Building for Better Breathing

Bruce Davis teaches the basics of building science.

Figure 1. For many particles, a pleated paper filter is as good as an electrostatic precipitator. It's also more dependable. And almost anything is more effective than the furnace filters that come standard on most units. We chose simple pleated paper filters for our home.

The simple, energy-efficient design and low-cost features of our home, plus a state-of-the-art ventilation system, means we have the cleanest air possible while keeping energy costs low.

When my family and I had our home built here in North Carolina, good ventilation and air filtration were top priorities because my daughter has problems with allergies and asthma. We considered occupant health and comfort, combustion safety, building and equipment durability, and energy efficiency. Before construction began, we made simple but important decisions concerning siting, foundation, framing, insulation, exterior surfaces, and heating and cooling systems. We figured that high-quality air filtration and ventilation systems would add very little to our installation and operation costs. And we were right.

Simplicity for Savings

The simple design also made it easier to build a continuous air barrier and insulation layer. The home has R-30 insulation in the ceiling, R-19 in the walls, and R-22 in the floors (the local code requirements are R-30, R-13, and R-19, respectively). I made sure the insulation was properly installed for maximum effectiveness; that is, the material was installed in all the right places, was not compressed anywhere, and was continuous-there were no gaps.

The windows we chose are simple, too. They are moderately priced, with separated metal frames and plain double-glazed glass. The doors are foamcore steel with double-glazed windows. I feel that you don't have to have some kind of "magic windows" that cost a lot in order to have comfort and efficiency.

To promote durability and avoid moisture problems, we made sure that the crawlspace was sealed and that vapor-retarding plastic sheeting was used to completely cover the crawlspace floor and walls (see "Educating Builders, Updating Codes," HE Mar/Apr '98, p. 35). We put plastic sheeting under the pier footers and sealed it to the rest of the ground cover to keep moisture from wicking up through the concrete.

The Heat Is On-Low

Testing the Contractor

Typically, I would request a room-by-room load Manual J calculation, and system specifications based on those results; I would get references; and I would ask what kind of tests the contractor does. At the minimum, they should perform Duct Blaster and blower door tests. It is essential that they use mastic to seal the ducts. I would also find out what kinds of ongoing training they and their crew have had, what they do for quality control, and what kind of guarantee they would agree to.

By choosing the right HVAC contractor, I ensured that the duct system was correctly designed for my house and was installed to be airtight. After installation, Design Aire owner Jack Orum and I pressure-tested the system with a duct blower to confirm that it did not leak-at all. After the air filters were in place, we measured and properly adjusted the total system air. We made sure the refrigerant charge for the heat pump was accurately calculated, measured, and installed, and that the air flow to each room was measured and balanced. We provided return air-flow paths from each room back to the central return, with code-compliant door undercuts; and we installed an extra return register and duct in the master bedroom so that, when the bedroom door is closed, the house would still be pressure balanced.

Filter for Life

I used 2-inch paper-media pleated filters in each return grille; these offer a tremendous increase in filtering ability for just a few dollars (see Figure 1). I need to change them every three months. I also installed a special 6-inch pleated Space Gard filter at the heat pump air handler located in the crawlspace. These filters are changed once each year and cost about $17 each; they have pores small enough to trap 65%Ð90% of most pollen, mold spores, animal dander, and hair, and even do a good job of removing airborne fibers, skin flakes, and some bacteria. Their pleated design yields much greater surface area than a flat filter, allowing less resistance to air flow and a longer useful life. Plus, they're easier to maintain. Some other types of filter, such as electrostatic precipitator (ESP) filters, require continuous maintenance in order to work well. If they lose their charge and stop filtering, you may not know it for weeks-by then, your coil is dirty. In contrast, the 6-inch pleated filter has a good efficiency rating and is simple. Note that every extra filter adds static pressure drop, and the system must be designed with that in mind.

Let It Flow

To ensure proper ventilation of my home, I installed a balanced mechanical ventilation system that provides filtered outdoor air to each room in the house, continually removing stale, contaminated air at the same rate. It operates 24 hours per day, removing pollutants that are released from construction materials, household chemicals, and the like. The particular ventilation system I installed is an energy recovery ventilator (ERV) made by Honeywell, the ER200-ERV. This one cost about $1,000 installed (including ductwork and controls), but other ERVs run from $600 to $2,000. Its installation as a separate system with simple direct ducting did not interrupt the construction schedule. It used 1,157 kWh in the first year. This type of ventilator is designed to strip out much of the moisture and heat from the incoming air during the summer and transfer it to the exhaust air, thus reducing the load on the conditioning system. During the winter, the ERV retains much of the moisture and heat that would otherwise be exhausted with the stale outgoing air. And since equal amounts of exhaust and supply air are going out and coming in all the time, the air pressure in the house is neutral with reference to the outside, meaning the house is neither sucking air in nor blowing it out. With this balanced ventilation system in operation, we breathe fresh outdoor air all year long. We avoid the unpleasant and often unhealthy "new house" smells that come from outgassing chemicals.

Another simple step I took to improve ventilation was to be sure that the ducts from the standard exhaust fans in both bathrooms and from the exhaust hood over the kitchen range were all tight and ran smoothly to the outdoors.

The Devil Is in the Materials

To avoid the pollution and safety issues surrounding combustion appliances, I chose an all-electric heating and cooking design. This eliminates any combustion by-products from the air (unless you burn your food) and greatly reduces the associated fire hazards.

I Bought What I Taught

We love our new home. It's the most comfortable house we've ever lived in or visited. Even though it is fairly ordinary, it has no drafts, excessive humidity, high energy bills, odors, noises, or hot and cold spots. Instead, what we have is an energy-efficient and extremely comfortable home.

My daughter feels her home is a haven to retreat into when her allergies to everything in the outside world are causing her problems. This means that her stress levels are lower, and because she is less exposed to allergens, her sensitivity levels are a bit lower as well. She says the only bad thing about the house being so tight is that she can't hear the rain on the roof.

Bruce Davis is a building science specialist with Advanced Energy's Applied Building Science Center in Raleigh, North Carolina.

Home Energy can be reached at: contact@homeenergy.org
Home Energy magazine -- Please read our Copyright Notice