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Ventilation

This is a consumer page on ventilation. For more resources, visit the HVAC topic page.

When you think about it, energy efficiency is not just about saving money on energy bills, it is really about using less energy to protect human health, assure comfort, and protect your house from damage. As air moves through your house, it removes pollutants that include odors, gases, particles, and (most surprisingly) moisture. But, it can also contribute to drafty walls and uncomfortable indoor temperature and humidity levels. Proper ventilation and air distribution play an important role in providing a safe, comfortable, and durable home as efficiently as possible. Here's how to improve your house's ventilation:

Step 1: Eliminate Pollutant Sources
Step 2: Ensure Efficient Local Exhaust (Bathrooms and Kitchens)
Step 3: Filter Out Particulates
Step 4: Improve Whole-House Ventilation

 

Eliminate Pollution Sources

 

Control moisture. Moisture is one of the most important and least recognized indoor pollutants, affecting both human health and the health of the building. Where moisture collects, so do mold, mildew, and dust mites, which can cause asthma or allergies, destroy wood products, and accelerate the rusting of metal building components.

  1. Make sure that rain and gutters drain away from the building, not toward the basement or foundation (slab) walls.
  2. Grade the ground so it slopes away from the house.
  3. Make sure your house is properly air-sealed and insulated. Leaky houses give warm, humid air an excuse to pass through the house membrane and deposit condensation on cold wall surfaces. Control where moist air travels by installing local exhaust fans in kitchens and bathrooms. Very humid climates may require extra dehumidification appliances to control the excess water vapor.

Consider sealed combustion. Combustion products from gas appliances should never mix with the indoor environment. The terms sealed-combustion, direct-vent, and power-vented appliances all refer to appliances that vent their combustion products to the outside through a sealed pipe. Sealed combustion furnaces and water heaters are widely available and should always be used whenever located inside the conditioned space.

Check the garage connection. If your house has an attached garage, hire a professional to make sure the connection between your garage and your living space (including rooms above the garage) is airtight to prevent car exhaust and other chemicals from entering your house.

Use safe household products. Use pesticides and cleaning agents wisely and store them safely. Chemicals used in cleaning supplies, rug and furniture finishes, and paints fall within the class of indoor air pollutants called "volatile organic compounds" or VOCs. Consult the Green Building Resource Guide, the USGBC, or the Washington Toxics Coalition for product guidance.

Get a radon test. Radon is a radioactive gas that is generated naturally in the soil and enters the house from the ground. Radon is the second leading cause of lung cancer in the U.S. and its concentration in buildings varies regionally. Learn whether radon is a concern in your area at the National Safety Council Web site.

Quit Smoking. This one is fairly obvious but worth a mention. From both an indoor air quality and health perspective, few activities rival smoking in detrimental effects.

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Ensure Efficient Local Exhaust

 

Bathrooms and kitchens generate the most indoor pollution (moisture and VOCs), so when showering or cooking use a powered exhaust system that vents directly to the outdoors. Opening a window is often not enough.

Look for an ENERGY STAR-rated ventilating fan. ENERGY STAR fans are energy-efficient and quiet. In the bathroom, fans should be 50 cfm for rooms 100 ft2 or less to provide adequate ventilation without wasting energy. Range hoods are available in many sizes, but typically an up-draft range hood should provide 100 cfm of ventilation for wall-mounted hoods and 150 cfm for island hoods. They should always have a ducted passage to the outside that is fitted with a damper to prevent infiltration. To learn more or to see what products qualify, visit the ENERGY STAR Ventilating Fans page. A product list is linked in the upper right-hand corner of the page under "For Consumers." Products with higher efficacy (cfm per watt) are more efficient.

