Your home’s indoor air quality (IAQ) is vital to living a comfortable, healthy life. Effective ventilation helps improve indoor air quality as it reduces levels of pollution and moisture that may directly or indirectly have adverse health effects.
As homes are being built to be more airtight and energy efficient, HRVs have been increasingly important to keeping indoor air fresh:
- The Ontario Building Code made them mandatory in all new homes built in Ontario since January 1, 2017.
- The British Columbia Building Code made changes in 2014 that required there to be a ventilation system that ran continuously, making HRVs all but required.
- The 2010 National Building Code of Canada requires there to be a mechanical ventilation device or considerable natural ventilation in order to provide fresh air during the non-heating-season.
- What is an HRV?
- How does an HRV work?
- HRV vs ERV
- What should the settings be?
- Do I need an HRV?
- How to maintain an HRV?
- How much does it cost?
- How to choose
What is a heat recovery ventilator (HRV) system?
A heat recovery ventilator is a home ventilation system that improves indoor air quality by bringing fresh air into your home from outside and blowing stale air inside your home outside in an energy efficient way. It saves energy in the winter by transferring some of the heat in the outgoing exhaust air into the cold incoming air, reducing the demand on your furnace.
An HRV can recover (save) 65% to 85% or more of the heat energy from the outgoing air which directly reduces your energy bills.
HRVs are an addition to an existing HVAC system and do not require the furnace or air conditioner to function. They are sometimes linked via ductwork to specific rooms in a home, but these days are commonly connected to an existing central heating system. They are not a dehumidifier, but can also be used to regulate relative humidity (RH) in a home in the winter months.
They help improve indoor air quality by filtering the incoming air to trap dust, pollen and insects and by expelling unwanted or harmful pollutants such as gasses: carbon dioxide (CO2), carbon monoxide (CO) and radon, volatile organic compounds (VOCs), smoke and odours.
How does an HRV work?
An HRV is a mechanical ventilation device that contains a fan, heat transfer core made out of aluminum or plastic and two replaceable reusable filters. It is connected to 4 ducts:
- Fresh air from outside to HRV
- Warm air supply to home from HRV
- Stale air from home to HRV
- Air exhaust to outside from HRV
After passing through their filters, the incoming and outgoing air streams pass through the many narrow airtight channels inside the heat transfer core (central diamond pictured above). The air streams do not mix/touch inside the core. The channels alternate between incoming and outgoing, so every other channel is dedicated to a specific air stream.
Each stream flows through its set of channels side-by-side the other stream. The thin dividing walls between the channels allow heat to transfer easily.
In the winter, the core transfers heat from the warm, stale air from the house to the cold fresh air coming from outside – pre-warming up the air sent into your home’s ductwork.
In the summer, the process works in reverse. The air-conditioned stale air from the house cools the warm, fresh air coming from outside – cooling down the air sent into your home’s ductwork.
This process reduces the energy used by your home’s heating (cooling) systems to raise (lower) the outside air up (down) to the temperature set on your home’s thermostat. The annual energy savings of an HRV used in a home with a gas furnace and central AC range from $50 in Vancouver to $180 in Winnipeg, when compared to a less airtight house that uses exhaust fans intermittently. The colder the region, the higher the savings.
The HRV is usually connected to additional on/off switches or timers in the bathrooms and/or the kitchen that may be used to manually turn on the HRV system or set it on high for a period of time in order to remove excessive moisture produced during a shower or while cooking.
Heat Recovery Ventilator (HRV) vs Energy Recovery Ventilator (ERV)
HRVs and ERVs are very similar in construction and operation. They both bring in and filter fresh air, distribute it through the home, exhaust interior air and recover heat energy. The main difference is that while an HRV’s core can exchange heat, an ERV’s core can exchange both heat and moisture between the air streams.
The core is made of a permeable material or desiccant (a solid that absorbs water eg. silica gel) wheels that allows moisture to move from the higher humidity stream to the one with lower humidity, equalizing the humidity of the incoming air. An ERV can transfer 32% to 68% or more of the moisture from the outgoing air.
ERVs in winter
ERVs keep more humidity in your house than an HRV which make them the better choice if your house already has low humidity in the winter months. A portion of the heat and humidity is transferred from the outgoing air to the fresh incoming air, which prevents the humidity from decreasing too much. This reduces the need and costs of running a separate humidifier.
