The reason HVAC contractors put fresh air in a home is to combat CO2 build-up and pockets of stale air. The main reason is CO2 build up. First off you have to know what type of house actually needs fresh air. The only type of house that is tight enough to need fresh air is a spray foam house; any other house that does not need fresh air is not tight enough to need fresh air. Secondly, it’s important to talk about how to install fresh air into a home without damaging the equipment or causing the home to be freezing in the winter, hot in the summer, and if in a high humidity area (like the South) wet and swampy through out the year.

So spray foam houses are sealed tight enough that CO2 build up actually becomes a real concern and you can get pockets of stale air because it is just the same air bing recycles over and over, but stale air is not really a concern it’s more of a byproduct. The real concern is that if you stayed in your home for a given amount of time and never left or opened a window you could die from running out of oxygen in a spray foam house. Now this is something that would be extremely rare of course, but that is how fresh air saves the day by recycling oxygen back into your home. If you do not have a spray foam house then this is not a concern your house will never be sealed tightly enough to not allow outside air to penetrate into the home.

Installation Process

So we have established you have a spray foam home and you need fresh air. How do we install this fresh air properly? Well, there are only 2 ways to properly install fresh air. First off it needs to be calculated into the load of the house as your size your system to determine how large the duct should be, but relatively it’s not very big generally around 100 cfms. Second, you will need one of 2 machines. The first type of machine is called an ERV and the second is called an HRV. HRVs are heating recovery ventilators, and they are mostly for northern climates with drier air and colder temperatures. This way as the fresh air comes into your house it’s not cold air that then imbalances the load of your home and causes your system to not keep the house at the temperature you desire it to be. The other which is what we would need here in the South is an Energy Recovery Ventilator. This ventilator removes the moisture from the damp air we have here in the South, and also conditions it back to a temperature relative to the temperature inside the home, thus reducing the load put on the system trying to cool/heat and dehumidify your home. This type of ventilator works for heat & air conditioning and focuses on reducing the humidity of the fresh air it is interacting with. A spray foam house in the South HAS TO HAVE AN ERV for you to have a fresh air hook up on your HVAC system. There is no if, ands, or buts for this. Your system will not work correctly without an ERV if you are bringing fresh air into your HVAC system.

If you install a fresh air duct into your HVAC system and you do not have an ERV then your system will quickly rust out, you’ll always have moisture issues around your air handler and ductwork, and your home will never dehumidify properly (and in most cases you won’t even be able to maintain a set point temperature in the summer time). Without an ERV your system will fall apart, break down, and your home will be entirely uncomfortable and your electric bill will always be high. If you do not have a spray foam house and can not afford an ERV then the solution is simple remove the fresh air duct and seal up the hole with spray foam.