Cutting Your Utility Bill: How can we get more fresh air indoors?

This is fuly-ducted fresh air heat recovery ventilation syste. Notice the air outlest ar in many of the homes

The outgoing stale air and incoming fresh air exchange heart and moisture in the heart-exchanger compartment.

Dear Jim:
We made efficiency improvements over the years, but the indoor air often gets stale. Without negating all our efficiency investments, what ways can we get more fresh air indoors?

— Laura T.

Dear Laura:
Stale air and a buildup of pollutants are common problems as people tighten up their houses to save energy. According to the Environmental Protection Agency, people typically spend 90 percent of their time indoors. Common symptoms of poor indoor air quality include irritation of the eyes, nose and throat, headaches, dizziness and fatigue. Radon gas can be a cancer risk as great as smoking.

The purpose of bringing in fresh air is twofold. First, when fresh air comes in, polluted stale air must go out or your house would explode. Secondly, fresh air dilutes the pollutant concentrations of the stale air remaining indoors. In addition to providing fresh-air ventilation, try to minimize the gaseous and particulate pollution you generate indoors.

There are four basic mechanical methods to introduce fresh air into your house, and each has advantages and disadvantages. The simplest is an exhaust-only system. This often uses a central ducted vent fan to depressurize the house. This draws fresh air in through gaps and leaks in the house exterior. Passive inlet vents can be installed in an airtight house such as yours.

This is the least expensive system to install. This works best in cooler, low-humidity climates, especially during summer. Its drawback is the fresh air may not be distributed evenly throughout the house. It will increase utility bills slightly and may cause chilly drafts during winter. If you have gas appliances, backdrafting may be a problem.

Supply-only systems use ducted fresh air fans to create a positive pressure indoors. This forces the stale indoor out through cracks in the exterior. It is simple and inexpensive to install, like an exhaust-only system. Its primary advantage is the incoming air can be filtered and it provides better control over the fresh air flow. Also, it will not cause backdrafting of gas appliances.

A balanced system uses a combination of ducted supply- and exhaust-only systems. This provides better control of the ventilation because it does not rely on just cracks or leaks in the house exterior. It costs more to install because it requires two ducted systems. It uses more electricity because it runs two sets of fans and it does not control incoming summertime humidity.

A heat recovery ventilation, or HRV, system is the most efficient and expensive (typically $1,000 to $2,000) balanced system. During winter, heat from the stale outgoing warm air is transferred to the incoming cold fresh air. During summer, the stale outgoing cold air precools the incoming hot outdoor fresh air. Up to 75 percent of the energy in the air can be saved.

A HRV is a simple system with a heat exchanger inside a cabinet and two separate blowers, one for incoming air and one for outgoing air. It has its own duct system, drawing the stale indoor air usually from bathrooms and the kitchen. The incoming fresh air ducts often lead to the living room and hallway.

In many climates, indoor humidity levels are also a concern. During summer, bringing in precooled humid air may not greatly improve comfort and may exacerbate allergies.

Excessively dry air during winter can be uncomfortable for the skin and can cause other health problems.

An energy recovery ventilation, or ERV, system has a special heat exchanger to also transfer moisture. During the summer, the incoming fresh air is partially dehumidified by the outgoing cool dry stale air. During winter, the indoor humidity is recaptured. System speed and run-time are controlled by a humidistat or programmable timer.