Ventilation and indoor air quality

This is #11 of my posts for the Sheffield Star Green Scene

“Ventilation is the intentional use of windows, ventilators, and fans to replace stale air with fresh air. Infiltration is the unwanted leakage of air through cracks in the house fabric and around windows and doors.” (Harris and Borer 2005 p.182)

Indoor air quality can be severely impacted by many of the modern materials used in our homes. This is not just an issue of bad smells and humidity. Carpets, paints, glues, cabinetry, furniture, cleaning and body care products, and even some insulation materials contain chemicals such as formaldehyde that have been shown to be carcinogenic. These products can be made out of all natural materials and care should be taken to source these options, however the chances are that your home contains something that is off gassing volatile organic compounds that are doing your health no good. Some areas have problems with radon gas coming from the earth below the house. This gas is dangerous and must be ventilated. Studies have shown that air quality next to roadways is very poor, even dangerous. Additionally, many people are allergic to mold and mildew to some degree which can produce unpleasant to severe symptoms.

As you seal up your house, reducing infiltration, you are also reducing air exchange. This can affect indoor air quality and moisture buildup and thus mold and mildew. In the most efficient of homes, such as the passive house designs from Germany the ventilation is actively dealt with through a heat exchanger to remove the old moist air while transferring it’s heat to the new fresh incoming air. These systems can be retrofitted in older homes but can be expensive. There are ways to maintain air flow without such an investment. Clearly there will be loss of heat with ventilation but some flow is necessary and you can reduce the losses through careful management of ventilation.

It is important to maintain air flow through your chimney to insure that the integrity of the construction doesn’t deteriorate. This will help insure adequate ventilation to any rooms that have fireplaces. But if you have been quite thorough at blocking ingress of outside air around windows, doors, floors, and services then you may need to find a way to allow a trickle of air to flow in. It is important to control where that air comes from, for instance, in the winter bring it in from the south or warm side of the house. We built a south facing conservatory onto our victorian terrace and used it to preheat the air we allowed to flow through the house while simultaneously blocking air from the north or cold side of the house. Fortunately, the south side of our house was not the road side, thus we avoided bringing in car exhaust. Similarly, try to ventilate at the warmer times of the day and not during high auto traffic periods. Unless you have severe air quality issues this level of control should suffice.

Another of avenue of ventilation is the hood fan on your cooker or bathroom. There are small heat exchanging systems available for these single room options. (Harris and Borer 2005 p.188) Combustion of natural gas produces several dangerous by-products which can cause lung irritation and exacerbate asthma and bronchitis. Be sure to use the fan when you cook with gas. Moisture buildup in bathrooms stimulates mold and mildew growth. Unfortunately using an electric fan, either on the cooker hood or in a bathroom, uses electricity and while it may be necessary while cooking or showering, they should be avoided if possible.

In a typical victorian terrace with a loft renovation you can take advantage of the stack effect. As warm air rises to the top floor it will pull air in wherever it is available. Through careful control of outlet and ingress you can create air flow with minimal losses. This method can be helped along with clever use of ductwork and fans if necessary. If you insure that the incoming air is preheated in a south facing conservatory or is at least sourced from the warm side of the house, it will minimize heating losses and may help to heat the house as it passes through.

References:
Harris, C. and Borer, P. 1998 - The Whole House Book; Ecological Building Design and Materials 2nd edition,