ERVs 101: How energy recovery ventilators work to maximize your home comfort

At a bare minimum, your home is designed to keep the outside out and the inside in. As building materials and installation practices have improved over the decades, homes have become even stronger barriers against the elements. Advanced insulation, air sealing techniques and high-performance windows and doors are just a few of the approaches builders use to tighten up homes, increase their energy efficiency and keep conditioned air inside where it belongs.

Or does it belong there?

While your dad probably told you he’s not paying to heat and cool the outside, he may have discounted the importance of bringing fresh air back into the home. Tightly built houses don’t just keep conditioned air inside — they keep all the indoor air pollution there too. In fact, the air quality inside your home could be as much as 5 times more polluted than the air outside.

Thankfully, other advanced building products exist to solve this problem. One of the best ones is called an energy recovery ventilator (ERV), and your dad will love this one. Let's look closely at how ERVs work, why they’re important and key considerations for choosing an ERV for your home.

What are energy recovery ventilators?

Energy recovery ventilators are incorporated into home mechanical systems for the purpose of moving stale air out of the house and bringing fresh air in. This may sound like the same purpose as your traditional heating, ventilation and air conditioning (HVAC) system, but there’s one key difference: While your furnace and air conditioner simply expel indoor air and replace it with outdoor air, ERVs are designed to transfer heat and moisture as part of the air-exchange process.

This function is where ERVs earn the “energy recovery” portion of their name. The heat and humidity in your conditioned air is exactly what your dad — and now you — pay for with every monthly utility bill. In fact, heating and cooling costs make up 55% of your utility bills.

“ERVs are simply designed to bring fresh air in from the outside and take inside air and move it out,” says Ken Nelson, group sales manager for Panasonic Eco Systems. “But let’s say you’re in a climate zone where it’s 30 degrees outside and you want to keep your home at 70 degrees. An ERV migrates the heat energy from the outgoing air into the incoming air stream, lowering the work your furnace has to do.”

By retaining this heat and humidity, your furnace and A/C don’t have to work as hard to condition incoming air. The result is more comfortable — and less polluted — air inside your home, and lower utility bills for your wallet.

Panasonic WhisperComfort 60, photo courtesy Panasonic Eco Systems

How do energy recovery ventilators work? 

Picture an ERV as a metal box with two parallel pipes running through it. Each pipe has a fan, which blow in opposite directions. One fan exhausts stale air to the outside, and the other pulls fresh air in. Between the two pipes, a permeable “transfer core” sits inside the center of the box. Its heat-conductive material looks similar to the filters in your range hood or the fins of your air conditioner. 

With the fans running, the indoor and outdoor air streams move in opposite directions and pass each other as they move through the transfer core. Inside the core, the first law of thermodynamics takes over: Heat moves toward cold. As a result, the cooler air stream absorbs the heat and humidity of the warmer air stream. 

What does this look like in practice? Let’s consider your home comfort in the summer:

Your air conditioner works to cool your indoor air to a comfortable temperature. Inside the ERV, stale cool, dry air moves through the transfer core where it meets an incoming stream of outdoor air. This air is fresh, but it’s also hot and humid. Inside the transfer core, the heat and humidity of the outdoor air moves to the cool air and gets pulled back outside. What remains of the incoming air stream has a lower temperature and less humidity, making it easier for your air conditioner to maintain your home comfort.

In the winter, the direction of airflow is the same, but the heat exchange process works in reverse. The ERV exhausts warm air from the house and pulls in fresh, crisp winter air from outside. The indoor heat mixes with the fresh air on its way in, and your furnace breathes a sigh of relief. 

ERVs & IAQ: Reducing Your Indoor Air Pollution

Speaking of which, you’re breathing easier with an ERV too. While heat and moisture are exchanged in the transfer core, indoor air pollutants are not. From bacteria and viruses to allergens and fireplace soot, ERV filters help improve your indoor air quality as much as they do your home comfort.

“ERVs aren’t performing magic or using technology like UV lighting,” Nelson says. “They simply take particulates in the air and move them out of the house so we’re not breathing them in. Additionally, if you’re going to bring in outside air mechanically, code requires that it be filtered on the supply side.” Together, he says, this means no lingering odors, fewer triggers for health issues like allergies and asthma and generally improved indoor air quality.

This is true during any season, and even when the heating and air conditioning systems aren’t running. During comfortable spring and fall days (or any time of year in more temperate areas), you can give your HVAC a rest while the ERV continues to move air throughout the home.

How to choose an ERV for your home

ERVs come in a variety wall- and ceiling-mounted models for every application from new construction to retrofit. This makes it easy to boost your air quality and your home’s energy efficiency no matter if you’re building from the ground up or have lived in your home for years — but there are certain considerations to make.

Proper sizing

The size of your home will dictate the capacity of the ERV to properly ventilate your space. A larger home will require a higher airflow rate, for example. The Air Conditioning, Heating and Refrigeration Institute (AHRI) says ERVs are typically sized to ventilate the whole house with at least 0.35 air changes per hour (that is, all the air in the home is replaced with fresh air once every three hours). To calculate the proper ERV size, take the square footage of your home and multiply by the ceiling height to get the cubic volume. Divide that figure by 60, and multiply by 0.35 to get the appropriate ERV size.

Configuration and Maintenance

Nelson says where you plan to put the ERV in your home and how you plan to service it go hand in hand. Just like your home’s furnace filters, ERV filters have to be changed as well. Be sure to install your system where you'll have easy access to the filter location. If you plan to install your system in a hard-to-reach area, such as an attic, Nelson suggests discussing the option of a remote filter box to make filter changes easier.

Climate

While ERVs work all year round, homes in colder climates will benefit from ERVs with higher heat recovery efficiency to prevent too much heat loss during ventilation. Conversely, in hot and humid climates, look for units that prioritize moisture transfer to prevent indoor humidity from building up.

Efficiency

Nelson says keeping an eye out for higher efficiency ERVs is a smart move. High-efficiency units will help your home accomplish indoor air quality and comfort goals more easily, and often at a statistically insignificant price increase. Look for energy efficiency between 75 and 80%, and consider the potential cost savings on your energy bills to offset any price differences.

Special Features

If indoor air quality is a higher priority in your home, whether to combat health conditions or for personal preference, look for an ERV with advanced filtration options. Other special features like multiple speed controls can also come in handy. Panasonic ERVs feature a “boost” function that lets you run the unit “low and slow all the time,” Nelson says, while increasing air changes during a party or other situations where indoor air pollution could increase.

Get Fresher Air into Your Home Today

Building technology has done a lot to improve the structure and energy efficiency of our homes, but we don’t want those improvements to come at the expense of our health. ERVs’ smart approach to ventilation with heat and moisture transfer brings clean, fresh air into your home, reduces indoor air pollution and does it all with an eye toward improving your home’s energy efficiency.

Incorporating this technology into your home couldn’t be easier, and doing so can help ensure that your home breathes easy — and your family does as well. Reach out to a Panasonic ventilation expert today to get started.