Install a ductless heat pump to provide heating and cooling to a single room or to an entire home:
- Determine whether a ductless system is more appropriate than a ducted system for your situation based on whether or not space is available for ductwork and a central air handler, the amount of area needing to be conditioned, zoning needs, ventilation system (fresh air) configuration, and performance specifications including cooling efficiency, heating efficiency, dehumidification performance, heating capacity at low outdoor temperatures (cold climate performance), indoor air filtration, and noise criteria.
- Perform ACCA Manual J heating and cooling load calculations for the space(s) to be conditioned by the heat pump.
- Determine number, type, and location of indoor units (heads).
- Determine number and location of outdoor units.
- Use ACCA Manual S methods to size and select a system with properly matched indoor and outdoor units. (If sizing the heat pump to provide heating in a cold climate, consider alternative methods to Manual S.)
- Assess the home’s electrical system and perform any upgrades needed to accommodate the heat pump and any auxiliary electric heating.
- Install the system including indoor unit(s), outdoor unit(s), refrigeration lines, condensate piping, electrical wiring, and thermostat control wiring and/or modules.
- Commission the system to ensure proper operation.
See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home program, ENERGY STAR Certified Homes, and Indoor airPLUS.
High-performance ductless heat pumps are an efficient alternative to traditional ducted heat pump systems, gas or oil furnaces, and electric resistance heating systems (Figure 1). Advances in technology in recent years have increased heat pump performance to the point that units are now available with heating efficiencies above 13 HSPF and cooling efficiencies above SEER 30.
Ductless heat pumps have been used in Asia and Europe since the 1970s and they comprise 80% to 90% of the residential HVAC market there. They have been used in U.S. commercial buildings since the 1980s and are now rapidly growing in the U.S. residential market.
Ductless vs. Traditional Ducted Heat Pumps
Ductless heat pump systems use the same basic heat pump technology as ducted systems, but the distribution of heating and cooling within the home is different. With a traditional ducted “central air” system, one centrally located air handler blows conditioned air through a system of ducts that deliver the air to individual rooms through registers (vents) in the floor, ceiling, or walls. The central air handler is usually located in an attic, crawlspace, basement, garage, or closet. With a ductless system, on the other hand, there is no central air handler or ductwork. Instead, small indoor units are installed inside the space they are heating and cooling. These indoor units are essentially small air handlers having a small fan that blows air directly into the space. Indoor units are often referred to as “heads” or as “fan coils.” The indoor units are usually hung on a wall or installed in a ceiling (Figures 2 and 3).
Ductless configurations allow better zoning and reduced fan energy consumption. Less fan energy is required because the units do not have to push air through ductwork. Ductless units allow zoned heating and cooling because each indoor unit operates independently of the others (Figure 4). In this way, different areas of the home can be set to different temperatures if desired. Some units can even be turned off while other units continue to heat or cool.
A major advantage of ductless systems when compared to ducted systems has to do with the potential heating and cooling losses through ductwork and the air handler. If a ducted system has the air handler and/or ducts located outside the conditioned space (for example, in a vented attic, vented crawlspace, or garage), heating and cooling losses will occur. It has been shown that losses related to duct systems can account for more than 30% of heating and cooling energy consumption if ducts are located in an unconditioned area. These losses occur through air leaks in the air handler and ducts, as well as through conduction of heat through the walls of the duct or air handler. With a ductless system, all of these losses are eliminated because the indoor units are located within the conditioned space. Ducted systems can eliminate these losses as well, however, simply by ensuring the air handler and all ducts are located within the thermal boundary (insulated walls, floors, and ceiling) of the home so that any heated or cooled air that leaks from the system simply goes into the conditioned space and no real losses occur. However, space constraints can make it difficult to locate all ductwork and the air handler inside.
Ductless systems also tend to differ from traditional ducted systems in terms of performance. In general, ductless systems tend to have higher cooling efficiencies, provide poorer dehumidification in cooling mode, and provide less air filtration. There are also currently (as of 2023) many more ductless models than traditional ducted models on the market that can provide reliable heating at very cold temperatures (referred to as “cold-climate heat pumps”). Some models can operate at an outdoor temperature of -15°F for heating and up to 115°F for cooling, eliminating the need for backup heat sources in many locations. It is important to note that all of these characteristics are simply general trends, and none of these aspects are inherent to ductless or ducted technology. Market trends change continually, and individual models should be compared with respect to all of these performance areas.