ERVs in summer
Moist air is harder to cool, so an ERV will help reduce the demand on your air conditioner by transferring some of the humidity from incoming air to outgoing air and allow you bring fresh air into your home regularly and automatically. However, a separate dehumidifier is often required. They are most commonly found in hot and humid climates such as the southern US (Florida, Texas, Louisiana).
How to choose between HRV and ERV
The size of HRV necessary for your home depends on:
|Number of occupants||Many||Few|
|Regional climate||Mild, humid winters||Cold, dry winters|
Here is a zone map of Canada and the US from a manufacturer’s installation manual for determining the best unit type and defrost setting:
What should the settings be?
Every home is different (size, age, occupancy, HRV type, etc.) so the following is a general guide:
On our control panel the manufacturer’s instructions state:
During fall, winter and spring, set the dial according to the desired maximum indoor humidity level. During summer set the dial to the off position.
While some sources suggest that you should run your HRV continuously on the minimum/lowest setting, in winter, if your home already has low humidity, doing so may bring in too much cold, dry air and cause overdrying. This may cause your furnace to run longer and more often than necessary to keep your home warm. It does not take much -20°C air intake to reduce the indoor relative humidity to a reasonable level.
In summer, especially when air conditioning has been running, the air outside is much more humid and running the HRV will bring this humidity into your home and remove cool, dry air. This is the opposite of what it’s designed to do, so the best approach is to set it to the highest percentage or shut it off. To avoid excessive indoor humidity in the summer (if the process of air conditioning isn’t sufficient or available), it is recommended to use an ERV or separate dehumidifier.
Recommended maximum humidity levels
Your home’s humidity affects the quality and comfort level of your indoor air and should not be too humid or too dry.
The biggest sources of humidity in a home are breathing, baths/showers, cooking, dish washing and indoor gardens.
Health Canada recommends keeping the humidity above 30% in the winter and keeping it below 55% in the summer, so it should be between those levels in order to keep the following health effects minimized:
In winter, set the dehumidistat just low enough (25% to 40%) to prevent condensation on windows and other surfaces that may allow for mould and mildew growth and reduced IAQ.
In summer, the best approach is to set it to the highest percentage or shut it off.
|Outdoor Temperature (°C)||Practical Humidity Level|
|Summer||100% or off|
If air is too dry
Lack of humidity (overdrying) can cause dry, itchy skin, sore throats, static electricity and cause caulking to crack, baseboards to warp, and damage to artwork and woodwork.
If the air in your home is too dry:
- Increase the maximum humidity level on the dehumidistat or turn it off (prevent overventilation)
- Seal and weather strip to reduce leakage
- Replace windows and/or doors
- Use a humidifier
If air is too humid
High humidity (underdrying) can cause window condensation and mould and mildew growth.
If the air in your home is too humid:
- Reduce the maximum humidity level on the dehumidistat or switch it to high
- Don’t hang wet clothes to dry indoors
- Open the windows or run an exhaust fan while in the bath/shower and for 15 minutes after
- Ensure your dryer’s exhaust is properly vented to outside
- Use a dehumidifier
Do I need an HRV?
Older homes have cracks, gaps and broken seals around windows and doors which provide some natural ventilation, but make it harder to control the temperature, air quality and humidity and lead to excessive energy costs. Opening windows can also help with ventilation, but can also make it harder to regulate humidity and keep energy costs down.
Conventional (80% efficient) furnaces draw air from the area immediately surrounding them and the negative pressure will pull air from the path of least resistance such as a fresh air intake, or if that is blocked or non-existent, from unconditioned spaces such as attics, dryer vents, and leaks around windows and doors which reduces the quality of air in your home and make your furnace less efficient.
Newer homes are designed to be airtight to increase energy efficiency and reduce heating and cooling bills, but this can cause indoor air to become stale due to re-circulation.
High efficiency (90% efficient) furnace models draw air directly from outside through a dedicated pipe that runs directly from an outside vent to the furnace’s sealed combustion chamber. No air is drawn from recycled from inside your home and a fresh air intake is not necessary.
While most are present in small amounts inside a home, some are dangerous to human health. Short-term exposure to high levels can cause breathing issues, headaches, asthma and ear, nose and throat irritation. Chronic exposure to low levels can have long-term health effects, though researching their impact is difficult since the symptoms are slow to develop.
Signs your home has poor ventilation
- Lingering odours from pets, cooking or other activities
- Condensation on windows
- House feels stuffy
How to maintain an HRV?
