage, or wall cavity.

Distribution also matters. Whole-house outdoor air should reach occupied rooms, while stale air is commonly collected near bathrooms, laundry areas, or other appropriate locations. Transfer grilles, door undercuts, or dedicated returns may be needed so closed bedrooms are not isolated from the airflow path.

Choose filters based on the unit’s approved resistance and the project requirement. ASHRAE reports that the 2025 edition of Standard 62.2 changed its referenced filtration level from MERV 6 to MERV 11, but the applicable project requirements still depend on the adopted standard and system design. A higher-efficiency filter that causes excessive pressure drop can reduce delivered ventilation.

Keep source control and local exhaust

Whole-house ventilation does not eliminate the need for direct kitchen and bathroom exhaust. Capture cooking pollutants near the source and discharge them outdoors. Bathroom fans should remove moisture where it is generated. Clothes dryers, central vacuums, fireplaces, and large range hoods also affect pressure and must be considered in testing.

EPA’s current Indoor AirPlus program documents provide verification requirements and checklists for homes and apartments. Even when a project is not pursuing certification, the documents are useful reminders that indoor-air-quality work involves design, installation, verification, and occupant information—not just equipment selection. Do not describe a project as Indoor AirPlus certified unless it completes the program’s required certification process.

Commission under realistic conditions

Commissioning should occur after final filters, grilles, doors, and controls are installed. At minimum:

• Measure supply and exhaust airflow using appropriate instruments.
• Balance the two airstreams to the design targets.
• Record external static pressure and operating speed.
• Confirm intake and exhaust locations and airflow direction.
• Test boost, timer, manual override, defrost, and interlock functions.
• Verify condensate drainage and cold-weather protection.
• Check sound and vibration at normal and boost settings.
• Operate major exhaust appliances and complete required combustion-safety testing.
• Label controls, filters, ducts, and service panels.
• Give occupants a plain-language operating and maintenance guide.

A commissioning report should state the design airflow, measured airflow at each terminal, total supply and exhaust, control settings, filter specification, and corrective actions.

Plan for operation, maintenance, and funding

Assign responsibility for cleaning exterior hoods, replacing filters, cleaning the core, checking drains, and repeating airflow measurements. Maintenance intervals should follow the manufacturer and site conditions; wildfire smoke, construction dust, pets, and nearby traffic may justify more frequent inspection. Occupants should know when to use boost mode and when an outdoor-air event may require temporary shutdown under the manufacturer’s guidance.

For 2026 budgeting, do not assume a federal Energy Efficient Home Improvement Credit. The IRS termination guidance states that Section 25C is not allowed for property placed in service after December 31, 2025. State, local, or utility programs may still support ventilation or comprehensive retrofit work, but obtain written eligibility and preapproval from the administering program before purchasing equipment.

The best ventilation project connects enclosure testing, equipment selection, measured airflow, controls, and maintenance in one record. BPMS can help building-performance teams organize audit evidence and reporting, while qualified designers, installers, and code officials remain responsible for the system design and approvals.