Maintaining optimal indoor humidity levels in cold climate houses has evolved greatly, with the introduction of heat-recovery ventilators (HRVs) and energy-recovery ventilators (ERVs), whole house humidifiers and the increasing sophistication of controls in “smart” thermostats. The flip side of this progress is that not all of them work together automatically and residents often don’t understand the systems that make their homes comfortable.

Fortunately, says Gord Cooke, President of Building Knowledge Canada, there are established strategies for optimizing these systems, which he details in an article originally published in Spring 2020 in Better Builder Magazine. These strategies aim to provide comfortable levels of humidity in winter while saving water.

Aiming for comfort and water efficiency

For most Canadian homes, optimal relative humidity (RH) is 35% to 40% in winter, to balance personal comfort with minimizing condensation on windows. This is not hard to achieve but builders often oversize the humidification systems which can waste energy and water.

Key considerations in determining the right humidification for a home are:

• Mechanical ventilation at design conditions which the builder generally knows and can factor in easily, using a psychrometric chart that maps ventilation requirements against outdoor weather conditions.
• Natural leakage in a home which should be determined through a blower door test along with the size of the home. Energy-simulation software such as HOT2000 can translate blower door test numbers into average winter air leakage rates. Tighter homes require less humidification.
• Moisture generated by the residents. This is a wild card, depending on the number of occupants and their lifestyle—elements such as how much they cook and shower, how often they are home, and so on. But it’s not insignificant: the average family of four puts 8 to 12 liters of water per day into a home.

With these factors in mind, Gord says, builders can choose the control systems that optimize winter humidity levels.

Strategies

Given this background, Gord points to five key strategies to minimize water waste related to humidification:

• Always aim to build tighter homes.
• Ensure that the ventilation system is balanced at the required ventilation rate, and switch to an ERV to cut water needs for ventilation by at least half.
• Use a reliable, calibrated hygrometer to measure RH levels accurately; then, help your clients understand that 35% to 45% RH is an appropriate range for both comfort and building integrity.
• If you install a humidifier, use the actual airtightness and ventilation rates to properly size it, especially in large homes where the operating cost of humidifiers will be highest.
• Choose humidity controllers with good water-flow controls that adjust humidity settings in response to outside temperatures, thereby reducing window condensation potential.

Optimizing humidification systems depends on understanding not only the technologies but also the home and its residents. Building Knowledge Canada has established expertise in how these factors work together and can help builders and contractors understand how to integrate them. Get in touch to see how we can support your design and business goals.

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_{Originally published in Better Builder Magazine, Issue 33 / Spring 2020.}

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