Indoor Air Quality
There’s nothing more important than the air you breathe. From the experts:
- Given a choice between air quality and saving energy, top priority goes to indoor air quality every time. Especially if you have allergies—and if you don’t want to get allergies!
- Use volatile compounds outside or in a well-ventilated area.
- Designate your home as a no-smoking area. Send smokers outside!
- Every time you open the door of your wood-burning stove, a plume of smoke escapes into the house. It dirties the white ceiling and clogs up the HVAC air filter.
- Wrapping a house with one-inch rigid foam insulation panels (1) reduces air infiltration (tape the seams), (2) reduces thermal bridging (covers up the studs), (3) increases the overall R-value of the wall assembly, and (4) improves resistant to moisture and water penetration.
- Change the HVAC air filter regularly, especially after it gets a brownish, yellow color. The vacuum, clothes washer, and kitchen-stove vent have filters than need changing, too.
- High-efficiency air filters extract smaller particles from the air.
HEPA filters are the ultimate, but the increased static air pressure can burn out the HVAC fan motor. Consult your contractor for advice.
My house was surrounded by smoke for two months because of wildfires one summer. I bought a couple of air purifiers with giant, heavy-duty filters to keep the air inside my home (reasonably) clean.
Keep rugs and carpets clean, especially if there’s a shedding pet in the household.
Dust, dander, and mold accumulate in air-supply ducts after many years of service. An AC contractor can scrub them clean.
Rugs and carpets are a kind of filter, trapping particles and dust. Clean them regularly, and they’ll keep your house clean, too.
Moist, humid air breeds mold and allergens. Control the indoor humidity with a dehumidifier and avoid those problematic issues.
Houseplants pull contaminants out of the air: small ferns and lilies are good, and larger plants like palm trees, too. Bamboo, ivy—a palm tree! How dramatic is that?
Shoes collect dirt, pesticides, and other pollutants. Leave them at the front door or outside on the front porch.
Vacuum carpet and rugs regularly. (Some vacuums have HEPA filters.) Mop vinyl, hardwood, and tile floors.
Choose “Low VOC” and “Zero VOC” (Volatile Organic Compounds) paints when remodeling.
A humidifier in the winter can keep the indoor humidity at the ideal 30 to 50 percent.
Purchase fragrance-free cleaning products, laundry detergent, and soaps.
Replace aerosol sprays with non-aerosol products.
Beeswax candles emit almost no smoke and can make your house feel very cozy. Test your house for Radon, a cancer-causing gas present in almost any soil. Radon seeps through the foundation and into the house.
Nix mold and mildew when you find it—in shower walls, under the kitchen sink, in any damp, dark location. If the problem persists, look for a water leak and fix it!
Air leakage reduces the R-value of insulation in the roof, walls, and ceiling.
Leaking air moves moisture and pollutants into and out of the house.
In a strong wind, air leakage by the stack effect causes abnormal pressures on the leeward and windward exposures, interfering with the proper venting of combustion appliances. (Products of combustion can remain inside the building envelope.)
The wood stove should have outdoor combustion air vented to the unit, especially for tight-house construction.
Get rid of unvented space heaters (don’t even donate them to charity because that would be a disservice), which vent all the products of combustion into the house.
Move paints, cleaning fluids, and all volatile chemicals outside the conditioned space.
Vapor barriers don’t do much good for areas of the building envelope with the worst air leaks: window and doorframes.
Clean bedding, drapes, and other items that collect dust at least every spring (more frequently if you have indoor pets).
If you have allergy issues but can’t bear to live without Fido the dog or Oscar the cat, an air purifier may help. Activated charcoal works very well.
Use the stove vent fan to get smoke and fumes out of the kitchen before they get into the house proper.
Cold, dry winter months are a great time to throw open the windows for an hour in the afternoon to air out the house.
Some furniture has toxins that seep into your home sight unseen. Furniture made with particleboard is especially bad. (Toxin glues are used to bind the sawdust together.)
