ERV and HRV Commissioning and Handover

Purpose

A heat recovery ventilator moves heat between the incoming and outgoing airstreams; an energy recovery ventilator moves heat and moisture. Either one is two fans in one box, and if those fans do not move the same amount of air the box becomes a pressurization device. Push more out than in and the house goes negative, which is the condition that makes an atmospherically vented water heater spill flue gases into the basement. Push more in than out and you drive humid summer air into wall cavities.

So commissioning is not a start-up check. It is a measured balance at the unit, a verified ventilation rate against the standard, and a proof that the appliance downstairs still drafts with the new device running at its highest speed.

Scope

Covers commissioning and handover of residential and small light commercial ERVs and HRVs, ducted independently or tied into a forced-air system: rate calculation, termination check, drain and core inspection, supply and exhaust airflow measurement, balancing, the combustion draft proof, and control setup with the occupant.

Does not cover the rough-in or the duct design, core and filter service on an existing unit, the whole-house depressurization survey where several exhaust appliances are in play, or sizing combustion air openings. Each of those has its own SOP in this library.

Roles and responsibilities

Procedure

1. Calculate the required whole-house ventilation rate before you look at the unit. Use the ventilation standard your jurisdiction has adopted, which for most residential work is ASHRAE 62.2 in the edition named by your building code; the 2019 edition sets the whole-house rate at 0.03 cfm per square foot of conditioned floor area plus 7.5 cfm per bedroom plus one. Acceptance: a required rate in cfm with the edition, floor area and bedroom count it came from. What wrong looks like: a rate taken off the unit's nameplate, which is a capacity, not a requirement. Stop rule: no adopted edition confirmed, no rate committed. Hazard: none at this step, arithmetic done at the truck.

2. Inspect both terminations before touching the unit. Confirm intake and exhaust hood separation and clearance from the driveway, dryer vent, plumbing vents and grade, against the manual and the mechanical code your jurisdiction has adopted. Acceptance: clearances met with the separation written down, both hoods clear of debris. What wrong looks like: an intake downwind of the exhaust hood, recirculating the air you paid to remove. Stop rule: a termination that cannot meet clearance is an install defect, not something to commission around. Hazard: this is ladder and roof work, so the roof access SOP governs it and the ladder is set and tied before anyone climbs.

3. Isolate power, then inspect the core, the filters and the condensate trap as installed. Acceptance: core seated with gaskets contacting, filters correct size and orientation with the airflow arrow right, condensate trap primed with water. What wrong looks like: a dry trap on a cabinet running under negative pressure, which pulls air backward through the drain and lets the pan overflow. Stop rule: no trap where the manual requires one, no commissioning until it is fitted. Hazard: prove the unit dead per NFPA 70E-2021, 120.5, with work practices at 29 CFR 1910.333(b)(2), and both fan wheels coast, so isolate under 29 CFR 1910.147 before a hand goes past a housing.

4. Measure supply airflow at the unit, in the highest speed the occupant will use. Take the reading in the outdoor-air-to-house duct at the unit, not at a room register, so the number is the unit's, not the distribution's. Acceptance: measured supply within 10 percent of the design rate from step 1. What wrong looks like: a flow hood reading at a ceiling diffuser being reported as the unit's supply, which mixes the ERV's air with the furnace's. Stop rule: outside 10 percent, do not adjust anything yet, take step 5 first, because the two readings are only meaningful as a pair. Hazard: the unit is running with panels on, so probes go through the test port and hands stay clear of the fan housings.

5. Measure exhaust airflow at the unit, at the same speed setting. Acceptance: measured exhaust within 10 percent of the design rate, and within 10 percent of the measured supply, taking the larger of the two flows as the base for that comparison. What wrong looks like: exhaust running well above supply, which is the depressurizing direction and the one that puts a natural draft appliance at risk. Stop rule: outside either gate, go to step 6 and do not proceed to the draft proof on an unbalanced unit. Hazard: same running unit, same rule about the fan housings, and the reading is taken with the cabinet closed.

6. Balance the two flows, re-measuring both after every adjustment. Use the unit's balancing dampers or speed taps, one change at a time. Acceptance: both flows within 10 percent of design and within 10 percent of each other on the larger flow, with the final pair recorded rather than the first pair plus a note. What wrong looks like: adjusting the exhaust damper and re-reading only the exhaust, since the two sides interact through the core. Stop rule: if no setting brings the pair inside both gates, the duct is the constraint and it goes back as a defect. Hazard: the cabinet is closed between readings rather than left open for convenience.

7. Restore power fully, then prove the house still drafts with the unit at high. Close up, restore the disconnect from the hinge side, then with a personal CO monitor running, put the unit on its highest speed with all other exhaust devices off and fire the atmospherically vented appliance. Acceptance: house-to-outdoor pressure no more than a few Pa more negative than the baseline you took with the unit off, no spillage at the draft hood after the appliance's normal establishment time, and 0 ppm CO rise in that zone. Hazard, and this is the step that puts a new air-moving device into service beside a combustion appliance: you are deliberately creating the negative condition, so occupants and pets stay out of that zone, the test is never left running unattended, and any CO rise ends it immediately with the appliance shut off at its gas valve and the zone opened to outdoor air. Stop rule: sustained spillage or any CO means tag the appliance, tell the occupant plainly it is not to be used, and phone the service manager from the property.

