How to Maintain a Heat or Energy Recovery Ventilator (HRV/ERV)

TL;DR: Heat recovery ventilators (HRVs) and energy recovery ventilators (ERVs) need filter replacement every 3-6 months, core cleaning once a year, drain pan checks in humid months, and an annual pro inspection. Neglect these and efficiency drops 30% or more while your system recirculates dust and allergens. The four maintenance tasks—filters, core, drains, and balance—take under an hour per year and preserve the 70-80% energy recovery you paid for.

_Last reviewed: July 2026 · 6 min read_

Whole-house ventilation systems like HRVs and ERVs exhaust stale indoor air while bringing in fresh outdoor air—and they recover 70-80% of the heat (or cooling) from the outgoing stream. But clogged filters and dirty heat-exchange cores cut that recovery rate in half, turning a premium ventilation system into an expensive source of drafts and dust. If you've noticed musty smells, condensation on windows, or higher heating bills, the ventilator probably needs attention.

Okoniq Property Hub logs filter changes, core cleanings, and service dates so you never miss the maintenance window that keeps recovery efficiency above 70%.

How often should you change HRV and ERV filters?

Change or clean filters every 3-6 months depending on local dust levels and whether you have pets. Most residential HRVs and ERVs use washable foam or pleated filters rated MERV 6-8—check your manual because some units have disposable filters that must be replaced. The incoming (outdoor) filter catches pollen and particulates; the outgoing (indoor) filter traps cooking grease, pet dander, and lint. When either clogs, the blower works harder and airflow drops by 20-40%, which reduces heat recovery and can trigger a high-static alarm.

Mark your calendar for January and July; those months bracket heating and cooling seasons when the system runs hardest. Remove both filters, rinse foam filters under warm water until the runoff is clear, then let them air-dry completely before reinstalling. If you have pleated disposable filters, replace them when they're visibly gray or if you can't see light through the media. A $15 filter change twice a year preserves $200-300 in annual heating savings by keeping recovery efficiency near 75%. Track the task in Okoniq's maintenance log alongside your furnace and AC checks—ventilators are part of the same indoor-air system.

When and how do you clean the heat-exchange core?

Clean the core once a year, ideally in early fall before heating season. The core is a stack of thin aluminum or plastic plates (in an HRV) or a polymer membrane wheel (in an ERV) where exhaust and supply air pass within millimeters of each other without mixing. Dust, cooking vapor, and pollen build a film on those surfaces; after 12 months the film can reduce heat transfer by 30% even if filters are clean. Your manual will show how to slide the core out—most units have two thumb screws and a handle. Rinse the core gently with a hand-held shower head or garden hose set to low pressure; never use a pressure washer or you'll bend the fins. Let it dry completely (24 hours in a warm room) before reinstalling.

Some cores are coated with an antimicrobial layer that degrades if you use dish soap or bleach—stick to plain water unless the manual permits a mild detergent. If you see black spots or a sour smell, you may have mold growth from condensation; in that case spray the core with a 50/50 white-vinegar solution, let it sit 10 minutes, rinse, and dry. Persistent mold means the unit is running in an unbalanced mode (too much exhaust or supply) or the outdoor intake is pulling air from a damp crawlspace—call an HVAC tech to measure flow rates and rebalance. Log core cleaning dates in Okoniq so you can prove annual care if you sell the house; buyers with allergies pay attention to indoor air quality maintenance.

What should you check in the condensate drain and pan?

Check the drain pan and trap every 3 months in humid climates, twice a year in dry climates. HRVs produce condensation when cold outdoor air meets warm exhaust air; ERVs condense moisture from exhaust air in cooling mode. That water drips into a shallow pan and exits through a 3/4-inch drain line, usually routed to a floor drain or condensate pump. If the drain clogs with algae or dust, water backs up into the unit, triggers a safety shutoff, and can overflow onto the floor or ceiling below. Pull the pan (it slides out like a drawer on most models), dump any standing water, and scrub the pan with a sponge and white vinegar to remove biofilm.

Pour a cup of water down the drain line to confirm flow—if it backs up, disconnect the line and flush it with a wet/dry vac or a hand pump. Some units have a U-trap that can dry out in winter when the system runs less; if you smell sewer gas, pour a tablespoon of vegetable oil into the trap to seal the air gap without evaporating. The same principle applies to your AC condensate line—algae loves dark, damp tubes. If your HRV shares a condensate pump with the furnace or AC, inspect the pump reservoir and float switch at the same time; a stuck float can flood both systems.