Gaskets that fit behind outlet and light-switch plates form an effective air seal.
Replace worn door-bottom and threshold gaskets with new, pliable seals.
A single-glazed window in a cold climate covered by a storm window (doubling the insulation value) can save upwards of a gallon of heating oil per square foot of window area (per heating season).
A leaky wood window can be refurbished with weatherstripping. A well-sealed window can lower the unit’s heating and cooling load by half.
If you never open a window, seal it tight with rope caulk and lock it closed with the window-latch hardware.
Exterior storm windows in the Frost Belt can reduce heat loss through the window assembly by 20 to 40 percent and air leakage by 70 percent. Interior storm windows perform even better.
A quality, airtight storm window (airtight = no condensation in the air space) has a better R-value than a premium, new window system.
I’ll list the standard ways to seal the exterior shell of a house, but I don’t recommend extreme diligence. A somewhat leaky house is okay but not so much a swiss-cheese house.
The impetus for an airtight house is that, according to the tight-house gurus,
“the outer shell of a house can account for 30 percent of your heating and cooling bill.” They don’t explain that half of that 30 percent is because of heat conducted through the shell.
17.1 A SECURE BUILDING SHELL IS ESSENTIAL, BUT THERE ARE MITIGATING CIRCUMSTANCES:
Older houses can have a significant infiltration problem. Newer construction, especially custom houses, are less problematic.
Leaky shells are a victim of wind. If trees all around your house block the wind to a certain extent, that’s good.
Do you live in a pleasant climate and open the windows a lot? That diminishes the return on the time and attention spent sealing the shell.
Are there smokers in the house? And you still want to seal it airtight?
Do you have kids (teenagers, adults!) who are in and out a lot? Or pets, with their private pet door? The more activity, the less benefit you get from a sealed house.
17.2 A FEW CONSIDERATIONS IN FAVOR OF THE SEALED–HOUSE PARADIGM:
Bug, termites, centipedes: Got cracks? We’ll go there.
High outside humidity (Gulf Coast states or the eastern half of the United States in the summer) is a mortal threat to any house because moisture can bring havoc into your home sweet home: rotting wood, mold, condensation on uninsulated cold water pipes.
A cold climate with strong winter winds? Do you have freezing air whistling through cracks in the walls and around the doors and windows all night long? Grab your caulk gun and get to work!
Generally, the older the house, the greater the benefit of sealing cracks and openings.
While you’re at it, investigate every opening before you fill it with caulk or foam. Is there insulation in the walls? How much and what type? Is the electrical wiring in good shape? The plumbing? Wood framing?
Outside walls – on foot
There are two sides to the exterior walls, each of which has its unique air-leak solutions. We’ll start with the outside.
17.3
Top priority goes to surfaces perpendicular to the wind: the outside walls.
17.4
Is the base plate between the slab and the framing exposed? You’ll see a long perpendicular crack just above the concrete around the whole perimeter of the house. Overhanging siding should already cover it. If it isn’t covered, well, as visible as that area is, consult with a contractor for the best way to seal it.
17.5
Electrical (outlets) and plumbing (faucets) penetrations are easy to access. Seal small cracks with caulk and large spaces with expanding foam.
17.6
Ground-floor windows and doors should be accessible. Check for cracks and openings around the wood frame-ins, and caulk as needed.
17.7
Seal cracks in wood and siding ASAP because water seepage into the wall can cause rot and more.
The roof – careful!
17.8
Problem areas are flashing around the chimney and where an upper floor might rise above a roof layer.
17.9
Use asphalt-based products (comes in tubes for a caulk gun) to seal any apparent openings around the chimney and vertical pipe penetrations (those are plumbing vents for the sanitary waste system).
17.10
Again, water-tightness is critical, and any flaws in the roof system are a five-star priority. Water stains in the attic might give additional clues to problem leaks.
Crawl space
If you have a ventilated crawl space; well, not much wind happens there, but lots of critters have free access.
