Does a ‘green house’ require mechanical ventilation? Is this not one of the energy intensive methods that one should be trying to get away from? These are some of the questions that are heard when homeowners are asked to consider having a ventilation system. 

Why is ventilation important in today’s housing that is considered leak proof and well insulated for comfort? Older homes were very leaky. There were gaps, cracks, and holes all over the building’s structure. There was no insulation. This allowed fresh air to flow in and out of the house freely. Today’s houses are leak proof, and the insulated meaning air is trapped inside and becomes stale and unhealthy.

Today’s building materials include flame retardants, formaldehyde and other artificial building material containing chemicals. These materials have a lot of off-gassing of volatile organic compounds (VOCs) that are harmful when they build up in the house. 

Home Ventilation Options

There are a number of ways to ventilate your home or property, generally, there are 6 types of ventilation methods used.

• No ventilation: This can be seen in many homes.  The flow of air in a non-ventilated house depends on natural breeze and differences in temperature. This works for a leaky house. However, on calm hot days, such a house can get very uncomfortable

• Natural ventilation: This option uses design features of the house to facilitate the flow of air in and out of the house. A good example is a solar chimney which heats up air. This hot air rises lowering the pressure in the house.  Colder fresh air flows into the lower pressure through strategically placed ventilation holes.

• Exhaust-only mechanical ventilation: These mechanical systems are designed to exhaust stale air in places like the bathroom and kitchen. The exhausted air creates lower pressure in the house which allows in fresh air through air inlets. This method is simple to install and low in cost. The limitation of this method is that it does not filter pollutants like soil gases

• Supply-only mechanical ventilation: This system is designed to let in air fresh air, and have the stale air escape through the leaks in the house structure. Common configurations are air delivery to one point in the house, through ducts in different rooms, or through the heating system. The advantage of this system is the maintenance of high pressure in the house which prevents contaminants like radon flowing in. its disadvantage is forcing moisture laden air into the walls and roof, which can encourage mould growth.

• Balanced ventilation: This system uses separate fans for bringing in air, and exhausting stale air. The system can be configured to control the points at which stale air is drawn, and fresh air delivered.  The design can be point or duct system. In a duct system, fresh air is delivered to living spaces like the living room and bedrooms while stale air is exhausted from bathrooms and kitchen.

• Balanced ventilation with heat recovery: This is a modification of the balanced ventilation system to introduce heat and moisture control. It has an air-to-air heat exchanger also known as a heat-recovery ventilator (HRV). This unit transfers heat from outgoing air to the incoming air. A more sophisticated version is the Energy-recovery ventilator (ERV) that transfers heat to the incoming air and moisture to the outgoing air. This maintains the temperature in the house while keeping humidity levels low.

It is advisable to have a ventilation system even in leaky houses. This keeps the house comfortable when the pressure differentials fail to facilitate air circulation. As mechanical ventilation is energy intensive, it then makes sense to install a ventilation system with energy recovery. This is what a ‘green house’ would need to breathe optimally.