Buying a Home With an Energy Recovery Ventilator? What Should Be Checked During an Inspection (2026)

What is an ERV and what should buyers check? An Energy Recovery Ventilator (ERV) is a mechanical ventilation device that brings fresh outdoor air into the home while simultaneously exhausting stale indoor air, and transfers heat and moisture between the two air streams to reduce energy loss. Buyers should check that the unit operates (both supply and exhaust fans run), the filters are present and not clogged, the heat exchange core is clean and undamaged, the condensate drain is clear, the ductwork is connected and sealed, and the controls are functioning.

If you're buying a newer or high-performance home in San Diego that has an ERV installed, you're looking at a ventilation system that's more sophisticated (and more maintenance-dependent) than a standard exhaust fan. ERVs are becoming more common in tightly sealed new construction where ASHRAE 62.2 ventilation requirements demand continuous fresh air exchange without the energy penalty of dumping conditioned air outside and pulling in unconditioned air to replace it.

When an ERV works properly, it provides continuous fresh air, controls indoor humidity, and reduces the energy cost of ventilation. When it's neglected, it becomes a clogged, underperforming box that restricts airflow and defeats the purpose of the ventilation system.

How an ERV Works

An ERV has two fans and a heat exchange core.

The exhaust fan pulls stale indoor air from the home (typically from bathrooms, laundry, and other moisture-generating areas) and exhausts it to the outside.

The supply fan pulls fresh outdoor air from an intake vent and delivers it to the home's living spaces (typically through the HVAC ductwork or dedicated supply ducts).

The heat exchange core is where the two air streams pass each other through a series of thin membranes or plates. The outgoing stale air transfers its heat (in winter) or coolness (in summer) to the incoming fresh air. ERV cores also transfer moisture between the air streams, which helps manage indoor humidity. In San Diego's climate, this moisture transfer is beneficial because it prevents the incoming outdoor air from adding excessive humidity during the warm months.

The two air streams never mix directly. They pass on opposite sides of the core membranes, exchanging energy without exchanging air. This is what makes an ERV different from simply opening a window: you get fresh air without losing the energy you've already spent conditioning the indoor air.

What We Check During the Inspection

Unit Operation

We test both fans (supply and exhaust) by activating the ERV at the control and verifying that both air streams are moving. An ERV that runs on only one side (supply without exhaust, or exhaust without supply) is not providing balanced ventilation and may be depressurizing or pressurizing the home.

We check for smooth fan operation, appropriate noise level (excessive noise suggests a failing motor, unbalanced fan, or duct obstruction), and perceptible airflow at both the supply registers and the exhaust grilles.

Filters

ERVs have filters on both the supply and exhaust sides. These filters protect the heat exchange core from dust and debris. We check for filter presence (some homeowners remove filters and never replace them), filter condition (clogged filters restrict airflow and reduce ventilation effectiveness), and correct filter type and size (per manufacturer specifications).

Filters should be replaced every 3 to 6 months depending on the environment. A clogged filter is the most common maintenance failure we find on ERV systems.

Heat Exchange Core

The core is the heart of the ERV. We check for visible dirt or debris buildup on the core surfaces (most cores are accessible through an access panel), physical damage (cracked or broken plates), moisture or condensation inside the unit (normal in small amounts, problematic if excessive), and proper core orientation (some cores are directional and must be installed in the correct position).

A dirty core reduces the energy recovery efficiency and restricts airflow. Most manufacturers recommend cleaning the core annually by rinsing it with water and allowing it to dry completely before reinstalling.

Condensate Drainage

During operation, moisture can condense inside the ERV unit, particularly when there's a significant temperature difference between the indoor and outdoor air streams. The unit has a condensate drain that must be connected to a drain line and kept clear.

A clogged condensate drain causes water to back up inside the unit, which can damage the core, corrode the housing, and create mold conditions inside the ERV itself.

Ductwork

We check the supply and exhaust ductwork for proper connections (no disconnected sections), adequate insulation (to prevent condensation on cold ducts), correct routing (supply duct delivering to living spaces, exhaust duct drawing from wet rooms), and exterior termination of both intake and exhaust vents with proper screens and backdraft dampers.

The intake vent must be separated from the exhaust vent by the manufacturer's recommended distance (typically 6 to 10 feet minimum) to prevent the system from re-ingesting its own exhaust.

Controls

ERV controls range from simple on/off switches to programmable controllers with speed settings, boost modes, and humidity sensors. We check that the control is accessible, functional, and set to a ventilation rate appropriate for the home's size. Many ERVs also integrate with the HVAC system's controls, and the integration logic should be verified (does the ERV run when the HVAC fan runs? Does it operate independently on its own timer?).

Common ERV Defects

Defect	How Common	Impact
Clogged filters	Very common	Reduced airflow, increased energy use, core contamination
Dirty heat exchange core	Common (neglected maintenance)	Reduced energy recovery, restricted airflow
Condensate drain clogged	Moderate	Water backup, mold inside the unit, core damage
One fan not operating	Moderate	Unbalanced ventilation, home pressurization or depressurization
Ductwork disconnected in attic	Moderate	Fresh air not reaching the home, stale air not exhausting
Intake vent too close to exhaust vent	Moderate (installation defect)	System re-ingests its own exhaust
Control set to "off" or lowest setting	Common	Ventilation not meeting ASHRAE 62.2 requirements
Core installed backwards	Occasional (installation defect)	Reduced efficiency, potential moisture problems

ERV Maintenance: What the New Owner Should Know

Maintenance Task	Frequency	Why It Matters
Replace filters	Every 3 to 6 months	Protects the core, maintains airflow
Clean the core	Annually	Maintains energy recovery efficiency
Clear the condensate drain	Annually	Prevents water backup and mold
Check exterior intake and exhaust vents	Annually	Ensure screens are clear, dampers operate
Test both fans	Annually	Verify balanced operation
Check duct connections in attic	Every 2 to 3 years	Ducts can loosen or disconnect over time

If the seller has the ERV's maintenance records, request them. If not, plan to have the system serviced by an HVAC technician after closing to establish a maintenance baseline.

