Improving Fresh-Air Ventilation
Many things work together for moisture control and indoor air quality. To improve energy efficiency and lower energy costs one goal is to make the house as tight as possible to take advantage of smaller equipment that doesn’t need to run as long.
Assuming other recommendations are implemented, the remaining question is whether continuous mechanical fresh-air ventilation is needed. The short answer is when natural air infiltration falls below 0.35 natural air changes per hour, mechanical fresh-air ventilation is needed.
Customer Targets for Fresh-Air Ventilation
This is the shopping list for fresh-air ventilation:
- Do no harm!
- High-quality fan: energy efficient & quiet
- Continuous operation
- Pre-conditions air before delivery
- Provides good air distribution
- Accessible for maintenance
- On-off switch
- Instructions for use
Do No Harm. Do not use any fresh-air ventilation system that will damage the house or injure the occupants. Gas water heaters and furnaces need to draft properly at all times. Moisture should not freeze in the walls. Air cannot come from potentially polluted places.
High-Quality Fan. To be acceptable to the people living in the house, the system must be quiet or it will be disabled. In terms of energy efficiency, more airflow per Watt (cfm/W) is preferred.
Continuous Operation. Fresh-air ventilation systems need to run continuously to avoid a buildup of unhealthy air, especially as manufactured products outgas: house, furniture, appliances, etc.
Continuous fans are quieter, smaller, and fit into house easier. There is no on-off noise. Finally, intermittent drafts of untempered air are eliminated.
Pre-Condition Air Before Delivery. Before using the air, particles such as pollen, dust, and debris need to be filtered out. In humid areas, air needs to be dehumidified as needed. Where there are temperature extremes, it may be worth warming or cooling the air a bit first.
Air Distribution. Air needs to be taken from or delivered to several rooms at once to help ventilate the house more evenly.
Accessible for Maintenance. Homeowners need to be able to change the filter. Ventilation system contractors need to be able to adjust the air flow to balance it.
On-Off Switch. The system needs to be able to be turned on and off. To avoid turning it off accidentally, the switch needs to be put in a little used area, such as a mechanical room or closet. The switch also needs to be labeled with instructions, including where the fan and air filter is so it can be maintained.
Instructions for Use. People are unfamiliar with the features of a high-performance home. Without education, they try to operate it like any other house they’ve lived in. With some education and use instructions, they are more likely to be used as intended.
Prepare House for Ventilation
There are a variety of best practices but no guarantees for moisture control and indoor air quality. Ventilation is the last step as ventilation cannot effectively provide either of these alone.
IAQ Priorities. Recommendations for improving indoor air quality amount to these four priorities:
- Remove sources of pollution.
- What cannot be eliminated needs to be reduced.
- What cannot be removed or reduced needs to be managed.
- After do everything else possible, use ventilation for what remains.
Moisture Control Priorities. Recommendations for moisture control follow these priorities. First, stop water leaks into and in the house. Second, avoid condensation. Third, eliminate or reduce unnecessary moisture vapor. Finally, use local exhaust ventilation in bathrooms, kitchens, and laundry rooms to move moisture vapor build up outdoors immediately. When necessary, use dehumidifiers, such as central cooling systems.
Improving Fresh-Air Ventilation
When the house is tight, moisture is managed, and best practices are followed for good indoor air quality, mechanical fresh-air ventilation may be effectively used.
System Installation. The chosen mechanical fresh-air ventilation system needs to be installed according to the manufacturer’s instructions, industry best practices, and comply with local building codes. When installed, it needs to be tuned for maximum performance.
Home Owner Education. Fresh-air ventilation systems are unfamiliar to most people. The installer should educate the homeowners where the system is, how to maintain it, how it works, what happens when it’s not working, and who to call for help. As your building consultants for life, we will help you too!
Post Mechanical Ventilation Testing
In the process of improving your home for better home performance, one or two types of ventilation systems may be installed: local exhaust ventilation and continuous fresh-air ventilation. Both systems should be tested for actual performance.
Our major concern is to do no harm after they are installed. When there are fuel-fired water heaters and furnaces, the areas they are located in need to be retested to ensure the safety of the occupants and protection of the house.
Where there are incentives or certificates offered, the sponsor (e.g., utility company) usually requires final testing too. Their considerations are to verify better equipment was installed and the systems perform properly.
We are ready, willing, and able to perform third-party testing.
In Conclusion . . .
In the home performance improvement process for moisture control and indoor air quality, the top three things are to eliminate sources, reduce what can’t be removed, then ma what has to remain. Ventilation should be used for what is left.
Local exhaust ventilation of bathrooms, kitchens, and laundry rooms are always necessary. Continuous mechanical ventilation becomes necessary when the building tightness limit is exceeded.
For best energy efficiency, the house should be as tight as possible. It’s cheaper to condition and ventilate a tight house than it is to condition a leaky one.
Here’s to a healthier, longer lasting, more comfortable, and energy efficient house!
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