HVAC Mechanical Ventilation Guide — ASHRAE 62.2 Sizing, ERV vs HRV, Climate Strategy, Installation

Both ERVs (Energy Recovery Ventilators) and HRVs (Heat Recovery Ventilators) transfer heat between incoming outdoor air and outgoing exhaust air, recovering 60-85% of the heating/cooling energy that would otherwise be lost to ventilation. The difference: HRVs transfer only SENSIBLE heat (temperature); ERVs transfer BOTH sensible heat AND LATENT energy (moisture). In summer cooling: ERVs reduce both incoming heat and humidity, lowering AC load substantially. In winter heating: ERVs retain indoor humidity (preventing the very dry air that pure HRVs allow) while still recovering heat. The catch: ERVs that transfer moisture in both directions can also transfer pollutants if the exchanger media is permeable to specific contaminants — high-quality polymer membrane exchangers are highly selective (water vapor permeable, pollutants restricted). HRV recommended for: very cold climates with low outdoor humidity (Zones 6-8) where moisture transfer in winter would over-humidify; homes with high indoor moisture loads (lots of bathing, cooking, plants). ERV recommended for: hot/humid climates (Zones 1-4A) where summer latent recovery is large savings; cold/dry climates where winter humidity retention is valuable. Most US residential favors ERV.

Per ASHRAE Standard 62.2-2022: total continuous ventilation rate (CFM) = (0.03 × conditioned floor area in ft²) + (7.5 × number of bedrooms + 1). For a 2,000 ft² home with 3 bedrooms: 0.03 × 2,000 + 7.5 × 4 = 60 + 30 = 90 CFM continuous. ASHRAE 62.2 also specifies local exhaust requirements: kitchen 100 CFM intermittent OR 25 CFM continuous; bathrooms 50 CFM intermittent OR 20 CFM continuous each. The total ventilation rate is met by some combination of: natural infiltration credit (per 62.2 calculation based on home tightness and climate), local exhaust running continuously, and dedicated mechanical ventilation system. The simplification: design the mechanical ventilation system to deliver the full 62.2 rate; treat any natural infiltration as a bonus rather than a credit. This produces a robust ventilation strategy that doesn't depend on the home being as leaky as assumed.

Depends on the range hood's CFM and your home's tightness. IRC 2021 Section M1503.4 requires make-up air for any range hood exhaust rated 400 CFM or higher; some local jurisdictions lower the threshold to 300 CFM. The mechanism: high-CFM range hoods create substantial negative pressure indoors when running. In tight construction (≤3 ACH50), the negative pressure can pull combustion byproducts back down the gas water heater or furnace flue (backdrafting), creating CO hazards. Make-up air systems provide a controlled outdoor air pathway to neutralize the negative pressure when the hood runs. Two strategies: (1) Passive make-up air — a damper opens automatically when the range hood activates, allowing outdoor air in (cheapest but introduces unconditioned air); (2) Active make-up air — a fan supplies tempered outdoor air through a HVAC integration (more expensive but maintains comfort). Critical for any home with gas water heater + gas furnace + atmospherically-vented combustion appliances near the range hood. Discuss with the HVAC contractor at install.

Yes, with planning. Three integration patterns: (1) STANDALONE: dedicated ERV/HRV with its own ductwork and fans, completely independent of HVAC. Best for retrofits where central HVAC ductwork can't be easily modified. (2) PARALLEL: ERV/HRV ductwork run in parallel with HVAC; supply air dumps into supply trunks; exhaust air pulled from exhaust grilles in baths. Requires HVAC and ventilation to coordinate. (3) INTEGRATED: ERV/HRV outdoor-air duct supplies into HVAC return plenum; HVAC blower handles distribution. Simpler ductwork but requires HVAC blower to run continuously (or at least when ventilation runs). For new construction, integrated is usually most efficient. For retrofit, standalone is often easiest. Manufacturers (Panasonic, Broan, Lifebreath, Renewaire, Greenheck, Fantech) publish installation guides for each integration pattern. Capacity considerations: typical residential ERV/HRV is 100-300 CFM continuous, well within most residential HVAC system airflow capacity.