ERV vs. HRV: Which Does the Home Have?

Feature	ERV (Energy Recovery Ventilator)	HRV (Heat Recovery Ventilator)
Transfers heat between air streams	Yes	Yes
Transfers moisture between air streams	Yes	No
Best climate	Humid or mixed climates (transfers moisture helps manage humidity)	Cold, dry climates (doesn't add indoor moisture from outdoor air)
Common in San Diego?	More common than HRVs (San Diego's moderate humidity benefits from moisture transfer)	Less common (HRVs are more typical in heating-dominated climates)
Core type	Enthalpy wheel or flat plate with permeable membrane	Flat plate with non-permeable surface

If you're not sure which type the home has, the unit's label or nameplate will identify it. ERVs and HRVs look similar from the outside, but they manage moisture differently.

How 360 Home Inspection Evaluates ERV Systems

We test the ERV for fan operation on both sides, check filter condition, inspect the accessible core, verify condensate drainage, check ductwork connections and exterior terminations, and evaluate the control settings. Our report documents the unit's make, model, and condition, along with any deficiencies and maintenance recommendations.

For the full scope of our inspection, see our buyer's guide.

Schedule your inspection or call (858) 707-7066.

Frequently Asked Questions

Q: What is an ERV and why is it in my home?

An Energy Recovery Ventilator provides continuous mechanical ventilation (fresh air in, stale air out) while recovering energy from the exhaust air stream to precondition the incoming fresh air. It's installed to meet California's ASHRAE 62.2 ventilation requirements in tightly sealed homes without the energy penalty of exhausting conditioned air.

Q: How often do ERV filters need to be replaced?

Every 3 to 6 months depending on the environment. San Diego homes may need more frequent replacement in dusty conditions or during wildfire smoke events. Clogged filters restrict airflow and reduce the system's ventilation effectiveness.

Q: What happens if the ERV isn't maintained?

Neglected ERVs develop clogged filters, dirty cores, and blocked condensate drains. This reduces airflow, compromises indoor air quality, and can lead to moisture problems inside the unit. In severe cases, a completely neglected ERV restricts ventilation more than it helps, because the clogged system impedes airflow without providing its intended energy recovery benefit.

Q: How do I know if the ERV is working properly?

You should feel airflow at both the supply registers (fresh air entering the home) and the exhaust grilles (stale air leaving). The control should show the system is active. The unit should run without excessive noise. If the home feels stuffy despite the ERV being on, the filters or core may be clogged.

Q: Does the ERV run all the time?

Most ERVs are designed to run continuously at a low speed to provide the ASHRAE 62.2 ventilation rate, with a boost speed that activates during high moisture events (showers, cooking). Some systems operate intermittently on a timer. The control settings should be programmed to meet the home's ventilation requirement.

Q: How much does an ERV cost to replace?

An ERV unit replacement (equipment plus installation) typically costs $1,500 to $4,000 in San Diego, depending on the unit's capacity, the brand, and the complexity of the ductwork. Core-only replacement (if the unit is otherwise functional) costs $200 to $600.

Q: Is an ERV better than a simple exhaust fan for ventilation?

An ERV is more energy-efficient because it recovers energy from the exhaust air, reducing the heating and cooling cost of ventilation. It also provides balanced ventilation (equal supply and exhaust) rather than depressurizing the home the way an exhaust-only system can. The tradeoff is higher installation cost and more maintenance.

Q: Should I request ERV maintenance records from the seller?

Yes. Maintenance records (filter changes, core cleaning, service visits) indicate how well the system has been maintained. An ERV with consistent maintenance records is likely in good condition. An ERV with no records may need immediate servicing to establish a baseline.

Q: Can an ERV help with indoor humidity in San Diego?

Yes. An ERV transfers moisture between the exhaust and supply air streams, which moderates indoor humidity. In San Diego's summer, the ERV reduces the moisture content of incoming outdoor air by transferring some of it to the outgoing air stream. In winter, it retains some indoor moisture rather than exhausting it all.

Q: Does a home inspection check the ERV?

Yes. We test both fans for operation, check filter and core condition, verify condensate drainage, inspect ductwork connections, check exterior terminations, and evaluate the control settings. ERV deficiencies are documented in the report.

Final Thoughts

An ERV is one of those systems where the technology is excellent and the maintenance determines whether it actually works. A clean ERV with fresh filters and a clear condensate drain provides continuous, energy-efficient ventilation that keeps the air fresh and the humidity managed. A neglected ERV with clogged filters and a dirty core is a box in the attic that's pretending to ventilate.

Check the filters. Check the core. Check the drain. And if nobody has maintained it in a while, plan on a service call after closing to get it back to where it should be.

ERV system information and costs in this article reflect ASHRAE 62.2 requirements and San Diego market conditions as of 2026. System specifications, maintenance requirements, and costs vary by manufacturer and installation. Consult a licensed HVAC professional for system evaluation and service.