How to Compare HRV and ERV Efficiency
By Brett Sichello ·
Every high-performance home needs mechanical ventilation. Two public directories list tested units, and they answer different questions. This guide explains how to read them, and where a Passive House certified unit is worth its cost and where it is not required.
A heat recovery ventilator (HRV) or energy recovery ventilator (ERV) brings fresh air into the home and passes the heat in the outgoing air to the incoming air. An ERV also moves some moisture. A tight, well-insulated home depends on one, because the air it supplies is the only fresh air the house gets.
Two directories, two purposes
- The Passive House Institute component database lists units certified against strict criteria for heat recovery, electricity use, air leakage, balanced airflow, sound and frost protection. Certified Passive House projects use units from this list.
- The HVI directory (Home Ventilating Institute) lists units with ratings tested by designated laboratories using a common method. Because every unit is tested the same way, it is a fair way to compare one unit against another, including units that are also Passive House certified.
Open the Passive House database or the HVI directory as you read.
How to read the HVI table
- Net supply airflow. How much fresh air the unit delivers at a standard pressure. Size the unit to the home first, then compare.
- Sensible recovery efficiency (SRE) at 0°C. The share of heat recovered. Higher is better. Efficiency drops as airflow rises, so compare units at similar airflow.
- Net airflow at that SRE. The airflow at which the efficiency was measured.
- Power consumed. The electricity the fans use at that airflow. Lower is better, because the unit runs all day, every day.
- Efficacy. Airflow delivered per watt, where the directory gives it.
The table rates efficiency at 0°C. Performance in colder weather can differ, so check a unit's full rating before you choose. ERVs also tend to show lower sensible efficiency than HRVs, because they trade some of it for moisture recovery.
What the numbers look like
As of , the HVI directory lists 547 units, 374 ERVs and 173 HRVs. Their maximum rated SRE ranges from 59% to 94%, with a median of 77%, and 199 units are rated at 80% or higher.
The units below are a small sample of the better-performing HRVs rated at roughly 80 to 130 cfm, an airflow range used for a single-family home. Brands are not named, and you can find comparable units by filtering the directory yourself. The first entry is a Passive House certified HRV, shown for reference.
Passive House certified HRV (for reference)
- Sensible recovery efficiency at 0°C: 92%
- Net airflow at that rating: 97 cfm
- Power consumed: 30 W
Sample unit A (HRV)
- Sensible recovery efficiency at 0°C: 84%
- Net airflow at that rating: 95 cfm
- Power consumed: 43 W
Sample unit B (HRV)
- Sensible recovery efficiency at 0°C: 82%
- Net airflow at that rating: 85 cfm
- Power consumed: 34 W
Sample unit C (HRV)
- Sensible recovery efficiency at 0°C: 81%
- Net airflow at that rating: 81 cfm
- Power consumed: 97 W
Sample unit D (HRV)
- Sensible recovery efficiency at 0°C: 80%
- Net airflow at that rating: 85 cfm
- Power consumed: 98 W
The certified unit leads on both heat recovery and electricity use. The better standard units still recover more than 80% of the heat, which is a good result.
When a certified unit is not required
Passive House certified units and their duct systems are better, and that is clear in the numbers above. The ducting is more airtight and quieter than the flexible or rigid duct often used in standard installations, which can leak badly when it is not sealed well. If a project is going for certified Passive House, we use certified components.
Many homes are not going for certification. For those, a good HVI-listed unit with a well-designed, sealed and tested duct system delivers fresh air and good efficiency, and it can cost considerably less. The certified systems can cost much more once the unit, the proprietary ducting and fittings, and installation are all counted. It is one of the places where a project can save meaningful money without giving up a well-ventilated, efficient home.
What matters beyond the unit
- Duct layout and sealing. Short, smooth, sealed runs matter as much as the unit's rating.
- Balancing and commissioning. Supply and exhaust airflows need to be measured and balanced after installation.
- Filters and controls. Easy access to filters, and a boost setting for cooking and bathrooms.
- Where air enters and leaves. Intakes and exhausts placed well away from each other, from dryer and range exhausts, and from sources of smoke.
For how ventilation fits with the rest of a high-performance home, see Six Enemies of Heat Loss in Homes and Designing for Wildfire Smoke and Extreme Heat. To talk about your own project, see the FAQ or get in touch.