Written by Leo Sharkey, Owner
We recently received a call from new homeowners about high humidity levels in their brand new (2020 build) house. Upon inspection of the house, it was structurally well built. The HVAC system met code but was not state-of-the-art design. I’ll explain what I found, why that caused issues and what we are going to do to remedy the situation.
What We Found
The home was in a new development with big lots and ample space in the home. The HVAC equipment was a top-of-the-line brand name with a single furnace in the basement and two zones – one for the first floor and one for the second floor. There was nothing wrong with the existing equipment. The problem was that the house had been built to modern construction codes, which meant that the building was very well sealed and very well insulated, which is great, but does present some challenges. Old homes (anything built prior to the mid-1980’s) were highly porous with lots and lots of ways for air to enter and exit the home. New homes are more like a sealed plastic box – nothing enters, nothing leaves. This is a bit of an exaggeration, but I’m trying to make a point. Older homes “breathe”, new homes do not.
Imagine (don’t try this at home) putting a large garbage bag on your head and breathing for a few minutes. It won’t be long before the air in the bag gets very humid and the carbon dioxide builds up from your breath. The plastic bag prevents your breath from leaving and the by-products fill up the bag. This is what was happening in this new home. There were four occupants who breathed, lived, bathed, washed dishes, etc. in the home and the humidity had nowhere to go because of the sealed nature of the home.
What Caused the Home’s High Humidity
As I said earlier, the home met building codes, but wasn’t state-of-the-art. There were no controlled air exchanges going on in the home to dilute the built-up carbon dioxide and there was nothing to control the high humidity. In an old home, outside air would move in and out of the home diluting the carbon dioxide. In the winter, this outside air would be very dry and dry out the house as it moved through. In the summer, the outside air would be more humid, but because the house was much less well insulated, the air conditioner would run more/longer and pull the humidity out of the house. With modern construction, the homes are much better insulated and better sealed. Air doesn’t move through the home and the cooling load is much smaller, so the equipment doesn’t run as long or as hard and doesn’t pull out enough humidity from the air. So, how do you fix this problem?
How We Create Humidity and Ventilation Control
There are two things that need to be done to fix the indoor air quality at our client’s home. One, to control the carbon dioxide build-up, we need to introduce controlled ventilation for the home. We’ll install an ERV – Energy Recovery Ventilator, which is a big fan box that pulls in fresh air while simultaneously exhausting stale air and crossing the two streams to recover heat and humidity through what could be thought of as a heat/vapor exchanger. The how’s and why’s are not important, the important part is that we’ll control the amount of air moving in and out of the home and we’ll do that based on carbon dioxide levels. Outdoor air has roughly 400 parts-per-million of carbon dioxide. Stale indoor air in a well-sealed and poorly ventilated house can be two, three or four times that high. We’ll install a carbon dioxide monitor in the home and use that to control the ventilation. When the carbon dioxide level is high, we’ll run the ventilator until the level drops to our setpoint.
The second thing that we’ll do, and this is especially important in well insulated buildings, is install a whole-home dehumidifier. This will allow the air conditioning system to work on temperature control while the dehumidifier works on humidity control. This will be important in the spring and fall when the home requires very little heating or cooling input to maintain temperature, but the humidity levels might still be very high because of the occupants living and breathing in the space.
When we’re finished, our clients will have a well-controlled home with just the right levels of humidity and fresh air for the most comfortable home in the neighborhood.
Have an HVAC issue of your own? Reach out to us by phone (978)-534-9483 or through our website!
Specializing in indoor air quality & comfort, Jay Moody HVAC provides Central Massachusetts with highly efficient HVAC systems and service.
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