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3. Operating Your HRV

Operating Your HRV

Once an HRV is installed, balanced and functioning, its ongoing operation is relatively simple. By following these general guidelines and paying close attention to the manufacturer's and installer's instructions, you can help ensure the safe and reliable performance of your HRV.

Controls

First, become familiar with the HRV's controls, which allow you to adjust the rate of air exchange and, to some degree, the humidity level in your home. Depending on the installation and the HRV model, operating controls may be located on the HRV itself and/or in the kitchen, laundry room, bathroom or hallway. Pollutant sensors may be installed in other rooms of the house. Typically, the main HRV control is placed adjacent to the home's main thermostat.

The operating controls may include the following functions depending on the installation and the HRV model:

  • high-speed and low-speed controls;
  • a circulation mode setting, which circulates air inside the home but does not exchange indoor and outdoor air;
  • a dehumidistat that will trigger the HRV into high-speed operation when the humidity level in your home reaches a pre-set level;
  • a timer, which can be set to run the HRV at high speed for specified intervals;
  • an intermittent exchange mode setting that automatically turns on the HRV at low speed for specified intervals;
  • pollutant sensors that increase the ventilation rate when pollutant levels in the home rise; and
  • a maintenance light, which comes on automatically when the filters, and possibly other components, need to be cleaned or serviced.

Low-Speed Operation

To ensure the removal of indoor pollutants and the supply of fresh outdoor air, an HRV should be operated on low speed continuously year-round, especially in tight homes and homes with average indoor pollutant levels.

Under most circumstances, low-speed operation will meet your ventilation needs (for exceptions, see “High-Speed Operation” and be more effective than intermittent high-speed operation. Operating in intermittent exchange mode may be appropriate when pollutant sources are low, the house is not overly tight, or the occupants are away from the home for extended periods.

If you turn off the HRV, remember to make other provisions for ventilation, such as opening windows.

High-Speed Operation

Under certain conditions, the ventilation rate in your home may need to be increased from low-speed operation. Depending on the installation, a high-speed cycle may be triggered manually or by a timer, dehumidistat or other controls.

High-speed operation is often needed in the kitchen and bathrooms. It also may be required when

  • you are using paints, solvents, cleaning products and other household chemicals;
  • the house air seems stale, contains odours or is too humid; and
  • there are many people in the house, such as during a party.

Operating the ventilation system on high speed will also help improve air quality when people smoke in the house. Tobacco smoke is one of the most noticeable and harmful indoor air pollutants. If possible, smoking should be confined to rooms that are exhausted directly to the outdoors, either through the HRV or through a separate exhaust system (such as a kitchen fan).

Frequent or even continuous high-speed operation may be desirable during the first year after a house is built, in order to exhaust the moisture and pollutants being released by new building materials.

An HRV is not an air cleaner and may not deal effectively with extraordinary sources of indoor air pollutants (e.g., strong-smelling glues), particularly if the pollutants are generated in a room that is not exhausted directly to the HRV. In such cases, occupants should reduce the activities that are generating the pollutants or install a dedicated exhaust system.

Considerations for Heating Season Operation

Most HRVs feature an automatic defrost mode that activates when the temperature of the incoming fresh outdoor air is below -5°C. Some type of defrosting mechanism is required in cold climates because, as the heat is extracted from the home's outgoing moist air (to warm the incoming fresh air), the temperature of the outgoing air drops to the point where moisture/frost can form on the surfaces of the heat-exchange core. A build-up of frost can block airflow through the HRV.

One type of defrost mechanism uses dampers to temporarily block the incoming fresh air stream and allow warm air from the house to circulate through the HRV, where it melts any frost that has accumulated. The HRV returns to normal operation after this automatic defrost cycle. As the outdoor air gets colder during the winter, this cycle increases in duration.

Another approach is to use an electric resistance heater to preheat the fresh air before it enters the core. With this strategy, defrosting is not required since the preheating prevents frost from forming.

To help minimize condensation on cold surfaces, such as windows, during the heating season, adjust your HRV's dehumidistat accordingly. Keep in mind that you do not want the household air to be too dry, as this can cause static electricity and dry, scratchy throats. If the air in your home is too dry during the heating season and you have attributed this to the HRV's operation, refer to the HRV Troubleshooting Guide.

Considerations for Non-Heating Season Operation

The best strategy is to operate your HRV continuously year-round, even during the non-heating season. Except for adjusting the dehumidistat setting, operation should be essentially the same as during the heating season.

You may find that operating the HRV keeps the home cooler and quieter than opening windows for ventilation. Keeping windows closed also provides better security and reduces the amount of pollen and dust entering the home.

Some modern HRVs give you the option to turn off the low-speed setting. Even with this setting turned off, the HRV can still be set at high speed to remove excess moisture and odours from the kitchen and bathrooms. This is useful in the summer, when, with open windows thoughout the house, mechanical ventilation may be unnecessary.

By removing some of the heat from the incoming air, most HRVs will reduce the load on the air conditioner and save you money.

Considerations for All Seasons

Keep contaminants away from the fresh air intake when your HRV is operating. For example, avoid putting trash next to the HRV intake, do not use pesticides and herbicides nearby, and keep your barbecue downwind. If you must temporarily generate pollutants near the HRV intake, turn the HRV off until the activity is complete.

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Source: Natural Resources Canada (NRCan) - Office of Energy Efficiency

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