8. Set the control the occupant will actually live with, and hand it over at the unit. Set the ventilation mode, any recirculation or defrost setting the manual specifies for your climate, and the timer or humidity control. Acceptance: the occupant can say out loud what the control does, where the filters are, and when they get changed. What wrong looks like: a unit left in a boost mode nobody understands, which gets switched off in January and never switched back. Stop rule: if the occupant cannot repeat it back, it gets shown again rather than written on a card. Hazard: none at this step, a conversation held with the panels back on.

When the site does not match

Design rate not supplied by anyone: run step 1 yourself and write the derivation on the sheet, because a commissioning record with no target is numbers with nothing to compare against. Unit ducted into a forced-air return: the supply reading is still taken in the ERV's own duct, with the furnace blower's state recorded beside every reading. Combustion appliance present but gas off at the meter: commissioning stops at step 6, the sheet is marked incomplete with the reason, and the draft proof is booked as a return visit rather than assumed.

The record this produces

The commissioning sheet carries: the required rate with the standard edition, floor area and bedroom count behind it; unit model and serial; both termination clearances as measured; core, filter and trap condition; supply and exhaust airflow at the unit with the speed setting, as a final pair; both percentage deviations, from design and from each other; the pressure change and spillage result at the combustion appliance with the appliance named; the control settings left in place; and the filter change interval.

Two people use it. The service tech at the first core and filter service, who re-measures against this pair and can see whether the unit drifted or the duct loaded. And the shop, if a customer later reports a cold draft or a spilling water heater, because a dated balanced pair plus a clean draft proof separates a commissioning defect from something that changed later.

Worked pass: 2,100 square feet, three bedrooms, new HRV, gas water heater in the basement

Atmospherically vented water heater sits in the same basement as the HRV.

Step 1. 0.03 times 2,100 square feet is 63 cfm. 7.5 times four, being three bedrooms plus one, is 30 cfm. 63 plus 30 is a required rate of 93 cfm, derived under the 2019 edition of ASHRAE 62.2 as adopted locally. Unit is rated 120 cfm at the manufacturer's stated external static, so it has room.

Step 2. Hood separation measures 8 ft, above the manual's stated minimum, both hoods clear, intake 12 ft from the dryer vent. Pass.

Step 3. Core seated, filters correctly oriented, condensate trap dry. Trap primed with water before proceeding. Pass after correction.

Step 4. Supply measures 90 cfm against a 93 cfm design. 90 divided by 93 is 0.968, so 3.2 percent low, inside 10 percent. Reading held, step 5 taken before any adjustment.

Step 5. Exhaust measures 118 cfm. 118 divided by 93 is 1.269, so 27 percent above design. Balance check on the larger flow: 118 minus 90 is 28 cfm, and 28 divided by 118 is 23.7 percent apart, outside the 10 percent gate. Step 5 fails both gates and takes its stop rule.

Step 6. Cause found at the supply balancing damper, left near-closed from rough-in, with the exhaust damper wide open. Supply damper opened, exhaust damper trimmed, both sides re-read after each change. Final pair: supply 90 cfm, exhaust 94 cfm. Against design, 90 divided by 93 is 3.2 percent low and 94 divided by 93 is 1.1 percent high. Against each other, 94 minus 90 is 4 cfm, and 4 divided by 94 is 4.3 percent, inside 10 percent. Pass.

Step 7. Baseline basement-to-outdoor pressure with the unit off, minus 1.5 Pa. With the HRV on high and no other exhaust running, minus 2.5 Pa, a change of 1 Pa. Water heater fired, no spillage at the draft hood after 60 seconds, CO monitor holds 0 ppm in the zone. Pass.

Step 8. Set to continuous low with a boost on the bathroom switch, defrost per the manual for this climate. Occupant repeated back where the filters are and when they get changed. Pass.

Signed off as "runs and moves air," this house goes into winter with 28 cfm more leaving than arriving, in a basement with a natural draft water heater.

References

• ASHRAE 62.2, in the edition your jurisdiction has adopted through its building code, for the whole-house ventilation rate and how it is derived
• Manufacturer's installation manual and HVI-certified airflow ratings for the specific unit, read at the external static the rating was taken at
• The mechanical code your jurisdiction has adopted, for termination clearances and separation
• 29 CFR 1910.333(b)(2) with NFPA 70E-2021, 120.5 for live-dead-live; 29 CFR 1910.147 for isolating the fan wheels
• See related: the ERV and HRV core and filter service SOP, the combustion air verification SOP, and the roof access and fall protection SOP