The regulator also can add humidity to the fresh air as needed to maintain an optimum level for comfort and health, using a rotary wheel core and desiccants such as silica gel. As a result, ERVs extend their value in terms of indoor air quality beyond simply refreshing the indoor air. The bit of moisture vapor captured by an ERV also helps keep the exchanger core warm, lessening the potential for freezing damage and related repair or replacement costs during the winter.
Cost vs. Value
At upwards of $1,500 or more plus some extra labor by a heating contractor in a new construction environment, ERVs and HRVs are a relatively expensive choice to provide controlled ventilation and some measure of energy efficiency, especially in affordable housing.
“If equipment prices and the cost of installation went down, we’d probably go back to using an HRV,” says Brianna Conrow, project manager at HOST Development in Portland, Ore., which used HRVs for the first phase of an affordable project before switching to a supply-air-only system of whole-house fans. “And in small homes, there’s not a reasonable payback in energy savings for HRVs.”
There’s also a remarkable shortage of hard evidence that mechanical ventilation, and specifically an ERV or HRV, is truly as effective as the presumed benefits of energy savings or improved indoor air quality that equipment manufacturers and building scientists purport. “It’s become a Holy Grail to ask for definitive research on the air quality impacts of [controlled] ventilation,” says Sam Rashkin, national director of the Energy Star for Homes program at the EPA, whose team has scoured for and requested reports from manufacturers and the building science community without success—despite pressure from those groups to add controlled ventilation into the Qualified Homes standard. “The evidence [that controlled, mechanical ventilation reduces indoor air quality hazards] is anecdotal, at best.”
In addition, Rashkin’s team found field reports and observations that HRV/ERV equipment showed a high propensity not to work properly once installed, from dampers being pinched shut to kinks in the ducting systems that restricted airflow and clogged or misplaced intakes.
It’s also a “big leap of faith,” he says, that homeowners will follow through with scheduled and necessary maintenance of the equipment. “We suspect that a high percentage of systems will be installed poorly or be set up to fail because the owners won’t do things necessary to keep them running properly,” he says. “Having a ventilation system is a feel-good thing, but there’s a tremendous behavioral component that’s hanging in the balance.”
That’s an assertion that Gentry, among others, disputes. In his experience, maintenance is an easy chore for a properly trained homeowner, consisting of cleaning the filters and blowing dust out of the system twice a year and out of the core (or heat exchanger) annually—which many owners simply add to an HVAC service contract. “Every once in a blue moon you may have to replace the heat exchanger,” he says, “but in four years of selling ERVs I’ve never had to.”
In addition, emerging technologies such as electronically commutated motors (ECMs), which use less energy and have been a standard in larger HVAC equipment for years, and controls that allow the installer and the homeowner to more easily and reliably program, monitor, and adjust the equipment, appear to address at least some of the current concerns.
Despite Rashkin’s reservations, he and his team resolved to mandate minimum ventilation thresholds into the upcoming Energy Star Qualified Homes standard, likely spurring HRV and ERV use, because the 2011 version significantly boosts building envelope performance. “The new  standard raises the bar so much higher for a home’s tightness that we have to get fresh air into them,” he says.
Rashkin also admits that, if properly installed and maintained, HRVs and ERVs are an upgrade over exhaust-only or supply-only systems because the air in and out of the equipment is balanced and therefore better ensures the proper amount of fresh-air flow and maintains a pressure balance inside the home.
As for the energy efficiency of HRVs and ERVs, Energy Star is working to create standards to qualify the heat recovery performance and label the equipment within a new product category for the federal program; the 2011 Qualified Homes ventilation thresholds will require Energy Star–labeled HRVs or ERVs to comply (if that ventilation option is chosen by the builder), just as the current standard does for exhaust-only (spot) ventilation units.
Already, the Home Ventilating Institute (HVI) independently certifies the performance of HRVs and ERVs to provide builders with a gauge to compare products and assess their value in terms of heat recovery and airflow rates, if not their impact on air quality.
Even so, HVI considers (if not certifies) the health benefits of controlled ventilation, including ERVs and HRVs, to be a critical factor in their use. “Even with construction materials … with low-VOC off-gassing, normal activities such as cooking and bathing overwhelm the home,” with potential pollutants that ERVs and HRVs can and do address, says Peter Grinbergs, the trade association’s chairman and the director of product development/engineering for Airia Brands, a ventilation equipment manufacturer.
For Gentry, that’s a theory he’s seen in action. “Getting fresh air into the house helps more than anything, and especially achieving healthy indoor air,” he says. “This isn’t smoke and mirrors.”
Rich Binsacca is a freelance writer in Boise, Idaho.