Adding Insulation To An Existing Home -- Ventilation Concerns
Adding Insulation To An Existing Home
The Purpose Of Ventilation
Every home needs ventilation, the exchange of indoor air with outdoor air.
There are a lot of contaminants that can plague the health of the home and the health of the homeowner. Volatile organic compounds (VOCs), allergens and radon can accumulate in poorly ventilated homes. Excessive moisture can lead to mold growth and structural problems. Ventilation reduces indoor pollutants, moisture, and odors.
How Much Ventilation?
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) suggests that a home's living area should be ventilated at a rate of 0.35 air changes per hour or 15 cubic feet per person per minute, whichever is greater.
Types of Ventilation
Natural ventilation occurs when there is uncontrolled air movement or infiltration through cracks and small holes in a home -- these are the areas the previous insulation post talked about sealing. So we'll eliminate natural ventilation as a strategy.
Spot ventilation includes the use of localized exhaust fans (like in bathrooms and above kitchen ranges). ASHRAE recommends intermittent or continuous ventilation rates of 20 cubic feet per minute for bathrooms and 25 cubic feet per minute for kitchens.
The third type is a whole-house ventilation system. This provides controlled, uniform ventilation throughout the house by using fans and duct systems to exhaust stale air from the house and supply fresh air to the house.
There are four types of whole-house ventilation systems:
- Exhaust ventilation systems
- Supply ventilation systems
- Balanced ventilation systems
- Energy recovery ventilation systems
Exhaust Ventilation Systems
These systems depressurize the house, making the inside air pressure less than the outside air pressure. This in turn extracts the inside air from the house while while make-up air enters through passive vents.
Exhaust ventilation systems are relatively simple and inexpensive to install.
Supply Ventilation Systems
These work the opposite way and pressurize the house. A fan forces outside air into the building while air leaves the building through vents. By pressurizing the house, supply ventilation systems discourage the entry of outdoor pollutants into the living space. It also prevents backdrafting of gases from fireplaces and appliances.
Supply ventilation systems are relatively simple and inexpensive to install.
Balanced Ventilation Systems
If properly designed and installed, a balanced system won't pressurize or depressurize a house, instead introducing and exhausting equal quantities of fresh outside air and polluted inside air, respectively.
A balanced ventilation system usually has two fans and two duct systems. It facilitates good distribution of fresh air by placing supply and exhaust vents in appropriate places. Fresh air supply and exhaust vents can be installed in every room.
Energy Recovery Ventilation Systems
These systems provide a controlled way to ventilate the house while minimizing energy loss.
They reduce the costs of heating ventilated air in the winter by transferring heat from the warm inside air being exhausted to the fresh (but cold) supply air. In the summer, the inside air cools the warmer supply air to reduce ventilation cooling costs.
Those are the ventilation options. Next we'll look at the areas to insulate.
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