17.11
Seal around piping and electrical penetrations. Go there at night with the lights on inside the house to look for pinholes of light shining thought the floor. Instead of caulking them at night, mark each area with spray-paint and do the repairs during the day.
Outside again – with a ladder
17.12
Caulk and seal the corners where the walls meet the roof overhang, against possible water-infiltration from wind-blown rain. Gulf Coast houses get condensation and moisture on the walls and overhangs; you’ll see mold or dirtiness where water tends to collect.
17.13
Caulk four-by-six foot panel siding and vertical plank siding along all vertical seams. The siding contractor should have done that when they built the house. Check those seams and look for any cracks in the wood. Caulk and then paint to match.
17.14
Every crack, hole, open seam, and penetration—anywhere water can get in, either blown by the wind or flowing down the side of the walls. Seal it tight for waterproofing.
17.15
A couple of coats of good, quality exterior paint is an excellent overall finish for the shell, both for water protection and air infiltration.
17.16
If you’re new to this whole siding thing, the basic idea is: If there used to be caulk in an area and if it’s either gone, cracked, damaged, brittle, or rotten, replace it with a bead of fresh, new, elastic exterior-rated caulk.
17.17
Once you’ve resolved all these issues, the house is now back to its original state. It’s not an “airtight” house by modern standards, but it is “watertight.”
17.18
If you see tons of problems and your house needs a fresh coat of paint anyway, I recommend leaving it all the painters. Just be sure you show them all the problem areas you found, so they do a thorough job. And don’t go skimping on paint; use two coats of high-quality name-brand paint.
Inside the house
Just as the critical exterior-half-of-the-shell problems were water-related, the significant interior-shell problems are insulation-related.
17.19
Pull off a couple of electrical outlets and light switches. Investigate the space around the electrical box. If there’s no fiberglass or other insulation in evidence, your walls don’t have insulation. Big problem!
17.20
Fill gaps around each electrical junction box with expanding foam. The insulation contractor should have done this when they built the house. A hole like that in the thermal insulating layer degrades the R-value of the whole wall assembly.
17.21
If one or two outlet boxes need foam insulation, it’s a safe bet that they all do. So, go ahead and check all the outlets on the outside walls and top off the insulation as needed.
17.22
If any plumbing runs are accessible, under sinks or in closets, add spray foam around the pipes to fill any voids to keep the bugs out.
Attic
Find your way into the attic. Clear insulation off recessed ceiling fixtures. Those lights create a lot of heat. That heat has to escape, or the bulb will burn out, or the wires short.
17.23
If you can reach where the chimney goes through the attic space, seal any problem areas at the roof in that area. Use asphalt-base caulk to seal possible water penetrations. Don’t put any insulation within a few inches of any surface that might get hot.
17.24
Don’t seal any areas in the walls because the attic needs ventilation for moisture control.
BACK INSIDE THE HOUSE—WITH A LADDER
17.25 The painters should have sealed ceiling and floor moldings along the wall and ceiling with a bead of caulk. That caulk also completes the air-tightness of the interior walls.
17.26
Gypboard wall seams were “taped” and covered with “mud” during construction, so the overall wall assembly is airtight, including corners.
17.27
The best way to seal windows is to lock them closed with the latch hardware. Visually check caulking around wood window framing to be sure it’s viable. Likewise, with the wood framing around the interior of outside-opening doors.
These are all essential maintenance tasks. They complete the thermal envelope of the house and reinforce the vapor barrier and water integrity of the outside walls.
17.28 TECHNICAL ISSUES THAT ARISE FROM A WELL–SEALED SHELL.
Home energy books present a “tight” house as an energy-saving panacea. It’s important to reduce infiltration, and doing so does save heating and cooling energy. Large openings in the outer shell are unacceptable and must be repaired ASAP. However, issues with water-penetration and flaws in the uniformity of insulation coverage, notwithstanding, “tightness” has its limits of practicality.