Ductless heat pumps generally have inverter-controlled, variable-speed compressors. Ducted systems can also have variable-speed compressors, but single-speed compressors are more common in these more traditional units. The variable speed inverter technology adjusts the compressor speed, allowing the system to adapt more smoothly to shifts in demand with less temperature variation and lower energy use. When maximum capacity is not needed, the compressor revolution and power decreases, increasing energy efficiency. In contrast, conventional single-stage air-conditioning and heating systems must stop and start repetitively. The inverter compressor allows the system to ramp down to as little as 10% of rated capacity (Figure 5). Ductless heat pumps and advanced ducted units also have linear expansion valves rather than open/close valves, and multi-speed rather than single-speed fans to continuously match the heating or cooling load. The capacity on a variable speed heat pump can have a wide range; for example, one ductless model reports a capacity range of 3,100 to 24,000 Btu/hr in heating mode and 3,800 to 14,500 Btu/hr in cooling mode.
Heat pumps and air conditioners have traditionally been relied upon for dehumidification as well as cooling. When providing cooling under typical conditions, these systems will automatically remove a certain amount of moisture from the air. A standard way to quantify how well a unit dehumidifies is called the Sensible Heat Ratio (SHR). SHR could theoretically range from 0 to 1, with lower values indicating better dehumidification performance. Heat pumps and air-conditioners have traditionally had SHRs of around 0.75. This has historically proven to provide sufficient dehumidification when the unit is properly sized and humidity conditions are not abnormal. Newer, more efficient units tend to have higher SHRs (worse dehumidification). This is particularly true for ductless systems. In homes where humidity may be an issue, a separate dehumidification system may be needed. See the Climate tab for more information.
For more information on refrigerant-based heating and cooling systems, see Traditional Split Heat Pumps and Mechanical Air-Conditioning.
Ductless System Configurations
The simplest ductless heat pumps consist of a single outdoor unit (containing the compressor, expansion valve, and coil) and an indoor fan coil (a “head”) (Figure 6). These one-to-one systems are often called “mini-splits”. The outdoor unit is mounted on an exterior wall or on a concrete, stone, or plastic composite pad outside the house; refrigerant tubing and control wiring connect the inside and outside units through a small hole in the wall.
Ductless heat pumps can be designed to provide heating and cooling to just one space such as an addition, a room that cannot easily be reached by ductwork, or an area that tends to get too cold in winter or overheat in summer. These systems would typically have only one indoor head (mini-split system). Ductless systems can serve an entire house as well. This typically requires more than one indoor head (“multi-split” system). It is generally not recommended to connect more than three indoor units to one outdoor unit, but some models allow as many as eight indoor units to connect to one outdoor unit.
Ductless heat pumps work well for use in small, very efficient homes with open floor plans or in larger well-insulated homes where zoned heating and cooling are desired. They also work well in additions. They can also be a beneficial part of an energy-efficient renovation where a less-efficient central heating system is kept in place for supplemental heating or cooling and one or more ductless heat pumps are installed in the primary living areas. Since interior space is not needed for bulky ductwork or air handlers, ductless systems are very convenient for retrofit applications.
Zoning can easily be accomplished by using multiple heads. Each head is individually controlled by its own wireless thermostat, which also communicates with the outdoor unit (Figure 7).
The three-zone ductless multi-split system in Figure 7 conditions the two bedrooms upstairs and the living room downstairs. While the system shown in this scenario could include additional ductless heads to condition the kitchen, the office, and the bathroom, these additional units would provide more capacity than is needed to condition the small spaces and the extra units would add considerably to the overall cost of the system. Another option, available from several manufacturers, is a ducted mini-split air handler with short ducts to provide conditioned air to several nearby rooms at once, such as bedrooms, bathrooms, offices, or storage rooms. The air handler is typically a horizontal unit, although some manufacturers make vertical units. The air handler has a larger blower motor to move air through the supply ducts and it also has a ducted return.
The ducted air handler is connected by refrigerant tubing to the outdoor unit along with any other ducted or ductless air handlers that are part of the system and, as with all of the indoor units, it must be verified that it matches the outdoor unit using the AHRI equipment matching system.
One outdoor unit may be able to accommodate a single ductless head, a single ducted air handler, multiple ductless heads, multiple ducted air handlers, or any combination of these (Figure 8). Verify capacity with the manufacturer for the models you are considering.
