HRVs, ERVs, high-velocity systems and ductless mini-splits…
…the use of these modern HVAC systems is growing exponentially in homes across the country. It’s important that air ventilation systems work correctly to ensure good air quality. Do you know the basics about these systems, including what to look for and point out to clients when you encounter them?
We asked three experts to put themselves in a home inspector’s shoes and describe important aspects of these mechanical systems that are becoming more and more common in energy- efficient homes.
Paul Raymer specializes in HRVs/ERVs and authored the book Residential Ventilation Handbook: Ventilation to Improve Indoor Air Quality. He emphasized the idea that a house is a system in which every part relates to every other part.
HRVs use the heat in outgoing stale air to warm the fresh air coming into a home. Typically, HRVs use one fan with two wheels (one removes household air and one brings in fresh air) and a heat- exchange core that transfers heat from the outgoing to the incoming airstream. The core’s narrow alternating passages for the airstreams allow it to transfer heat from the warm side of each passage to the cold, without mixing them.1
“HRVs are ideal for tight, moisture-prone homes because, in the heating season, they replace the humid air with dry, fresh air. In climates with excessive outdoor humidity, an energy-recovery ventilator is more suitable. This device is similar to an HRV, but dehumidifies the incoming fresh airstream.”1
Raymer said, “With newer, superinsulated homes, internal comfort may be achieved through effective ventilation systems.” He suggested that, when inspectors see a home’s mechanicals, they should note whether the BTUs of the furnace are lower than what is considered normal. And if an ERV is in place, ask this question: “Are these systems working in tandem?” ERVs can often reduce the necessary tonnage of the furnace by lowering the moisture that might be drawn into the home.
Raymer said, “Balance is the key factor of HRVs/ERVs. I see more oversized than undersized A/Cs. Oversized A/Cs often have an excessive electric load. For example, if there’s a window A/C unit installed in the master bedroom, this tells me that the home may have an oversized A/C unit that’s short-cycling, which means that it’s not running long enough to effectively dehumidify the air. Sometimes you’ll see a 5-ton A/C in a house that should have a 2-ton A/C.”
Codes and resources. Look for documentation on the HRV/ERV unit (or ask for it if it is not clearly marked on the unit). The International Energy Conservation Code (the model energy code) requires whole-house mechanical ventilation, in addition to bathroom ventilation. American Society of Heating, Refrigerating and Air- Conditioning Engineers (ASHRAE) Standard 62.2 is the ventilation standard for low-rise residential buildings in the United States that requires ventilation performance to be tested. (Refer to www.ashrae.org for more information.)
The Air Conditioning Contractors of America (www.acca.org) provides various quality-related resources about HRV/ERV standards, installation, maintenance and restoration that could be useful for home inspectors and their clients.
Duct systems. Ventilation—not cooling or heating—is the purpose of an HRV/ERV. These systems ideally have a dedicated duct system, so in addition to the ducts used for heating and cooling, there should be another set of ducts for ventilation. If an HRV has its own duct system, it can be balanced, but if it’s connected to an air handler, it can be unbalanced when the air handler is operating. Raymer cautioned inspectors to be aware that an HRV/ERV can tap into either input or output ducts, but if the HRV/ERV is tapped into both of these, the performance of the HRV may be useless.
The goal is to achieve efficiency and balance. An unbalanced HRV/ERV is either bringing in or putting out unequal amounts of air. An HRV/ERV can’t be balanced if it’s using both supply and return. HRVs are, by design, balanced systems, but they do not add air to the house—an HRV only brings in an equal amount to what is expelled.
Indoor units. Accessible placement of the HRV/ERV unit is critical. If it’s difficult to reach the unit, it will be difficult for the homeowner to check and maintain it. Inspectors can check the flow tabs on the sides of the HRV unit; these can help with balancing the system for HERS ratings and/or energy audits.
An unbalanced HRV/ERV can put the house under negative pressure, causing an atmospherically vented combustion appliance to spill exhaust gases into the house.
Raymer has seen HRVs/ERVs in which the filters had never been replaced. To address this, open the unit to check that the filter is inside and note the state of the filter as well as the condition of the exchanger core.
Open the HRV/ERV cabinet to see if it has been maintained. If the core is not clean or if the cabinet is full of leaves, nests or other debris, then the core is drawing in unclean air and distributing that throughout the home.
HRVs have defrost cycles to melt ice on their cores. The internal drain pan should be clear of debris.
Outdoor units (exterior hoods). Inspectors can do a simple test with a garbage bag to determine how well the HRV outdoor unit is working. Check out the online factsheet2 for step-by-step instructions.
