ERV and HRV Core and Filter Service

Purpose

An ERV or HRV core is a resistance in two airstreams at once. Load it, or refit it badly, and both flows change, which means a service visit can leave a house more out of balance than it was when the tech arrived. That is the failure this procedure prevents: the unit runs, both fans spin, the customer is happy, and the exhaust is now pulling harder than the supply in a basement with a natural draft water heater.

The other failure is destroying the core. Enthalpy cores and heat-only cores are cleaned by different methods, and washing a core that the manufacturer says to vacuum only turns a service into a parts sale. Read the manual for that model before water touches anything.

Scope

Covers scheduled and complaint-driven core and filter service on residential and small light commercial ERVs and HRVs: record review, isolation, filter and core removal, cleaning by the manufacturer's method, drain and damper service, reassembly and restoration, and the post-service balance check against the commissioned pair.

Does not cover first commissioning or balancing a unit that has never been balanced, which belongs to the ERV and HRV commissioning SOP and supplies the pair this procedure checks against. Does not cover duct cleaning, mold remediation, or any application of an antimicrobial product into the airstream.

Roles and responsibilities

Procedure

1. Read the commissioning sheet and the last service record before you open the cabinet. You need the commissioned supply and exhaust flows in cfm and the interval on file. Acceptance: both flows and the interval written on today's ticket before any panel comes off. What wrong looks like: a service with no baseline, which cannot tell you whether today's readings are drift or normal. Stop rule: no commissioning pair on file means this visit measures and records a new baseline before cleaning anything, and says so on the sheet. Hazard: none at this step, paperwork read at the truck.

2. Isolate power and prove it dead, remembering both fan wheels coast. Prove the meter on a known live source, prove the conductors dead, prove the meter live again per NFPA 70E-2021, 120.5, with work practices at 29 CFR 1910.333(b)(2), then isolate the unit under 29 CFR 1910.147. Acceptance: 0 volts at the unit's supply terminals and both wheels at rest before a hand goes past a housing. What wrong looks like: pulling the plug on a cord-connected unit and reaching straight in while a wheel is still turning. Stop rule: a wheel still turning is a wheel you wait for, and if the unit will not stay off, the branch circuit gets locked out at the panel.

3. Withdraw the filters and bag them at the unit. Acceptance: filters out, condition graded as clean, loaded, collapsed or bypassing, and sealed in a bag at the cabinet rather than carried through the house. Hazard, and it sits on the pull rather than the access: a loaded filter releases its collected dust as an airborne cloud when flexed, so it comes out slowly and straight into the bag, and where the media is soaked, matted or shows visible growth, the control for that route is a respirator under a written program per 29 CFR 1910.134, not a comfort mask, and the vacuum used nearby is HEPA-filtered so it captures fines rather than re-emitting them. Stop rule: filters found collapsed or bypassing means the interval is wrong and step 8 shortens it.

4. Withdraw the core and inspect it before deciding how to clean it. Acceptance: core out, both faces inspected, with matting, deformed media, delamination, torn gaskets or standing moisture each recorded as present or absent. What wrong looks like: a core pulled and hosed without an inspection, which loses the one chance to see why it fouled. Stop rule: a delaminated, crushed or visibly grown-through core is condemned, not cleaned, and the service manager is called before the old one leaves the site. Hazard, second disturbance of the same route: a fouled core sheds loose material as it slides out, so it comes straight into a bag or a lined tote at the unit, with the same respiratory control as step 3 where the fouling is heavy.

5. Clean the core by the method the manufacturer's manual names for that exact model, and by no other. Heat-only cores are commonly washable; paper-based enthalpy cores are commonly vacuum-only and are destroyed by wetting. Acceptance: the manual's named method carried out, with the method written on the ticket. What wrong looks like: a wetted enthalpy core, which delaminates and then leaks exhaust air into the supply for the rest of its life. Stop rule: if the manual is not available for that model, the core is vacuumed with a HEPA-filtered vacuum and nothing else, and the shop gets the manual before the next visit. Hazard: no biocide, sanitizer or disinfectant goes into this airstream unless that product's own label lists this use, because applying a pesticide in a way its labeling does not permit is prohibited under FIFRA, and the label is the instruction, not the sales sheet.

6. Service the drain pan, re-prime the trap, and stroke the damper. Clean the pan, refill the trap, and cycle the recirculation or defrost damper through full travel. Acceptance: a poured cup clears the drain within a minute, the trap holds water at rest, and the damper reaches both end positions and seats. What wrong looks like: a damper that strokes but does not seat, which lets outdoor air bypass the core all winter. Stop rule: a damper that will not seat is repaired or the unit is left off. Hazard: pan water in a unit that has been running wet is biologically active, so gloves stay on and the pan is wiped rather than sprayed, since spraying is what puts it in the air you are breathing.

