Heat Recovery Ventilator (HRV)
Reduced Energy Consumption
- Reduces ventilation costs by using heat in outgoing exhaust air to warm incoming fresh air in the winter.
Improved Indoor Environment
- Ensures delivery, distribution and circulation of fresh outdoor air throughout the house.
- Controls indoor air humidity levels to prevent moisture problems such as condensation on windows and mold growth.
- Helps control odours and humidity levels in bathrooms and kitchens.
- Dilutes indoor air contaminants.
- Provides better comfort by warming incoming ventilation air.
- Filters incoming air.
- Energy Recovery Ventilators (ERV) can also recover moisture from air to help prevent over-drying of home in the winter.
Reduced Environmental Impact
- Reduces energy consumption-related green house gas emissions due to heat recovery that offsets energy otherwise used to heat ventilation air.
- HRVs are mechanical devices that exchange stale indoor air with fresh outdoor air (see Figure 1). Heat is transferred from the outgoing air to the incoming air by passing the two air streams through a heat-exchange core. The two air streams are kept separated, and only the heat is transferred to the incoming air, which is then circulated throughout the house. In most cases, fresh air is delivered to bedrooms and the living room, while stale air is removed from bathrooms, laundry rooms, and the kitchen.
- HRVs provide energy efficient mechanical ventilation, especially in energy efficient new houses where uncontrolled airflow is minimized. In a well-sealed house, an HRV is much more effective at recovering a large percentage of the heat that would otherwise be lost by means of uncontrolled airflow through the house. HRVs provide ventilation for existing housing as well, especially when energy efficient measures such as air sealing and insulation upgrades have made the building envelope tighter, or when the house is subject to condensation or other indoor air quality problems because there is poor or no air flow in the house.
- HRVs have multi-speed settings to deal with varying ventilation needs. Automatic controls are available as well to modulate the operation of the HRV based on time and indoor humidity level.
Figure 1 — Heat Recovery Ventilator Schematic
(Source: OEE, NRCan)
The ducts bringing fresh air from the outdoors and stale air from inside the home cross by each other in the heat exchange core of the Heat Recovery Ventilator and the heat from one flow of air is transferred to the other. The fresh air is directed into the house while the stale air is exhausted outside.
HRV Schematic — from Heat Recovery Ventilators published by OEE — permission received to use image. Source: "Components of a ventilation system using an HRV", Natural Resources Canada, 2012. Reproduced with the permission of the Minister of Natural Resources Canada, 2014.
Energy Recovery Ventilators
ERVstransfer heat and moisture energy from the air which makes them potentially more efficient than an HRV, depending on humidity levels, climate type, and the house. ERVs are best suited to houses that need humidification in the winter and cooling in the summer. ERVs are not suitable when ventilation is required to address high indoor moisture conditions.
Figure 2 — Common Types of Heat Recovery Ventilators
In the plate heat exchanger, supply fan pushes the fresh air from outdoors through a row of plates set at a 45 degree angle to the base of the Heat Recovery Ventilator while the exhaust fan draws the stale air from indoors through the row of plates. The exchange of the heat in one air flow to the other takes place as the air flows pass through the row of plates.
In the wheel heat exchanger, the transfer of the heat takes place in a heat wheel set perpendicular to the base of the Heat Recovery Ventilator. The supply fan and the exhaust fan move the fresh air from outdoors and the stale air from indoors through the heat wheel.
- HRV systems should be designed and installed by qualified personnel (certified by the Heating, Refrigeration, Air Conditioning Institute of Canada, HRAI, or other training organization) in accordance with current building codes and standards.
- HRVs in today’s market vary widely in their ‘sensible efficiency’ ratings. Look for units with lower energy usage and high sensible efficiency in the heating season, preferably choosing from those with an ENERGY STAR® rating.
- Specification sheets showing the energy usage and efficiency of any unit are typically available from manufacturers’ websites.
- An HRV can supply fresh air in several ways:
- Directly ducted to each room, and exhaust air from kitchens and bathrooms via a dedicated ductwork system.
- Indirectly to the house through the forced air heating system while directly ventilating bathrooms and kitchens.
- Connected to an existing forced air heating system only to provide general indoor-outdoor air exchange — a common approach for existing houses with this type of heat distribution system.
- To avoid cross-contamination problems, the outdoor fresh air intake and exhaust outlet must be carefully located with respect to dryer vents, vents and air intakes serving space or water heating devices, and windows and doors. The intake and outlet must be at certain heights above grade to avoid snow build-up, and they cannot be located under decks, in garages or in attics.
- HRVs cannot be connected to range hoods, cooktops or clothes dryers.
- The supply and exhaust airflows must be measured and balanced to ensure the HRV does not cause house depressurization or pressurization problems. This should be carried out when the HRV is first installed. Airflows can become unbalanced over time and therefore should be checked regularly by a qualified contractor in accordance with the manufacturer’s instructions.
- HRVs require minimal annual maintenance to ensure energy efficient and safe operation. At the beginning of each heating season, clean the filter and heat recovery core, inspect and clear the screens in the outdoor intake and outlet hoods. Check manufacturer’s literature for requirements.
What Does it Save?
Replacing air exchangers or whole-house exhaust systems that do not have heat recovery with a high-efficiency, ENERGY STAR® HRV can reduce ventilation energy requirements and associated costs by 50 to 70%.
Here is an example of how much a family of four living in a typical 1970’s 2-storey house with a full basement and three bedrooms could save in ventilation costs by replacing an air exchanger with a high efficiency ENERGY STAR rated HRV. A typical air exchanger for a house of this size, providing ventilation to the whole house would use 960 to 1080 kWh a year. Replacing it with a high-efficiency HRV that uses 340 to 400 kWh a year results in a 65% reduction in energy costs associated with ventilation.
HRV Annual Energy Cost Saving
|Annual Ventilation Energy Costs Before Retrofit
|Annual Ventilation Energy Costs After Retrofit
Figure 3 — Riverdale EQuilibrium™ (Net Zero) Demonstration Project in Edmonton — Heat Recovery Ventilator
Figure 4 — HRV Control
The information contained in this publication represents current research results available to CMHC. Readers are advised to evaluate the information, materials and techniques cautiously for themselves and to consult appropriate professional resources to determine whether information, materials and techniques are suitable in their case. The text is intended as general information only and project and site-specific factors of climate, cost, aesthetics, practicality, utility and compliance with applicable building codes and standards must be taken into consideration. A number of assumptions were applied with respect to fuel prices, water rates, costs of materials, equipment and labour, planning horizons, etc. Actual reductions in energy consumption and fuel savings will vary. Any reliance or action taken based on the information, materials and techniques described are the responsibility of the user. CMHC accepts no responsibility for consequences arising from the reader’s use of the information, materials and techniques herein.
Last revised: 2013