Let’s assume a well-sealed house: taped seams on the outside wall underlayment, uniformly caulked everything, foam-sealed service penetrations—the whole shebang. A contractor’s whole-house blower test comes out “tight as can be.”
Now, put a family of four, a dog, and a cat inside that sealed bubble. They consume oxygen and exhale carbon dioxide—active children and exercising adults even more so. Pretty soon, the available oxygen inside the house is used up and replaced by carbon dioxide.
What’s the conventional solution? Force-feed outside air into the house at the AC unit, usually via a small fan interlocked with the air handler. Except, that extra air pressurizes the house, so now you need several new penetrations so air can escape, to equalize pressure with the outside.
After spending all that time, money, and expense to seal the house completely airtight, you now must punch several large holes in the building shell! Moreover, the AC now has to cool down that outside air (heat it in the winter), just like with infiltrated air through a “leaky” shell. Overall, you still lose a large volume of conditioned air to exfiltration.
Fortunately, the air-exchange volume is probably less than with a typical “nottight” house. Although, you now have an additional energy load: an outside air fan.
Now, what happens if you have a gas stove, which gobbles volumes of oxygen from the air to fuel the combustion process? A gas clothes dryer? A roaring fire in the hearth?
Oh, we can fix that, too: Install a CO2 sensor to run the outside-air fan continuously when there’s a peak in oxygen demand. Electronic controls are required, too, to interlock the CO2 sensor and the fan motor. Add a small programmable motherboard to make it all work.
For a large house with a high occupancy and several combustion devices, you might even need a “Heat Recovery Device” (HRD). This appliance takes energy from the exhausting volume of air and uses it to temper the incoming air. That HRD requires extra ductwork, more sensors, and additional control interlocks.
Do you see why contractors are so gung-ho on “tight houses?” Lots of extra high-dollar equipment and regular trouble calls to maintain it for years hence.
Hey, I’m a mechanical engineer. I love all that technology. But I’d never put it in my own home. That kind of elaborate tech has its place: in large, commercial buildings where the air volumes are much more significant, the fans larger, and the controls more robust.
I like simple. Simple can’t go wrong. What happens when the power goes out for a few days or weeks? What if the ventilation fan or the CO2 sensor fails, and the indoor air quality slowly deteriorates? (You’ll never notice the change; it’s like a silent, lethal killer stalking you.) Oxygen deprivation is a severe condition, i.e., “mountain sickness” suffered by people who go to high altitudes without prior acclimation. Its symptoms include mental confusion, lack of affect, low attention span, all the way up to psychosis, and Attention Deficit Disorder.
Let me put it this way: Will your contractor sign a legal document accepting liability if bad things happen because their air-quality system failed? Giant commercial consulting and construction firms offer no such indemnity. You can be sure no residential contractor will, either.
Sealed house? Great in theory, but it’s not for your average middle-class household.
17.29 A SEALED HOUSE ON A COLD WINTER DAY.
The building envelope of a warm house on a cold winter day is like a hot-air balloon. Hot air tries to rise, and the colder it gets outside, the greater the impetus to rise.
That “thermodynamic pressure” is a physical force that pushes warm house air out of every conceivable opening, especially those in the ceiling of the top floor. That’s why it’s so important to seal any crack or opening from inside the house and also from inside the attic.
Future Tech!
17.30
Ideally, every house should be pressure-tested to determine how tight the construction is. 95 percent of houses are probably okay. The other 5 percent, however, aren’t getting sufficient oxygen.
17.31
A “blower test” can be done with any HVAC upgrade or other major project done on the building envelope.
17.32
All new houses need to be pressure tested. If the structure is too tight, outside air must be ducted into the house via a dedicated fan, and monitored via a CO2 sensor.
17.33
Home security systems should upgrade all their properties to have CO2 sensors and alarms.
17.34
Long-term, the only way to make indoor air quality standards work at either the residential or commercial level is to have legal penalties and liability for malfeasance by contractors, architects, builders, and engineers.