Depends on climate severity and ventilation hours. Math example: 2,000 ft² home in Zone 5 (Boston) running 90 CFM continuous ventilation (per ASHRAE 62.2). Without ERV, that 90 CFM × 7,200 cooling degree-days/year × 1.08 BTU/hr/CFM/°F × 0.000293 kWh/BTU = significant cooling+heating load. With 75% effective ERV, recover ~75% of that energy. For typical Zone 5 climate the energy savings are typically $150-400/year. ERV equipment + install cost typically $1,500-4,000 ($2,500 average residential). Simple payback: 6-15 years, dropping faster with rising energy prices. IRA 25C tax credit (covered as part of heat pump category in some installations) can apply if the ERV is part of a qualifying heat pump installation. For mild climates (Zones 1-2 dry) the ERV math is weaker — minimal latent and modest sensible recovery, longer payback. For severe climates (Zones 5-7) ERV math is strongest. Beyond direct savings: ERV preserves IAQ in tight construction where natural infiltration is inadequate, which has health and comfort value beyond direct dollars.

EXHAUST-ONLY (the cheapest 62.2-compliant option): a continuously-running fan (often a bathroom exhaust on a low-speed timer) pulls air out of the home; outdoor air infiltrates passively through whatever leakage paths exist to replace it. Cost: $50-200 to retrofit. Cons: negative indoor pressure pulls outdoor air through random locations including foundation (radon), soil contamination, attic, walls (insulation off-gassing). Not recommended for tight construction or radon-zone homes. BALANCED VENTILATION: equal supply and exhaust airflow, maintained by a fan delivering outdoor air and a matched fan removing indoor air. No net pressure change indoors. Cost: $300-1,000 for basic balanced; $1,500-4,000 for ERV/HRV. Pros: controlled supply air entry (from a designated location, filtered before entry); no random infiltration paths; preserves envelope integrity. Recommended for: any tight construction (post-2010 typical), radon-zone homes, homes with attached garages, IAQ-conscious households. ASHRAE 62.2 permits both strategies; ENERGY STAR Single-Family New Homes requires balanced for higher tier certifications.

Typical residential ERV/HRV operates at 30-45 dBA at the indoor head unit when running at design CFM — quieter than typical bathroom exhaust fan (which is 45-65 dBA), about the level of light rainfall. The fan is the only noise source; the heat exchanger itself is silent. ERV/HRV manufacturer data sheets publish sound power values; the better units operate below 1.0 sone at the indoor diffuser. For comparison: HVAC blowers typically produce 45-55 dBA at supply registers. ERV is usually quieter than HVAC. Considerations: locate the ERV/HRV away from bedrooms or living spaces where noise is unwelcome (attic, mechanical room, garage). Acoustic-rated duct between equipment and indoor diffusers reduces noise transmission. For occupants who notice equipment noise, ASHRAE 62.2 allows lower CFM intermittent operation as long as effective CFM (averaged across the day) meets the rate.

Modest but specific. (1) FILTERS: typically a coarse pre-filter on the outdoor supply side (every 3-6 months) and sometimes a higher-MERV filter on the indoor exhaust side (every 6-12 months). Manufacturer data sheets specify. Skipping filter changes leads to coil/exchanger fouling. (2) HEAT EXCHANGER: annual visual inspection; clean with vacuum or mild detergent every 1-3 years depending on use. Polymer membrane exchangers should not be saturated with cleaners — follow manufacturer instructions. (3) CONDENSATE DRAIN (ERV models with condensate provision): check drain operation seasonally. (4) FAN MOTORS: typically maintenance-free for 10-15 years; replace at end of service life. (5) CONTROLS: verify thermostat or controller programming annually. Total annual maintenance time: 30-60 minutes for typical residential. Maintenance cost (if professional): $100-200/year if added to regular HVAC contract.