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The Difference Between Heat Recovery Ventilators (HRV) and Energy Recovery Ventilators (ERV)

As homes become “tighter”, we are seeing more recovery ventilators installed either with the furnace / AC air handler or as stand alone units. Many systems include the kitchen and bathrooms to provide fresh air. Many homebuyers see these units in the mechanical room or basement, but do not actually know what they do or if they are installed properly. I also see real estate listings incorrect when describing the installed equipment. We will detail the difference between the three units and how you should advise your client.

Air Exchanger – Takes stale inside air out and replaces it with outside fresh air. This is the least effective way to properly condition and ventilate the house. It is however the most inexpensive and better than not having any air exchanges at all especially in well insulated, sealed houses.

Heat Recovery Ventilator (HRV) – Most commonly used for heating. Outgoing stale air and incoming fresh air pass each other in a heat exchanger. In heating mode, the outgoing warm air heats the incoming cold air. In cooling mode, the incoming hot air is pre-cooled by the outgoing air. The incoming and outgoing air are kept separate to prevent the inside air from being contaminated. Condensation drains are installed.

Energy (Enthalpy) Recovery Ventilator (ERV) –   Is most commonly recommended for cooling. ERV’s not only recover heat but also recover moisture. The vapor permeable membrane between the exhaust and intake sides of the heat exchanger is different. An aluminum or polypropylene one is found on an HRV. A special fabric material that will allow vapor to pass through is installed on an ERV. Humidity is normally kept below 50%. ERV’s are usually about 10% less efficient than HRV’s.

Here is what a home inspector should look for and how to properly advise your client:

  • Ensure the condensate drain discharge drains in accordance with accepted standards.
  • Newer tight homes need mechanical ventilation from the outside to provide oxygen, to remove contaminants, & to remove excess humidity.
  • Many new building materials, unlike the past produce toxins and off-gas for quite some time after installation; possibly years.
  • An average home with average leakage would leak out the entire volume of air and be replaced 3-4 times per day. This would be considered insufficient, not to mention the quality of the incoming air, which is “filtered” through the building envelope. Any spores, VOC’s, or Mold trapped inside the walls can be drawn into the living space.
  • If your clients home is humid during the winter months (above 60% RH), an HRV is the better choice. If your client’s house is too dry in the winter, then an ERV is a better choice. It will retain enough humidity, but not enough to accommodate mold growth. It will also eliminate the need for a humidifier and all of its problems.
  • In the summer months, an HRV will usually increase the humidity level inside your home. An ERV may be a better choice in hot humid areas.
    An ERV should lower the load on the air conditioner

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