A Healthy Home is well ventilated. Everyone knows fresh air is important. This should be easy. Well ventilated in more than just bringing in fresh air. The concepts are certainly easy, the details on the other hand take some thought and planning. A new home ventilation strategy is fairly straight forward to design and implement. An existing home needs the input from the occupants and good analysis to address the problems. An effective ventilation strategy should address these issues in either new or existing homes.
- Remove humidity, odors,, or significant problems from specific areas.
- Remove stale, musty or other objectionable air.
- Allow the occupants to choose fresh air sources that can be filtered or treated in other ways
- Allow the occupants to choose to open windows when outside weather is appropriate
- Allow the occupants to operate a system that can provide the amount of fresh air, to the appropriate places, in adequate amounts when needed
- Provide fresh air when the outside air creates potential problems, such as Ragweed season or when other allergens are active
- Provide air movement within the home, without the use of the expensive blower on the furnace or heat pump.
- Allow minimal use of heating or cooling equipment during the shoulder seasons, when temperature changes are minimal, while keeping the home comfortable.
How much fresh air is needed? Going back to the 1890’s, the number has been pegged at 30 CFM (cubic feet per minute) per person. This number was validated in a number of different studies and with the public health authorities in larger cities, dealing with large apartment buildings and recurring respiratory diseases. I was pointed to the quote at the left by Allison Bailles. he located the original book on Google Books, page 20.
Beginning in the 1930s, research into changes in building techniques began to show the optimal number was closer to 15 CFM per person. Some of the changes in construction included the increased use of forced air heating, moving from balloon framing to platform framing, increasing square footage, and the use of insulation in walls and attics. The formula changes from time to time and everyone has an opinion on details. The common point remains, fresh air is needed in every house.
Part of the Ventilation is removing air with a problem. Where is that? Humidity is found in rooms that use hot water and basements. Showers, tubs and cooking are the large sources of humidity. The smells from food preparation and cooking can be very mouthwatering. When the meal is finished and the refrigerator is full, the lingering smells become odors. The answer is some spot ventilation in these areas. If your basement has a humidity problem, you can tackle that with a fitted sump pump cover to contain the humidity, and work to eliminate any water seepage.
Spot ventilation is a window that opens and an exhaust fan. The size of these fans is part of the formula that is specific to each home. The features of the fan are common to all homes. It must be quiet. Builder grade fans are noisy. Noise in fans is measured in ‘Sones’. The Sone is a linear measurement of noise, compared to the decibels used by OSHA and others which is an exponential measurement. Linear is better for quiet sounds, and decibels is better for loud noises. Fans should be less than 3 sones, and preferably less than 1 sone. Reasonably priced fans are available that rate a 0.3 sones. A 1 sone fan is very quiet.
Fans are certified for air flow and noise levels by the Home Ventilation Institute. HVI certification is very common and includes both the Sone rating and CFM rating. When installing a fan, you must consider the duct losses that will occur in meeting the required air flow. The rates for bathroom air flow are 50 CFM, and 100 CFM for a kitchen. Do not expect to buy a 50 CFM fan for a bathroom and connect it to 6 or 8 feet of duct work, and obtain 50 CFM. I have measured 30 CFM routinely in these set ups.
Most people understand that various parts of their body are just a part of the whole. If you start some type of therapy, there may be a side effect. Physical Therapy starts and you end up with some sore muscles, aha! Side Effect! Start a therapy for cancer and your hair may fall out, aha! Side Effect! Your home works the same way. Each part is just part of the whole. Change something, aha! What is the side effect?
All of the items in the list above are part of the whole. For an existing home, some specifics of that house may indicate concentration on one or another of those areas. A home built in the 1920’s will benefit from a different approach then a house built in the 1980’s.
A new home should have the ventilation system that meets the general points above. The natural ventilation provided when windows and doors are opened, or the mechanical ventilation system that allows filtered and perhaps treated fresh air brought in from specific places and in specific amounts, allow the occupants to make the system work as they need.
This post is part of a Series on A Healthy Home