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Filter Particulates

 

One advantage to a forced-air heating and cooling system is that you get a built-in air filtration system to deal with free particulates such as soot, dust and pollen. This filter should be cleaned or replaced monthly during the heating season. There are two types of filters you can install to maximize the efficiency of your air distribution system when it's time to replace:

Mechanical filters. Mechanical filters trap particles like a sieve. The size of the smallest particles they trap well are measured by “MERV,” or “Minimum Efficiency Report Value.” MERV 4 or 5 is pretty characteristic of residential air filters. If you have allergies or other health concerns, you may want to consider MERV 8 or 9, but probably no higher: filters that remove finer particles cost more to purchase and have substantially higher resistance to airflow, requiring more fan energy.

Electrostatic filters. Electrostatic filters attract particles passing through the filter by electric charge. These are typically better than mechanical filters because they can trap very small particles without hindering air flow.

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Improve Whole-House Ventilation

 

It is recommended that houses always have some planned ventilation strategy that mixes stale air with new air and moves it through the house. Ideally, an energy-efficient and healthy house is able to carefully control the air that is coming in and going out, and to do so at just the right rate. Unfortunately, installing a well-balanced ventilation system is not feasible for most existing houses. The following strategies should help you understand how best to improve air quality throughout your house.

1. Opening windows. If it is cool or breezy enough outside, opening windows may induce enough fresh air into the house, forcing stale air out.

2. House fans. In a typical multi-story house during most of the year, air moves naturally upwards as it warms and rises. In mild climates, a fan placed in the ceiling or open attic will exaggerate or induce this "stack effect" when you open the windows, providing fresh air and cooling. Check with your nearest home improvement retail store about available products and correct installation.

3. Intermittent exhaust ventilation. If there isn’t much breeze and the air flow between inside and outside is static, operating a 100 cfm fan would continuously provide adequate ventilation for a 1,500 square foot house with 8-foot ceilings. This is an example of "exhaust-only ventilation." One downside is that exhaust-ventilation depends on uncontrolled infiltration to provide fresh air. In hot-humid climates, this strategy should not be used without careful supply air control. If hot and humid air is drawn into the building for months on end, condensation, mold, and damage are likely to develop.

4. Supply-only ventilation. Supply ventilation systems draw clean outside air into the interior living space, usually through a supply vent that feeds into the return duct of a forced air system. Aside from allowing incoming air to be carefully controlled and filtered, supply-only strategies tend to “pressurize” the house, which keeps moisture out in hot, humid climates but may induce drafts in cold climates as warm air escapes to the outside.

5. Air handler and duct maintenance. Approximately two thirds of U.S. houses use ducts to move heating and cooling energy from a central furnace, air conditioner, or heat pump around the house. This is not the same as ventilation — ducts control how air is distributed within the house, not how air enters and exits. But because virtually all duct installations leak, your air distribution system may be throwing off humidity levels and air infiltration rates in your house.

  • If your house has its heating and cooling equipment in an uninsulated basement or attic, make sure supply and return ducts are well sealed and insulated to minimize air exchange with the outdoors.
  • Your thermostat should have a switch for controlling the furnace fan. If so, make sure the fan switch is set to “auto” mode instead of "on." Continuous fan operation wastes energy and is likely to cause moisture problems.
  • If you live in a dry climate (or a place with cold, dry winters), and it is uncomfortably dry inside, check the fan speed on any ventilation equipment you might have installed before running out to buy a humidifier.

6. "Balanced" ventilation. Balanced ventilation is essentially a well-controlled combination of the exhaust and supply strategies, but it takes a very tight house and good engineering to get it right. Often, a balanced system involves a powered heat recovery or energy recovery ventilator (HRV or ERV) that improves efficiency and pressure balance by exchanging energy (from temperature and humidity differences) between the outgoing and incoming air streams. Unfortunately, it is rarely economical to install such a system into an existing house.

7. Stand-alone dehumidifiers. In hot climates on very humid days with moderate temperatures, air conditioners probably will not run enough to remove the moisture load. To find out whether you need a dehumidifier and to find a qualified product, visit the ENERGY STAR Dehumidifiers page.

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Page last updated December 2012