Heat Recovery Ventilation (HRV) systems are important for maintaining a healthy indoor air environment by continuously replacing dirty indoor air with clean outdoor air while conserving energy. The HRV system has a central core heat exchanger that transfers heat from stale indoor air as it leaves and replaces it with clean air, keeping you comfortable while properly ventilating your home.
If there is any malfunction with any of the HRV system components, you will start to see changes to the environment inside your home; you may experience an increase in the humidity level and/or the amount of energy used to heat or cool your home, along with a decrease in the quality of the indoor air. By identifying the signs of a malfunctioning HRV, you can get the HRV system working at peak performance levels.
Water Build Up
Water can build up inside the unit due to a lack of airflow. One of the functions of an HRV is to take damp, stale air from inside a home and replace it with dry outdoor air. When the condensate drain (the pipe that carries moisture away) becomes clogged or frozen, the HRV cannot remove enough moisture from the home. If moisture builds up inside, it may promote mould growth and/or damage windows and drywall.
Lingering Odours
Stale air with lingering odours. When an HRV functions properly, cooking odours or bathroom odours should leave the area quickly once removed. If a smell persists in the house for an extended time or the house feels “stuffy,” there is probably a blockage in the airflow into the HRV. This blockage is often caused by a dirty filter (the filter that keeps dust and other contaminants from entering the HRV) or by a blockage in the outdoor intake hoods (the hoods on the outside of the HRV that allow air to enter). Low airflow into the HRV allows carbon dioxide (CO2) levels to build up, which can cause people to feel fatigued and have difficulty sleeping.
Unusual Mechanical Noises
A properly working HRV shouldhum quietly with a low level of noise. Loud grinding, squealing, and rattling indicate a problem with the machine’s mechanical parts, such as worn motor bearings or a loose fan blower. Rattling of the unit usually indicates it has shifted from the mounting straps due to inadequate support. The unit will whistle when high pressure builds within the unit, indicating that the motors are working hard to move air because something is blocking the airflow.
Ice Accumulation (Freezing)
In colder weather, the heat-exchange core may become completely covered in ice if the HRV’s defrost cycle malfunctions. You may see water leaking from under the HRV’s case or hear the fans trying to move air. This freezing of the core is often the result of the dampers that activate the defrost cycle becoming stuck in the closed position or of the outdoor temperature sensor failing. When the heat-exchange core is frozen, it completely stops airflow through the HRV, so your HRV will not provide ventilation to your home when it is needed most.
High Energy Bills
An unbalanced HRV puts a substantial additional load on your heating system (furnace/heat pump) to deliver the same heat output. An HRV is considered to be ‘over-ventilating’ when it draws too much cold air into the house without adequately returning heat; therefore, the heating system will run continuously to offset the increased air exchange. The intake and exhaust airflows will be balanced using a manometer; if the two measurements are out of balance, even by a small amount, the pressure difference created will pull cold air through electrical outlets and door frames.
Visible Debris or Mould Near Vents
If you have dark or dusty spots above the ceiling supply grilles, it’s likely that the filtration system in the HRV has either not been cleaned (by-passed) or reached its capacity (saturated). Polluted outdoor air and dirty indoor air can now easily circulate through the ducting system. To prevent the system from contributing to the existing indoor pollution, it is recommended that the internal filters and the heat recovery core be cleaned every 6 months.
Windows Fog Up or Develop Frost in Winter
Windows are susceptible to fogging or frost in winter due to condensation; this is a common indicator of poor ventilation. When warm air with moisture encounters the cold surface of the window, condensation in the form of water droplets or frosting occurs. Condensation on windows is often blamed on poor insulation; however, it is most often due to a lack of airflow and/or a blocked exhaust.
If the condensation on the window persists for an extended period of time, it can result in the following issues:
- Development of mould around window frames
- Damage to drywall and/or wood trim
- Shortened lifespan for the window itself
A properly adjusted HRV system will remove excess moisture from the home before it becomes visible as condensation.
When to Call a Professional
Although many homeowners can perform regular maintenance, such as periodic filter changes and cleaning their HRV units, some tasks (such as checking for proper airflow) require tools and equipment available only to a professional service provider. The HRV is an extremely delicate instrument; if the airflow isn’t perfectly balanced, it can shift from an asset that lowers your heating costs to an energy-consuming liability that could also damage your house.
- Total System Performance Assessment
- Using calibrated instruments, measure and confirm the air at each supply and exhaust grille on both sides of the HRV.
- Calculate and compare the HRV to the system’s original design specifications.
- Inspect all ductwork for signs of failure, including crushed/collapsed areas, leaks, and loose connections, and confirm that each area of the ducts has proper insulation.
- Check that the HRV is appropriately incorporated into the existing heating and cooling systems.
- Precision Airflow Balancing
- The balance of intake and exhaust airflow is determined using digital manometers.
- If the system is not balanced, it may create pressure, causing cold drafts to blow into your house, or moisture could be trapped in your walls.
- Deep Cleaning
In addition to filter rinsing, heat recovery cores and fans are cleaned during HVAC maintenance.
- Electrical Diagnostics
Expert electrical diagnostics performed by HVAC technicians on HVAC Equipment (motors and Capacitors, as well as Thermally Activated Electronic Control Equipment, like a Control Board) and electrical wiring Connections enable the technician to pinpoint the exact location of the electrical failure, thus helping to avoid the cost of replacing the entire motor due to a small electrical issue early on.
- Ductwork Integrity Audit
- A ductwork integrity audit (including insulation and vapour barrier inspections) is performed by skilled technicians to verify that the ductwork is free of air leaks.
- If your ductwork has air leaks, your system draws in polluted outdoor air from areas like attics and crawlspaces instead of drawing only clean, fresh air.
- Control System Development
- Create an HRV program to provide intermittent or demand-controlled ventilation, based on your home’s occupancy patterns.
- Set up responsive humidity and CO2 levels for automatic, responsive ventilation (when available).
- Integrate HRV controls with other home systems to create a seamless, intelligent operation.
- Proactive Maintenance and Training
- Conduct an in-depth cleaning of the HRV unit, HRV core and any other accessible ducts within the HVAC system.
- Provide guidance for the homeowner on routine maintenance tasks and schedules.
- Record all service findings along with all adjustments, repairs and recommendations for future maintenance.
Protect Your Indoor Air Quality
To restore comfort, air quality and energy efficiency, when the do-it-yourself approach does not fix the HRV issues, it is time to contact the professionals. At Horizon Heating, we offer comprehensive HRV services to restore your system to peak efficiency, delivering superior indoor air quality and energy savings. Our certified technicians are trained to follow a comprehensive diagnostic and repair procedure to identify and resolve all types of ventilation problems. Contact Horizon Heating (403) 274-0790 for HVAC services, expert installation, and advice on HRV units.