We all want homes that are comfortable and energy efficient. But all our efforts to replace drafty windows, seal up air leaks, and blanket wall cavities with insulation have had an unfortunate consequence: They’ve made the air in our houses less healthy to breathe.
More of the airborne pollutants that once might have found their way outside—household chemicals, smoke, pet dander, and cooking gases, to name a few—are building up inside. Our well-intentioned efforts to restrict the flow of air in and out of our houses have led to indoor air-pollution levels that can be two to five times higher than those outside, according to the Environmental Protection Agency.
Indoor Air Quality
That doesn’t mean we should give up on making our houses tighter, of course. But it does mean now is a good time to pay as much attention to indoor air quality, or IAQ, as we do to energy efficiency.
That begins by getting a better understanding of how to balance the movement of air in and out of a house, and of mechanical systems that usher in fresh air and expel stale air without compromising energy efficiency—or comfort—in all seasons. Monitoring your IAQ is a useful first step in raising awareness, too. Because when we know what we’re up against, and how to minimize our exposure, we can all breathe easier.
Ventilation is the key to good indoor air quality. In the past, houses mostly relied on natural ventilation—air moving freely through windows, doors, and leaky walls—to flush out stagnant, contaminated air.
But sealing a house to prevent energy loss halts the healthy level of air exchange you get with natural ventilation. In 2012, as building codes demanded tighter construction for energy efficiency, requirements were added for whole-house mechanical ventilation. As TOH expert Richard Trethewey puts it: “If you’re going to insulate, you’ve got to ventilate.”
In most existing houses, mechanical ventilation is limited to bath fans and range hoods that exhaust steam or cooking odors. These fans remove the bad air, but often the fresh air needed to replace it—called makeup air—simply slips in through cracks in walls, down chimneys, and through basements and attached garages.
Not only is this air as hot or cold as the air outside, it’s very likely picking up contaminants on its way in. Extreme lack of makeup air can cause dangerous back-drafting of combustion appliances such as furnaces and gas-fired water heaters.
“It’s a balance between getting fresh air and not wasting energy.”—Richard Trethewey, TOH plumbing & heating expert
Energy Recovery Ventilator
A home’s ventilation system should balance the amount of air going out and coming in. And to save energy, you want to make sure the energy used (and paid for) to heat or cool your home doesn’t flow out with the stale air.
Enter the energy recovery ventilator, or ERV. This box-like device moves air in and out of the house while conditioning it to about the same temperature and humidity level as the air inside. You get fresh air, customized for a healthy, energy-efficient home.
An energy recovery ventilator ensures a steady supply of clean, conditioned air.
How does an ERV work?
Two fans draw air into the ERV: One brings fresh air in from outside the house, the other draws stale air from inside. The two airstreams are channeled past each other—but do not mix—in an exchange core made of a conductive material such as aluminum or plastic that allows the heat and moisture from one stream to transfer to the other. The ERV may be programmed to run periodically on its own, or may be activated along with a furnace blower.
The way fresh air is moved through a house via an ERV depends on factors such as the presence of existing ductwork, the age and efficiency of the furnace, and the layout of the home. Usually an ERV is tied into existing ductwork in a forced-air system (as shown, below). But an ERV can also be installed independent of the HVAC system, along with its own 6-inch ducts. This approach is typical in homes with electric or hydronic heat.
ERV system cost
ERV units cost between $800 and $1,500, with installation running $1,000 to $2,000, depending on the scope of the work. Some states offer rebates; to see if yours does, check the database of the NC Clean Energy Technology Center.
Balanced Ventilation System
This home’s balanced ventilation system relies on an ERV tied to an existing forced-air HVAC system. Along with kitchen and bath fans, it maintains indoor air quality without compromising energy efficiency.
1. ERV intake
Fresh air is drawn in through a duct and passes through the ERV’s core, where heat and moisture are exchanged. In this case, cold winter air is warmed by the outgoing conditioned air so the furnace does not have to work so hard to bring it to room temperature.
In this home, air that is conditioned by the ERV passes through the furnace, where it is fully heated and then distributed through the HVAC ductwork.
3. Air return
Stale, conditioned air from bedrooms and living areas is drawn back toward the ERV, where most of it is exhausted outside after transferring its heat to the incoming air.
4. Bath vent fan
Odorous, moist air that can lead to mold and mildew vents directly outside to prevent recirculation through the house’s HVAC system.
5. Range hood
Cooking gases drawn through the range hood are ducted outdoors. This high-powered hood requires dedicated makeup air, which enters through a vent behind the cabinet that is activated when the vent fan is turned on.
6. Sealed fireplace
A sealed insert helps control both indoor air pollution and energy loss by sending combustion gases up the chimney, not into the room.
Other ways on how to improve indoor air quality
While a balanced system of mechanical ventilation is the most effective way to improve indoor air quality, here are some more steps you can take.
Boost your existing exhaust system
Make sure bath fans vent outdoors (and not into a ceiling or attic). Run them for 20 minutes each time the room is used, or install a switch that activates the fan when the lights come on. Replace a recirculating range hood fan with one that vents outside, and, if you can, add a makeup air damper nearby that opens when the hood is operating.
Upgrade air-handler filters
Filtration is no substitute for ventilation; still, regular replacement of your air-handler filter or, better yet, upgrading to a more effective electrostatic filter can cut down on the recirculation of irritants. Look for a filter with a MERV (minimum efficiency reporting value) rating between 11 and 14. Check filters monthly and replace if dirty, or at least every six months.
