Balanced Whole House Ventilation
Energy recovery ventilators (ERV) and heat recovery ventilators (HRVs) are large boxes that typically hang in a basement near the furnace. These systems connect with two ducts for supply and return of inside air, and two ducts that go outside for fresh and stale air. For those without furnaces, these units have dedicated ductwork throughout the house, with fresh air supplies going to bedrooms and living rooms and exhaust sides going to the bathrooms, laundry room, and kitchen.
HRVs and ERVs offer the ability to pull stale, moist air out of the rooms that generate it, and supply conditioned fresh air to the spaces that benefit most from it. HRVs are typically installed in cold climates and smaller homes and ERVs in hot climates or larger homes. Although, with climate change, ERVs are becoming more predominant.
Both of these units are essentially fancy radiators: as the warm, stale inside air goes outside, it goes through a radiator. This energy warms the incoming cold winter air, preheating it before sending it through the house. It does the opposite in hot conditions, pre-cooling the incoming air. The main difference between the two units is that ERVs also take out and transfer a small amount of humidity. It's not enough to get rid of your dehumidifier or air conditioner, but enough to help. Because of the heat transfer that occurs with HRVs and ERVs, they avoid the waste of your warm indoor air in the winter and cool, conditioned air in the summer.
Sounds Great, What Could Go Wrong?
Similar to almost any mechanical system, the things that can go wrong happen upon installation and maintenance.
Poorly Installed Mechanical Ventilation
Unfortunately, these units are often installed improperly. The often forgotten critical step is that they need to be balanced. Meaning the inlet pressure needs to equal the outlet pressure. The installer does this by throttling the inlet and outlet valves and measuring them at low and high pressures to get them as close to each other as possible. The units come with stickers that go on the front stating the installation date, the installer's name, the low-pressure balance, and the high-pressure balance numbers. If there is no sticker or writing anywhere on it, then it wasn't installed properly. At best, the unit is wasting energy; at worst, it is sucking dirty air into the house.
Poorly Maintained Mechanical Ventilation
Did the installer mention you have to clean the inlet screen outside? Did they mention you have to clean the filters inside the unit? Both are necessary and super easy to do. If you don't clean them, then the inlet screen will clog up (which is relatively common). If this happens, you are no longer bringing fresh air into the home. If you have one, check them now and clean them off.
What to Do With Your Existing Mechanical Ventilation System
If you have an ERV or an HRV, have a look and see if it is balanced. If not, when you have your yearly mechanical inspection, have it balanced (you may need to ask for this ahead of time). Note that if the installer is not going around the house and turning on all exhaust fans and dryers, they are not doing it correctly.