Exterior hoods should be 10 feet apart so that air doesn’t mix and contribute to cross-contamination.
Appliances. Check whether the intake and exhaust vents of range hoods or clothes dryers are clear and appear to have been installed and maintained properly. If an HRV or ERV has not been properly balanced, it can cause problems with appliances that use the chimney flue.
Shawn Intagliata is a great source of information about small-duct, high-velocity systems. Unico, his family’s business, produces an architecturally friendly, sustainable HVAC system.
Intagliata emphasized that home inspectors should understand the basic principles and the history of building science. He said, “The green industry is pushing the understanding of the building concept and the science behind it. The more knowledge that home inspectors have, the better they can help their clients understand details about their significant purchase.”
This primer of high-velocity systems is based on the Unico system: Unico’s ductwork is one-quarter the size of conventional ducts and is virtually leak-free. The system can be designed to work with multiple levels or ceiling heights and produces optimum indoor moisture management, which is critical in tight thermal envelopes. Its motor technology is software- driven, which guarantees delivered CFM of air to all space, and the system delivers an even temperature (within 2 degrees) throughout the space.
Unico systems have been installed in one of the largest affordable LEED platinum projects in the nation: Make It Right Foundation’s redevelopment project in the Lower 9th Ward of New Orleans, LA. This partnership has provided cooling and heating for 1,440-square-feet homes for an average cost of $0.68 per day.
High-velocity systems may become more prevalent in homes, owing to their optimum heat transfer and affordability. Because the ducts are much smaller than standard options, high-velocity systems can be found in metropolitan areas, custom homes and high-performance buildings. In the Northeast, they pop up in retrofits. They are also prevalent in Texas and in cities like Denver and New Orleans.
Intagliata said, “It’s a myth that a house can be ‘too tight.’ I’d argue that the house is mechanically mismanaged. If mechanical systems are working properly, then the house should not be too tight.” Having high-quality indoor air reduces the risk for mold and allergens.
“Selling agents may hope that an inspector’s report will indicate that everything’s perfect about a house,” Intagliata said, “but home inspectors know they have a responsibility to give accurate information that can affect the cost and value of the home. When reporting about HVAC systems, inspectors could make an effort to provide their clients with information that could increase their knowledge base about their purchase and to reach for better outcomes.”
Intagliata recommends that inspectors use these strategies with high-velocity systems:
- Detect whether there’s an even comfort level of conditioned air; in other words, it should be hot and cold in appropriate places.
- Check whether the outdoor unit is working properly; pay attention to the amount of leaves or debris and the way the unit sits on its base.
- Turn on the high-velocity unit to be sure it flows hot and cold. Check the filter placement and status.
- Turn on the fan and listen. A noisy fan could indicate an undersized system that lacks appropriate air flow or it could indicate that the system was not installed properly.
- If the house has an attic that sits above a living space, determine whether it appears to be reasonably sealed. Check whether there is a secondary drain pan under the unit and that the drain line slopes out.
- Check the indoor coil; it should be clean.
- Pull out the blower wheel; it should be clean. Blower wheels can become dusty; even 1/8 inch of dust can denigrate the motor’s efficiency by up to 20%.
- Look at the coil from the outside. If there is a top discharge, check inside the cabinet to make sure there’s no buildup of debris and dust. On the condensing unit, the compressor—the copper coil—dissipates heat outdoors. The copper coil, which can be cleaned with water, should be free of debris and dirt.
- Check whether air is flowing from every outlet. For example, if there are three outlets in one room but only two are blowing air, this could signal a shoddy duct split.
- Understand Energy Star levels. (Look for an article addressing this topic in the May issue of the ASHI Reporter.)
- Empower your clients by sharing information. For example, when inspecting an older home that lacks modern mechanicals, consider suggesting that the buyer invest in a high-velocity, small-duct system to better manage indoor relative humidity.
Ductless Mini-Splits A conversation with Ken Nelson, Northwest Regional Manager, Panasonic Eco Solutions – North America, Olympia, WA ( firstname.lastname@example.org, www.business.panasonic.com/products-hvac- ventilationproducts)
According to the U.S. Department of Energy (DOE),3 ductless, mini-split system heat pumps and air conditioners (often simply referred to as “mini-splits”) are becoming more common in multifamily housing. These units can be good retrofit add-ons to houses with “non-ducted” heating systems, such as hydronic (hot water heat), radiant panels and space heaters (wood, kerosene or propane). Mini-splits might be found in additions where extending or installing distribution ductwork isn’t feasible and in efficiently built new homes requiring only a small space conditioning system. The DOE recommends using Energy Star-compliant units and getting an experienced technician to install the system.
