Airtight homes trap moisture, leading to high humidity. Learn why your mini-splits aren't enough and how to use ventilation or dehumidifiers to fix it.
Based on reporting by Green Building Advisor. Research, structure, and fact-checking by Groundwork.
High humidity in airtight homes is usually caused by insufficient ventilation or short-cycling HVAC systems. Solve it by installing an Energy Recovery Ventilator (ERV) to exchange air or a dedicated whole-house dehumidifier to manage moisture independently of your cooling system.
If mechanical ventilation alone cannot keep indoor relative humidity between 30% and 50%, a whole-house dehumidifier is the most reliable, permanent solution. Unlike a mini-split, a dedicated dehumidifier is designed specifically to remove moisture without significantly cooling the air, allowing it to run independently of your heating and cooling system.
Standalone dehumidifiers can be integrated directly into your home’s ductwork or installed as a bypass unit. By setting the unit to a specific relative humidity target, you ensure that the air remains comfortable regardless of whether the mini-split is running. This approach is backed by research from the Department of Energy, which notes that controlling moisture is essential for preventing mold growth and protecting the structural integrity of a high-performance home.
To permanently resolve high humidity, you must follow a systematic approach that addresses both air exchange and moisture removal. Follow these steps to restore comfort:
Ironically, while summer brings high humidity, the same airtight construction can lead to excessive dryness in the winter. This occurs because the air exchange rate is low and the heating system further reduces the relative humidity of the indoor air. To combat this, ensure your ventilation system has a control that allows you to reduce the air exchange rate when outdoor air is extremely cold and dry, or consider a whole-house humidifier if levels consistently drop below 30%.
An Energy Recovery Ventilator (ERV) is generally better for humidity control in mixed or humid climates because it transfers moisture between incoming and outgoing air. An HRV primarily focuses on heat exchange and does not manage moisture as effectively in humid conditions.
The ideal indoor relative humidity is between 30% and 50%. Keeping humidity in this range prevents the growth of mold and dust mites while maintaining comfort for the occupants and protecting the home's structure.
Portable dehumidifiers are often insufficient for whole-house moisture control. They are typically noisy, have small tanks that require constant emptying, and lack the capacity to treat air across multiple rooms. A whole-house, ducted unit is the standard recommendation for high-performance homes.
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