An HRV should be cleaned once a year at the end of summer and the filters should be cleaned every 3 months.
- Turn off the HRV by unplugging it
- Pull the tabs at the bottom down and back
- Open the front panel and slide it to the side to remove it for easy access
- Slide the core (black diamond) straight toward you to remove it
- Remove the filters next to the stale air from home and fresh air from outside ducts
- Vacuum the inside of the unit with a shop vac and/or wipe out the debris with a warm damp washcloth.
- Clean the core by soaking it in warm water and dishsoap and by pouring water through the channels (best done in the bathtub or a large bucket) or by rinsing it outside with a hose.
- Gently vacuum and/or wash the filters in warm water and dishsoap (or replace them)
- Let everything dry completely before reinstalling
- Check outdoor intake and exhaust hoods for debris or obstructions
Here is a straightforward step by step video guide:
How much does an HRV or ERV system cost?
According to the price list of GasExperts.ca, the cost of a residential HRV air exchanger unit ranges from $750 to $2500 with an average of $1200. ERVs are slightly more expensive and range from $700 to $2900 and an average of $1350.
Cost per month to run
The cost to run an Energy Star certified HRV on the low setting 24/7 ranges from $2.76 to $9.22 per month based on power consumption of 30 to 90 watts and electricity prices of 12.8 to 14.2 cents/kwh.
|30 watts||90 watts|
The cost of a basic reusable (washable) foam HRV filter ranges from $30 to $60, while a disposable HEPA filter ranges from $25 to $90. I called Venmar customer service and they confirmed that all but one of their HRVs use reusable foam filters. The G2400H has MERV 6 grade filters with optional HEPA filtration.
While the purpose of air exchanger is to move air quickly and efficiently and a high MERV filter would slow air flow, it seems strange that there wouldn’t be any replaceable filter options available. If my furnace or AC is on, the air passes through a MERV 8 filter and is rated to remove mold spores, hair spray and dust.
When pulling fresh air from the outside, one would think the air would be given the same level of care. However, it is instead passed through an unrated foam filter that seems to catch bugs and dust, but what about pollen, bacteria and pollutants? Selling higher quality replaceable filters would also enable them to sell more filters and likely for higher prices.
Installation and maintenance cost
The cost to have a new air exchanger installed based on pricing collected for the Greater Toronto Area ranges from $1500 to $3250, which includes $600 for labour and $150 for additional materials such as ducting, tape and intake and exhaust hoods.
|New air exchanger installation||$598 + $165 accessories|
|Air exchanger replacement||$348|
|Air exchanger maintenance||$96|
How to choose an air exchanger
Look for a model that has been certified by the Candian Standards Association (CSA), has had its performance certified by the Home Ventilation Institute (HVI) and meets the energy efficiency requirements of Energy Star. To quality, they must provide a sensible heat-recovery efficiency (SRE) rate of at least 65% at 0°C and 60% at -25°C.
All HRVs and ERVs installed in Canada must be listed by the Home Ventilating Institute (HVI).
What size HRV do I need? How much fresh air is enough?
In Canada, the ventilation capacity is prescribed according to the type and number of rooms to take into account the activity of the occupants rather than the dimension of the living space.
The necessary ventilation rate depends on the codes and standards that apply to your area. The following is an example calculation for reference only that adheres to CSA F326‐M91, Residential Mechanical Ventilation Systems which is referenced by the National Building Code and most provincial codes.
The example above is for a 3 bedroom, 2 bathroom home. The system is sized based on the larger of the calculated values for supply (60 L/s) and exhaust (50 L/s). In this case 60 L/s would be required minimum rate in order to meet the standard. The air exchanger is then selected so that the minimum rate is only approximately 60% of its maximum airflow capacity to account for temporary increases in home occupancy and usage.
The standard parts warranty for HRVs and ERVs is 5 years, while the core warranties range from 5 to 10 years for ERVs and limited lifetime for HRVs.
What to read next
- Ventilation and the indoor environment – Government of Canada
- Ventilation & air quality – Manitoba Hydro
- Improve indoor air quality – Government of Canada
- How to Maintain a Heat Recovery Ventilator – CMHC
- Heat Recovery Ventilators – Natural Resources Canada
Over to you
We’re interested to know – do you have an HRV or ERV in your home? How much did it cost to install? How do you use it and do you find it does a good job?