When describing the affordability and efficiency of ductless systems Ken Nelson explained that in a 2,000-square-foot house, for example, you could feasibly add a ductless mini-split heat pump as a supplement to a gas furnace and during the winter months, the home’s combined energy costs could drop by approximately $100 per month. This overall savings likely would involve a decrease in gas costs and an increase in electric costs.
Nelson noted that, although many builders typically install traditional HVAC systems, many buyers are looking for a more efficient zonal approach to heating and cooling indoor air, and this is particularly true where he lives in the Pacific Northwest. Ductless systems fit nicely with this choice. He said, “In my own home, I have two ductless mini-split register heads—one in the great room and the other in the master bedroom. The units bookend the house, pointing toward each other, and by providing heat zonally, they require less than 2 tons of heating/cooling energy on even our coldest days.”
He explained that ductless systems work to continually rotate the air. Nelson said, “Overall, operational costs are low. In some cases, for about $1 of energy costs put in, a system might put out about $5 worth of heat. Ductless systems are remarkably efficient, with the primary reason being that the heating and cooling functions only occur inside the conditioned space of the home.”
Ductless heat pumps consist of an outdoor condensing unit connected to an indoor wall (or ceiling) register head. Outdoor and indoor units are connected by a line set (a gas line and a fluid line), control wiring and a small condensate hose that drains potential moisture from the indoor unit outside the house. Condensation can occur when the ductless heat pump is in the air-conditioning mode.
Nelson described that, ideally, a ductless wall unit should be placed on an exterior wall mount with a condensate drain line at one end; in this way, gravity helps pull the moisture down and away. Ductless units can be placed on interior walls, but there is a risk that condensation could become an issue so these units may need a condensate pump. Some ductless units are designed in a “cassette” style and have their own condensate pumps.
Concealed short-run ducts also are beginning to be installed in some new construction. Functioning like forced-air units, these systems can be “hidden” in the upper sections of compact spaces such as closets or bathrooms. Nelson offered these suggestions for inspectors who encounter ductless mini-splits:
- Open the register head and observe the status of the filters. Filters should be cleaned periodically to enhance the unit’s efficiency and ensure clean air, and more often if there are instances of heavy pollen or other indoor air-quality issues.
- Find the condensate tray, which should be unclogged and free of bugs and debris. Trays should be routinely cleaned. The tubing should lead to a drain hose.
- On the indoor unit, turn on the fan and listen. The fan should run smoothly and without unnatural noises.
- Try out the remote control to be sure it works properly with the system.
- Consider using a thermometer to document the range of hot and cold temperatures that occurs when temperature adjustments are selected. Reduced temperature ranges can be an indicator of low refrigerant levels.
- Take note of temperature differences between rooms and communicate expectations to the client if they are unfamiliar with this type of system.
- Determine whether the outdoor condenser is raised above the ground and check that the area around the condenser is free of overgrown shrubs, pests and debris.
- Look for ice or damage to the condenser unit or blades; this could be a the result of ice buildup and may indicate a low refrigerant situation preventing the condenser from completing a proper defrost cycle.
Inside view of a Broan ERV S100. A solution for high-rise residential owners.
1. Klenk T. How it works: heat recovery ventilator. Popular Mechanics. July 31, 2000. www.popularmechanics.com/home/interior-projects/how-to/a149/1275121/. Accessed February 22, 2016.
2. Canada Mortgage and Housing Corporation. About your house: maintaining your heat recovery ventilator. Revised 2010. www.cmhc-schl.gc.ca/odpub/pdf/62043.pdf?lang=en%29. Accessed February 22, 2016.
3. U.S. Department of Energy. Ductless, mini-split heat pumps. (http://energy.gov/energysaver/ductless-mini-split-heat-pumps.) Ductless, mini-split air conditioners. (http://energy.gov/energysaver/ductless-mini-split-air-conditioners.) Accessed February 24, 2016.
Mike Collignon is the Executive Director of the Green Builder® Coalition, an organization he co-founded in 2010. He engages in national and state-level advocacy, co-produces quarterly research reports, and publishes a monthly member publication and a monthly feature in Green Builder® Magazine. He has presented at EEBA, RESNET, the Pacific Coast Builders Conference, Better Buildings: Better Business (Wisconsin), Green Building Focus, StormCon and the Sustainable Disaster Recovery Conference. Mike has also delivered testimony at the IECC and IgCC final action hearings. He also has served as the moderator for Green Builder® Media’s Impact Series webinars from 2012 to 2014, and became the host in 2015.