ERV vs HRV and makeup air for New York homes

A tighter house needs planned ventilation

Air sealing, new windows, spray foam and dense-pack insulation cut the accidental air exchange that once ventilated older houses. Moisture, carbon dioxide, odors, cooking particles and, with gas ranges, nitrogen dioxide now stay indoors longer. Energy codes pair tighter construction with whole-house mechanical ventilation, so a gut renovation of a brownstone, a Queens two-family or a Long Island cape should carry a ventilation plan before walls and ceilings close.

Three different rate rules can apply to a New York home. ASHRAE Standard 62.2, the national reference, requires 0.03 cfm per square foot of floor area plus 7.5 cfm per person, with occupancy taken as the number of bedrooms plus one; a 2,000 square foot house with three bedrooms needs about 90 cfm. The New York State Residential Code, which governs Long Island and most of the state, uses the IRC formula of 0.01 cfm per square foot plus 7.5 cfm per person, or about 50 cfm for the same house. The NYC Mechanical Code (opens an external site) (Table 403.3.1.1) sets 0.35 air changes per hour but not less than 15 cfm per occupant, which for that house with 8-foot ceilings is about 93 cfm. We design to the rule that governs the property and, where the owner wants it, to the higher ASHRAE figure.

ASHRAE 62.2 allows a credit for measured air leakage in detached single-family homes, based on a blower-door test, but not for apartments in multifamily buildings. The model codes and ASHRAE 62.2 also allow intermittent operation if the fan is sized up to deliver the same daily volume.

Exhaust-only, supply-only or balanced

Supply-only systems and humidifiers combine poorly, because slight pressurization drives humid indoor air into cold wall and attic cavities. Balanced ventilation avoids that and is what we recommend for most tight homes.

ERV or HRV

Both units exchange heat between outgoing and incoming air. An ERV also transfers part of the moisture. In a New York winter that keeps some indoor humidity in the house, which helps homes that run dry and can reduce the need for a humidifier; in summer it reduces the moisture carried in by ventilation air. An ERV is not a dehumidifier, and air conditioning or a dehumidifier is still needed in humid weather. Green Building Advisor (opens an external site) describes the winter moisture benefit as real but modest.

An HRV removes indoor moisture in winter, which suits only houses with too much winter humidity, such as a small, very tight house with a large family. Our default is an ERV for New York City and Long Island, with the choice made case by case for colder upstate homes, where core frost and defrost cycles matter more.

• Dedicated ducts give the best results. Connecting to furnace ducts is possible but requires an interlock with the blower and careful balancing.
• The outdoor intake must be separated from exhaust outlets, vents and other contaminant sources, at distances set by the applicable mechanical code.
• Airflow is balanced with a flow measurement after installation, so that every room receives its share.
• Filters are cleaned or replaced on schedule, and the unit is placed where it can be serviced.
• Apartments can use compact ceiling ERVs or through-wall single-room units, subject to co-op or condo board approval for façade openings and, in landmarked buildings, Landmarks Preservation Commission review of visible louvers.

Range hoods and makeup air

High-heat cooking, wok cooking included, calls for a ducted hood. In a tight house or apartment a hood cannot move its rated airflow unless the same volume of air can enter. Without makeup air a large hood pulls the house into strong negative pressure: doors whistle, odors arrive from neighboring units, and natural-draft water heaters or boilers can spill combustion gases into the home.

Outside New York City, the residential code is based on the International Residential Code. The model IRC requires makeup air for kitchen exhaust above 400 cfm, and since its 2018 edition only where the home has natural-draft fuel-burning appliances, with a damper interlocked with the hood. We confirm the current New York State text for each project.

New York City's 2022 Mechanical Code takes a different approach from the IRC. Section 505.2 (opens an external site) does not use a cfm trigger: wherever a kitchen exhaust hood is required under Chapter 4, makeup air must be provided at the Table 403.3.1.1 rate through an opening with a motorized closure that runs with the hood. Earlier editions of the city code used the 400 cfm threshold, and much online advice still quotes it. The code also permits listed recirculating hoods in dwellings when they are installed to the manufacturer's instructions and the kitchen has the general ventilation Chapter 4 requires.

• Size the hood to the cooking, not to the showroom. Rated cfm is measured at zero static pressure, and a long apartment duct with elbows and a wall cap often delivers about half.
• Capture matters as much as fan size. A deep canopy that extends beyond the cooktop often outperforms a larger fan with a shallow hood.
• Makeup air enters through a motorized damper interlocked with the hood, filtered, and tempered in winter so that cold air does not spill onto the cook.
• Ducted hoods need smooth metal ducts and a backdraft damper. Opening a window is not a code-compliant makeup-air solution.

Bath exhaust

Model codes call for at least 50 cfm intermittent or 20 cfm continuous exhaust per bathroom, and 100 cfm intermittent or 25 cfm continuous for kitchens. The NYC Mechanical Code has its own table, which we follow on city projects.

• Duct the fan to the outdoors, never into the attic or a soffit. Bath fans vented into the attic are a common cause of attic mold in Long Island capes.
• Use a short, smooth duct with a backdraft damper and a quiet fan with a low sone rating.
• Control the fan with a humidity sensor or timer so it runs for about 20 minutes after a shower.
• In apartment buildings, windowless bathrooms often share a roof exhaust shaft. Registers clogged with paint or dust are common, and booster fans cannot be added to a shared shaft without building approval.

Combustion safety and radon

Tightening a house that still has natural-draft gas appliances takes care. The standard method for combustion air (opens an external site) provides at least 50 cubic feet of room volume per 1,000 Btu/h of appliance input, so a 40,000 Btu/h water heater and an 80,000 Btu/h furnace together need about 6,000 cubic feet. Before a large hood or exhaust fans go into such a home, the appliance area gets a worst-case depressurization test, and sealed-combustion or electric replacements are worth considering.

Radon is a separate concern. On the EPA Map of Radon Zones (opens an external site), all five boroughs, Nassau, Suffolk, Westchester and Rockland are Zone 3, the lowest predicted potential, while Orange, Putnam, Dutchess and much of upstate New York are Zone 1. EPA advises testing every home regardless of zone, fixing at 4 pCi/L or higher and considering a fix between 2 and 4 pCi/L. Exhaust-only ventilation can increase soil-gas entry. Radon testing and mitigation are performed by a certified radon professional, and we coordinate the ventilation design with their findings.

Filtration and a starting point by home type

EPA recommends a filter rated at least MERV 13 (opens an external site), or as high as the system fan and filter slot allow. A 1-inch MERV 13 filter in an undersized return restricts airflow and can cause coil icing, noise and higher energy use; a 4 or 5 inch media cabinet usually solves this. ERV filters protect the core and need upgrading if they are also meant to clean the air. Homes without ducts rely on portable HEPA purifiers, which earned their place on the 2023 wildfire smoke days.

A kitchen with a powerful hood, a gut renovation or a newly tightened house is the moment to design ventilation. We design ERV or HRV systems, range-hood makeup air and bath exhaust to the code that applies to your property, handle board and permit requirements, and install the work with our licensed HVAC partner.