Spot-clean the air
Stand-alone air purifiers can effectively remove airborne contaminants in a confined space, says the EPA. Some filter both gases and particulates; others address one or the other. The Association of Home Appliance Manufacturers’ Verifide program tests air cleaners’ performance; check ratings at AHAM Verifide.
Shut the door on pollutants
Seek out no-VOC paints, cleaning products, and furnishings; look for third-party green certification seals. If you must introduce chemicals into your home, buy only what you need, and dispose of leftovers promptly.
Indoor Air Quality Testing
New interest in IAQ has led to a wave of devices that will keep tabs on your home’s air quality. Many will alert you via smartphone to changes in IAQ, or communicate with your smart thermostat to activate the ventilation system. “Knowledge is power,” says TOH home technology expert Ross Trethewey.
Decide what pollutant you want to monitor.
Not all devices track all pollutants. If someone in your home is allergic to dust or pollen, for example, you’ll want to make sure the one you select tracks those specific particulates.
Pay attention to the sensor.
The sensor is the most critical part of the monitor. A table of sensors tested by the EPA is available at epa.gov/air-sensor-toolbox. Be prepared to pay more for a good one.
Consider the next step.
Knowing that your indoor air is unhealthy only gets you so far. A monitor that can trigger ventilation either directly or through a smart thermostat ensures a quick response to poor IAQ.
Choosing an Indoor Air Quality Monitor
The Foobot tracks tiny respirable particulate matter (PM2.5), total VOCs (TVOCs), temperature, and humidity. Its LED display indicates overall air quality by glowing blue (good) or orange (bad); the app rates your IAQ on a numerical scale from 0 to 100.
AWAIR GLOW C
The retro-styled Awair 2nd edition (left) tracks temperature, humidity, CO2, TVOCs, and PM2.5. The plug-in Glow C measures only TVOCs, temperature, and humidity, but will trigger “non-smart” devices like air purifiers or fans that are plugged into it.
$199 and $89; Awair
With a clock-like appearance, both the Laser Egg (left) and Laser Egg+Chemical track PM2.5, temperature, and humidity; the latter also monitors TVOCs. Both are Wi-Fi-enabled and work with other home appliances via Apple Homekit and IFTTT.
$149 and $199; Amazon
The Temtop M10 has no Wi-Fi connectivity and no app, but offers at-a-glance readings of PM2.5, TVOCs, and formaldehyde with a series of clicks. Two other versions are available: The P10 measures only particulates; the M10i offers Wi-Fi connectivity.
The AirVisual Pro rates household air using EPA’s Air Quality Index of 0 (good) to 500 (hazardous) and compares that score with locally reported conditions. It tracks PM2.5, temperature, humidity, and CO2, and recommends remedial action when IAQ is poor.
WAVE PLUS AND MINI
The Wave Plus (shown) monitors temperature, humidity, air pressure, TVOCs, CO2, and radon, but not particulates. The desktop Wave Mini tracks temperature, humidity, air pressure, and TVOCs. Both offer app control and a color-coded display.
$269 and $79; AirThings
Factors That Increase Indoor Air Pollution
What could be polluting your air—and what to do about it
|CONTAMINANT||POTENTIAL SOURCES||HOW TO LIMIT EXPOSURE|
|Carbon monoxide||Home heating equipment, gas cooking appliances, cars in attached garages, fireplaces||Vent sources directly outdoors; check the operation of appliances; seal cracks between your garage and home. Install CO detectors to alert you to unsafe levels.|
|Nitrogen dioxide||Home heating equipment, gas cooking appliances, cars in attached garages, fireplaces||Vent sources directly outdoors; check the operation of appliances; seal cracks between your garage and home.|
|Volatile organic compounds (VOCs)||Cleaning products, building materials, paints, solvents, wood preservatives, fuels, aerosols, air fresheners, pesticides, dry-cleaning fluid, scented candles, printer ink, adhesives||Ventilate. Look for no-VOC paints, building materials, and cleaning products; urea formaldehyde-free furnishings; and certification seals from Greenguard, Green Seal, and Green Label Plus. Let items (dry cleaning, too) off-gas before they come inside.|
|Particulate matter||Smoking, wood-burning fireplaces, woodstoves, household dust, pollen||Vent all combustion appliances directly outside; don’t smoke indoors; have a pro inspect and clean flues and home heating equipment annually; change filters on HVAC systems when dirty, or at least every six months.|
|Biological pollutants||Areas with food debris and moist humidity, such as kitchens and baths; dust; pets; insects and other household pests||Ventilate to remove moist air; eliminate plumbing and foundation leaks; remove shoes at the door; keep your house clean and free of pests.|
|Asbestos||Roofing and siding shingles, pipe coatings, vermiculite insulation, some vinyl flooring and adhesives, fire-resistant materials||Intact asbestos can be left alone; if the material is damaged or might be affected by a remodel, call in a professional for an assessment.|
|Lead||Aging paint and the dust it produces as it degrades; contaminated soil||Test for lead paint before remodeling; never sand, scrape, or use a heat gun to remove lead paint. If intact, lead paint can be encapsulated by painting over it. For large-scale removal, call in an EPA-certified Lead-Safe pro.|
|Radon||Cracks in basements and foundations can provide a pathway into the house, as can water supply lines||Test when you move into a house, and after any renovation that disturbs the surrounding soil. Some experts suggest testing every few years. Install a radon mitigation system if warranted.|
|CONTAMINANT||POTENTIAL SOURCES||HOW TO LIMIT EXPOSURE|