7. Reassemble, restore power, and re-prove the protections you disturbed. Refit core, filters and panels first, then restore the disconnect standing to the hinge side rather than square in front. Acceptance: both fans start, opening the service door stops them within the manual's delay, the drain runs during operation, and where an atmospherically vented appliance shares the house, it is fired with the unit at high and shows no spillage at the draft hood after its normal establishment time with 0 ppm CO rise. Hazard: this is the step that puts motion and negative pressure back into a house with people in it, so panels are on before the handle moves, the room is clear, and any CO rise ends the test with the appliance shut off at its gas valve and the zone opened to outdoor air. Stop rule: spillage or CO means tag the appliance, tell the occupant it is not to be used, and phone the service manager from the property.

8. Re-measure both flows against the commissioned pair and set the next interval. Acceptance: supply and exhaust each within 10 percent of the commissioned figure, and within 10 percent of each other taking the larger flow as the base. Interval rule: filters found collapsed, matted or bypassing before the scheduled date cuts the interval to its midpoint, reviewed again at the next service. What wrong looks like: a post-service pair recorded from memory of the commissioning sheet rather than measured. Stop rule: outside either gate, the cause is a mis-seated core, a wrong filter or a gasket, and it is found before the ticket closes. Hazard: readings taken with panels on and probes through the ports, never with the door held ajar.

When the site does not match

Replacement core not on the truck: the unit runs coreless only if the manufacturer permits it, which many do not, and otherwise it is switched off at the disconnect with the customer told plainly that the house has no mechanical ventilation until the part lands. Filters not a stocked size: fit nothing rather than the nearest size, because an undersized filter bypasses at the frame and loads the core faster than no filter at all. Unit found unbalanced on arrival, before any work: record the arrival pair separately from the post-service pair, or nobody can tell later which readings belong to your visit.

The record this produces

The service sheet carries: the commissioned pair pulled from the file; filter condition graded, with sizes; core condition against each of the five inspection items; the cleaning method used and the manual it came from; drain, trap and damper results; the door switch and combustion draft proof results; the post-service supply and exhaust pair with both deviations, from the commissioned figure and from each other; and the next interval with the reason if it changed.

Two people use it. The next service tech, who can read three visits of filter condition and see whether this house loads media in nine months or eighteen. And the service manager, who needs the arrival and post-service pairs side by side if a customer reports a draft or a spilling appliance after the visit.

Worked pass: 2,600 square foot house, ERV three years in, humid climate, annual interval

Commissioning sheet on file reads supply 96 cfm, exhaust 99 cfm.

Step 1. Both flows and a 12 month interval written on today's ticket. Last service 12 months ago. Pass.

Step 2. Meter proved live, unit terminals read 0.0 volts, meter re-proved live, both wheels stopped before opening. Pass.

Step 3. Filters are matted flat and pulling away from the frame at one corner, so they are bypassing. Bagged at the unit. Graded as collapsed and bypassing, which flags the interval for step 8.

Step 4. Core withdrawn. Both faces matted with lint. Along the top edge the paper media has separated from its spacers over roughly a third of the face. Recorded as delamination present.

Step 5. Manual for this model states vacuum only, no water. The delamination is not a cleaning question. Step 5 fails and takes its stop rule: the core is condemned rather than cleaned. Service manager called from the property before the old core left the site. History pulled: the previous service two years ago recorded the core as "washed and refitted," which is the method this manual prohibits and the reason the media separated. Replacement core fitted the same day from stock.

Step 6. Pan cleaned and wiped, trap refilled and holding, damper reaches both end positions and seats. Poured cup clears in about 30 seconds. Pass.

Step 7. Reassembled, disconnect closed from the hinge side. Both fans start. Service door opened: both stop in about 2 seconds. Gas water heater fired with the ERV on high, no spillage at the draft hood after 60 seconds, CO monitor holds 0 ppm. Pass.

Step 8. Supply measures 94 cfm; against the commissioned 96, that is 2 cfm, and 2 divided by 96 is 2.1 percent. Exhaust measures 97 cfm; against the commissioned 99, that is 2 cfm, and 2 divided by 99 is 2.0 percent. Balance on the larger flow: 97 minus 94 is 3 cfm, and 3 divided by 97 is 3.1 percent. All three inside 10 percent. Pass. Filters were collapsed at 12 months, so the interval is cut to its midpoint, 6 months, and the reason is written beside it.

References

• Manufacturer's service manual for the specific core, which is the only authority on whether that core may be wetted
• ASHRAE 62.2, in the edition your jurisdiction has adopted, for the whole-house rate the commissioned pair was set against
• 29 CFR 1910.333(b)(2) with NFPA 70E-2021, 120.5 for live-dead-live; 29 CFR 1910.147 for isolating both fan wheels; 29 CFR 1910.134 for respiratory protection under a written program when disturbing loaded media
• FIFRA, which makes use of a pesticide in a manner inconsistent with its labeling unlawful, and therefore makes the product label the instruction for any antimicrobial in an airstream
• See related: the ERV and HRV commissioning SOP, which produces the pair this service is measured against