Leonard Splaine What is the difference between an ERV and HRV system?

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All homes need ventilation, whether natural or mechanical with an ERV or HRV system. Buildings and houses are no longer constructed leaking heat and moist air the way they used to be; we now build them as airtight as we can, especially Passive House or LEED certified homes. This makes mechanical ventilation essential in these high performance home by installing either HRV or ERV Ventilation Exchanger Systems.

Adding a ventilation system to your home can be beneficial for a number of reasons: It keeps the air in your home fresh, it can diminish allergens or pollutants in the air, and it can help retain relative humidity while preventing too much moisture to remain in your home.

What is the difference between an ERV and an HRV?

Heat Recovery Ventilation (HRV) is a system that uses the heat in stale exhaust air to preheat incoming fresh air. This reduces the energy required to bring outside air up to ambient room temperature so saves money on heating bills.

Similar to the human breathing system as mentioned above, this exchange of air is performed in a single area of the home, the lung of your home, your HRV ventilator core.

Note that outgoing stale air and incoming fresh air never mix in the heat recovery process; they simply pass in separate channels in the ventilator core, the heat exchanger, allowing an exchange of heat through conduction.

The ‘efficiency rate’ of an HRV unit determines how much energy will be saved by using that particular device. Although it requires the operation of a fan on a continual basis, the energy recovered from the inside air is many times that of the energy required for the fan. Worth noting that in our experience it’s worth spending a little extra on a quality brand of HRV, because the fan is what generally breaks first, and it’s what you hear (or not), and the established brands have worked extensively on R & D to use energy-efficient silent fans that last longer. When the fan does break, these established brands of HRV’s are the ones who generally have good after sales service and stock replacement parts for a large number of years.

Typical efficiencies range from 55% to 75%, but some extremely efficient models are rated as high as 93% efficiency. At present, these latter units are significantly more expensive and only generally available from Europe, though as HRV units are becoming the norm, higher efficiency ones can be found in the US & Canada.  Even so, when you factor the value of energy savings over the unit’s full life cycle, shipping these relatively costly units across the ocean can still make it a financially and ecologically sound investment.

Energy (or Enthalpy) Recovery Ventilation (ERV) goes a little further than the HRV units, as this type of system also captures some of the humidity in the air to keep it on the same side of the thermal envelope that it came from.

So in cold winter climates, an ERV system transfers the humidity from the air being extracted to the incoming fresh (and dry) air to help keep the ambient internal humidity level at a reasonable value (between 40 and 60%) at all times.

In summer, the humidity transfer in an ERV reverses and the humidity in outside air is removed before it is injected into the home. This saves energy by reducing the load on air conditioning systems and/or dehumidifier. A high efficiency of humidity transfer would be around 70% but this value depends on the actual humidity on either side of the envelope.

One important note is that whatever you choose for your needs between an ERV & HRV, there will always be a power on/off switch. If your system is too noisy, you will likely turn it off for long periods of time even if you really need it. Choose a quiet ERV or HRV system and ensuring that it is installed properly to avoid the temptation of turning off a piece of equipment that represents both a financial and health investment.

ERV or HRV – Which to choose?

The best option between an HRV and an ERV depends on your climate and specific needs. If your house is too humid in winter (above 60% RH) then an HRV is the better choice, as it would surely get rid of excess humidity while an ERV would tend to keep it at a high level.

If the opposite is true and your house is too dry in winter, then an ERV would be a better choice as it helps retain humidity, eliminating the need (and cost) for you to generate it through other means.

In summer time, the use of an HRV will usually increase the humidity level inside your home, so an ERV is better in hot and humid zones. But a dedicated dehumidifier will likely do the trick much better. At the very least, the ERV will lower the load on the air conditioning system, even if it can’t keep up with the high humidity level on the outside.

So in the end, there is not one right choice between ERV & HRV systems. It depends on your climate, your lifestyle and your home. In a perfect world we would have one of each, or an integrated system that monitors and adjusts the internal air quality automatically, short of that we are left to make a choice.

One thing is for certain though, whichever you choose, an airtight home with an ERV or HRV is an evolutionary leap beyond the leaky houses of the 20th century, so if you are building or renovating a reasonably airtight house, especially if going for Passive House or LEED certification, don’t lose sleep over which one to get, ERV or HRV – just get one.

For greater peace of mind and confidence, book an appointment with us to start improving your indoor air quality..

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