Ducting HRVs and ERVs: A Complete Guide to Proper Installation, Performance, and Home Fit

If you’re building a new energy-efficient home, retrofitting a tight older property, or upgrading your indoor air quality, you’ve likely weighed the benefits of HRVs (Heat Recovery Ventilators) and ERVs (Energy Recovery Ventilators). But far too many homeowners focus solely on choosing between the two units—and overlook the critical role ofducting in making these systems work effectively.

Ducting is the circulatory system of your HRV or ERV; even the highest-quality unit will underperform, waste energy, or fail to deliver fresh air evenly if paired with poorly designed, sized, or installed ductwork. Whether you’re working with a contractor or planning a DIY ventilation upgrade, understanding how to duct HRVs and ERVs properly is non-negotiable for long-term efficiency, comfort, and air quality.

In this guide, we’ll break down everything you need to know about ducting HRVs and ERVs, from core design principles and key differences between HRV/ERV duct requirements to common mistakes to avoid and pro tips for optimal performance.

First: The Basics of Ducting for HRVs and ERVs

Unlike standard HVAC ductwork that distributes heated or cooled air, HRV and ERV ducting serves a dual purpose: it pulls stale, polluted air out of your home’s “wet” or high-occupancy spaces and delivers filtered, fresh outdoor air to living areas like bedrooms, living rooms, and offices. Both systems rely on balanced ventilation, meaning the amount of air exhausted equals the amount supplied—this prevents negative/positive air pressure that can pull in unfiltered outdoor air or push conditioned air out unnecessarily.

Every ducted HRV/ERV system has two primary duct runs:

• Supply Ducts: Carry fresh, pre-conditioned outdoor air from the HRV/ERV unit to living spaces (bedrooms, dens, family rooms).

• Exhaust Ducts: Pull stale, moist, or odorous air from “dirty” zones (bathrooms, kitchens, laundry rooms, basements) to the unit for energy recovery before being vented outside.

While HRVs and ERVs share this basic duct layout, their unique operating traits mean subtle differences in duct design, insulation, and placement—especially when it comes to moisture control and temperature retention.

Key Ducting Differences: HRVs vs. ERVs

The core distinction between HRV and ERV ducting boils down to moisture management and condensation risk, which directly impacts insulation needs, drain lines, and duct routing. Here’s how they stack up:

Ducting for HRVs (Heat Recovery Ventilators)

HRVs only transfer sensible heat (temperature) and do not move moisture between air streams, so they expel excess indoor humidity via exhaust air. This makes condensation a top concern in cold climates, as the exhaust air carrying moisture can cool rapidly in uninsulated ducts, leading to water buildup, mold growth, or even duct damage.

• Insulation Mandate: All HRV ductwork—both supply and exhaust—must be fully insulated, especially in unconditioned spaces (attics, crawlspaces, garages). Uninsulated ducts will lose recovered heat, driving up energy bills and creating condensation in cold weather.

• Drain Lines Required: Most ducted HRVs need a condensate drain line to carry away moisture that condenses in the heat exchanger core; this line must be routed to a floor drain, sump pump, or exterior exit to prevent water damage.

• Defrost Duct Considerations: In frigid climates, HRVs may need defrost cycles, and duct runs should be designed to avoid cold spots that worsen frost buildup in the core.

Ducting for ERVs (Energy Recovery Ventilators)

ERVs transfer both heat and moisture, balancing indoor humidity levels and drastically reducing condensation risk—this simplifies ducting requirements while boosting year-round comfort. Since moisture is exchanged instead of expelled, there’s far less risk of damp ductwork or condensate buildup.

• Insulation Still Critical (But Less Risky): Like HRVs, ERV ducts need full insulation to preserve energy recovery, but the reduced condensation risk means fewer worries about mold or water damage in unconditioned spaces.

• No Condensate Drain Needed: The permeable ERV core eliminates excess moisture buildup, so you can skip the drain line entirely—cutting down on installation complexity and maintenance.

• Flexible Routing: ERVs handle slightly more flexible duct routing than HRVs in cold climates, thanks to their frost-resistant design, though proper sizing and airflow still take priority.