How do you know if airflow is balanced and ducts are sealed?

Hire an HVAC tech every 2-3 years to measure supply and exhaust CFM (cubic feet per minute) and verify balance within 10%. HRVs and ERVs are designed to move equal volumes of air in and out; if exhaust exceeds supply by more than 10 CFM the house depressurizes and can backdraft combustion appliances, while excess supply pressurizes the house and forces humid air into wall cavities. The tech will use a flow hood or anemometer at each register, adjust dampers in the ductwork, and seal any leaks with mastic (never duct tape, which degrades in 2-3 years).

Unbalanced flow also signals duct leaks—if the supply duct pulls air from an unconditioned attic, you lose the energy-recovery benefit and introduce dust or mold spores. The same check applies to your main HVAC duct system; leaky ducts waste 20-30% of conditioned air. Budget $150-250 for a balance check and minor duct sealing; the cost pays back in one heating season if the system was more than 15% out of balance. Document the service date and CFM readings in Okoniq so the next owner or tenant knows the system was professionally tuned.

Should you run the ventilator continuously or on a schedule?

Run the ventilator 24/7 at low speed in tightly built homes (ACH50 < 3), and use a timer or boost mode for intermittent operation in older homes with natural air leakage. Modern building codes require continuous ventilation at 0.35 air changes per hour to dilute indoor pollutants—cooking fumes, VOCs from furniture, radon, and CO₂. If your HRV or ERV has a low/medium/high switch, low speed typically moves 50-75 CFM, enough for continuous background ventilation in a 1,500-2,000 sq ft home. Boost to medium or high for 30 minutes after cooking, showering, or when the house is full of guests.

Running continuously costs $5-10 per month in fan electricity but recovers $40-60 in heating and cooling by preconditioning incoming air. If you shut the system off to save power, you lose the recovery benefit and indoor humidity swings, causing condensation on windows in winter and mustiness in summer. Some units have a built-in humidistat or integrate with a smart thermostat (Ecobee, Nest) to ramp speed based on indoor RH%; set the target to 35-45% RH in winter and 50-55% in summer. Track runtime and energy use in Okoniq alongside your baseboard heater or furnace logs—ventilation is part of your total heating load.

FAQ

How much does it cost to replace an HRV or ERV core?

Replacement cores cost $200-600 depending on unit size and whether it's aluminum (HRV) or polymer membrane (ERV). Most cores last 10-15 years if cleaned annually; the blower motor and controls typically fail first. If a core is damaged by freezing or pressure-washing, call the manufacturer for a part number before ordering—aftermarket cores rarely match the original efficiency.

Can you install an HRV or ERV yourself?

Installing a whole-house HRV or ERV requires ductwork, electrical, and exterior wall penetrations—hire a licensed HVAC contractor unless you have all three skillsets. A typical install costs $2,500-5,000 including the unit, ducts, dampers, and controls. DIY errors—undersized ducts, unbalanced dampers, no condensate drain—void warranties and can depressurize the house enough to backdraft a water heater or furnace.

What's the difference between an HRV and an ERV?

An HRV (heat recovery ventilator) transfers heat but not moisture; an ERV (energy recovery ventilator) transfers both heat and water vapor. Use an HRV in cold-dry climates where winter indoor humidity is too low, and an ERV in hot-humid climates where summer outdoor air is muggy. Both recover 70-80% of the energy in the exhaust stream; the choice depends on your climate and whether you need humidity control.

Why does my HRV smell musty or moldy?

A musty smell usually means the core or drain pan has biofilm or mold. Pull the core and rinse it with a 50/50 vinegar solution, clean the drain pan, and check that the condensate line isn't clogged. If the smell persists, the outdoor intake may be drawing air from a crawlspace, attic soffit, or area near a bathroom vent—relocate the intake to a clean exterior wall at least 10 feet from exhaust vents and 3 feet from the ground.

Do HRVs and ERVs work with central AC and furnace systems?

Yes—most HRVs and ERVs tie into the main return plenum so the HVAC blower distributes fresh air throughout the house. Some installers add a damper and pressure switch so the ventilator runs only when the furnace blower is on; this saves fan energy but reduces fresh air during mild weather when the HVAC is idle. A better setup is a dedicated low-speed blower in the ventilator and separate supply ducts to bedrooms and living areas, ensuring continuous ventilation independent of heating and cooling calls.

This is educational information, not HVAC design or building-code advice. Consult a licensed HVAC contractor for system sizing, duct design, and code compliance in your jurisdiction.