Critical Ducting Rules for HRVs and ERVs (Non-Negotiable)

Whether you’re ducting an HRV or ERV, following these golden rules will ensure maximum airflow, minimal energy loss, and even air distribution throughout your home. Cutting corners here will leave you with stuffy rooms, high utility costs, and a ventilation system that fails to deliver on its promise.

1. Size Ductwork for Proper Airflow

Ducts that are too small create excessive static pressure, forcing the HRV/ERV fan to work harder, increasing noise, and reducing airflow. Ducts that are too large waste space and fail to maintain consistent air velocity. Always size ducts based on the unit’s CFM (cubic feet per minute) rating, local building codes, and the number of supply/exhaust vents. A licensed HVAC contractor can perform manual D calculations to get sizing perfect—never guess on duct diameter.

2. Minimize Bends, Elbows, and Obstructions

Every tight elbow, kink, or obstruction in ductwork adds resistance and cuts down on airflow. Use smooth, gradual bends (45-degree elbows over 90-degree elbows whenever possible) and avoid crimping flexible ducts. For rigid ductwork, seal joints with mastic sealant (not just tape) to prevent air leaks—leaks rob the system of efficiency and let unfiltered air seep in.

3. Separate Supply and Exhaust Ducts

Never mix supply and exhaust ducts or route them too close together—this can cause cross-contamination of stale and fresh air, or heat transfer between ducts before air reaches living spaces. Maintain a clear gap between the two duct runs, and route them through separate chases or joist bays to preserve performance.

4. Insulate All Ductwork in Unconditioned Spaces

Attics, crawlspaces, and garages are unheated/uncooled, so ductwork here loses massive amounts of recovered heat or cool air without insulation. Use foil-faced fiberglass insulation or insulated flexible ducts rated for ventilation systems to keep air temperatures consistent and prevent condensation. Even in mild climates, insulation boosts efficiency and protects against temperature swings.

5. Strategically Place Air Vents

Supply vents should go into occupied, dry spaces (bedrooms, living rooms) to deliver fresh air where you spend the most time. Exhaust vents belong in moisture/odor-prone areas (kitchens near stoves, bathrooms, laundry rooms) to pull out stale air at the source. Avoid placing vents near doors, windows, or HVAC registers that disrupt airflow, and don’t block vents with furniture or decor.

Common Ducting Mistakes to Avoid

Using Standard HVAC Ducts for Ventilation: HRV/ERV ductwork is designed for balanced ventilation, not forced air heating/cooling—repurposing old HVAC ducts often leads to poor airflow and leaks.

Skipping Insulation to Save Money: This is a false economy; uninsulated ducts can reduce HRV/ERV efficiency by 30% or more, leading to higher energy bills long-term.

Oversupplying or Underexhausting Air: Imbalanced airflow creates pressure issues, pulling in outdoor pollutants or pushing conditioned air out—always keep supply and exhaust CFM matched.

Using Low-Quality Sealing Materials: Duct tape deteriorates quickly; use mastic sealant or metal-backed tape for airtight, long-lasting joints.

Ducting HRVs vs. ERVs: Which Is Easier to Install?

For most homeowners and contractors, ERV ducting is simpler and more forgiving than HRV ducting. The lack of a condensate drain line eliminates the need to route plumbing, and lower condensation risk reduces stress about insulation gaps or cold duct spots. HRVs require extra planning for drain lines and defrost management, making them better suited for dry, cold climates where moisture control isn’t a top priority.

That said, both systems depend on flawless ductwork to perform—even the easiest-to-duct ERV will fail if installed with undersized, leaky, or uninsulated ducts.

Final Thoughts: Ducting Is the Foundation of a Great HRV/ERV System

Choosing between an HRV and ERV is only half the battle—proper ducting makes or breaks your ventilation investment. A well-designed, insulated, and sized duct system ensures your HRV or ERV delivers fresh, clean air evenly, cuts energy waste, and keeps your home comfortable in every season.

Before you start any installation, consult a licensed ventilation professional to assess your home’s layout, climate, and air quality needs. They’ll design a duct plan tailored to your unit, home size, and local conditions, so you can enjoy all the benefits of balanced energy recovery ventilation without the headaches of poor performance.

Don’t let subpar ducting undermine your HRV or ERV—prioritize quality installation, and your ventilation system will serve your home efficiently for years to come.