Some larger, commercial-scale heat pumps are variable refrigerant flow (VRF) systems. Variable refrigerant flow refers to the system's ability to control the amount of refrigerant flowing to each indoor fan coil. With VRF technology, one outdoor unit can be connected to different indoor fan coils (heads) that are heating or cooling in different zones. Some high-end systems can even provide heating to one zone while simultaneously providing cooling to another because they have an additional refrigerant line to each internal unit and a controller which directs them to pull heat from rooms calling for cooling and send it to rooms calling for heating rather than rejecting it to the outdoors. By moving the refrigerant from one zone to another, the system allows for some heat recovery. The multiple heads can be of differing capacities and configurations, providing for additional individualized comfort control.
Sizing and Selecting a Ductless Heat Pump
Correctly sizing the outdoor unit and each indoor unit (head) to the space loads is imperative for efficient and comfortable operation. Correctly locating the heads is also important for air delivery to the desired location. Oversized or incorrectly located air handlers can result in short cycling, which wastes energy and does not provide proper temperature or humidity control. A system that is too large will be more expensive to buy and operate.
Calculate the heating and cooling load for the home or space to be conditioned using the ACCA Manual J Residential Load Calculation. This calculation should be performed for individual zones (one per indoor unit) as well as for the entire house.
Properly size the equipment for the design heating or cooling load following the sizing guidelines in ACCA Manual S: Residential Equipment Selection. When determining equipment sizing per ACCA Manual S, use the original equipment manufacturer (OEM)’s expanded performance table to obtain performance data at design conditions, rather than using the performance data on the AHRI certificate, which lists heating and cooling capacity and SEER2 and EER2 cooling efficiencies at factory conditions of 95°F outdoor, 80°F indoor, and 67°F wet bulb.
If you are participating in an energy-efficiency program, select cooling equipment that complies with the requirements for your climate zone. To determine your climate zone, see the International Energy Conservation Code (IECC) 2021 climate zone map on the Climate tab.
Properly match the indoor and outdoor components of the heat pump system as demonstrated by a certificate from the Air Conditioning, Heating and Refrigeration Institute (AHRI). AHRI assigns a certification number and efficiency ratings to specific combinations of equipment (outdoor unit, indoor unit, indoor coil, fan type, etc.) that have been tested by the manufacturer according to AHRI test procedures using AHRI-specified test conditions (AHRI 210/240-2023). If an AHRI certificate is not available, a copy of the catalog data provided by the original equipment manufacturer (OEM) should be attached to the system indicating an acceptable combination and performance data.
Install the heat pump in accordance with the manufacturer’s instructions and relevant standards including ACCA Standard 5: HVAC Quality Installation Specification and ACCA’s Technician's Guide for Quality Installations and ACCA Standard 9: HVAC Quality Installation Verification Protocols.
How to Select and Install Ductless Heat Pumps
- Choose a system configuration based on homeowner needs. This includes determining whether to use ducted, ductless, or combination systems, how many zones and indoor heads are needed, the boundaries of each zone, and the location of each head.
- Calculate heating and cooling loads for each zone and for the entire home using ACCA Manual J. This is especially important if you have done significant air sealing and insulating, which will reduce your heating and cooling load.
- Size and select equipment using ACCA Manual S. When determining equipment sizing per ACCA Manual S, use the original equipment manufacturer (OEM)’s expanded performance table to obtain performance data at design conditions, rather than using the performance data on the AHRI certificate. For example, if the home is kept at 75°F and the outdoor design temperature for the location is 100°F, locate those columns on the performance table and match them to the design load.
- Choose the highest performing model project costs will allow, to meet the design heating and cooling load of the project. Take note of dehumidification performance as indicated by the sensible heat ratio (SHR) of the unit (lower SHR indicates better dehumidification during cooling). Note cooling efficiency (SEER2), heating efficiency (HSPF2), noise criteria, air filtration (higher MERV filters provide better filtration), and cold weather performance. If you are participating in an energy-efficiency program, select equipment that complies with the requirements for your climate zone.
- Determine whether a whole-house dehumidifier will be needed. If the selected heat pump has a high SHR, then additional dehumidification may be needed, particularly if located in a humid environment (Moisture Region A in the maps on the Climate Tab).
- Confirm that the indoor and outdoor components of the heat pump system match, as demonstrated by a certificate from the Air Conditioning, Heating and Refrigeration Institute (AHRI) or a copy of the catalog data provided by the original equipment manufacturer indicating an acceptable combination.
- During construction, keep the copper refrigerant tubing charged with dry nitrogen and sealed with solder to keep moisture out of the lines.
- After connecting the indoor unit and the outdoor unit, vacuum the lines to 500 microns to remove air pockets.
- Follow the manufacturer’s recommendations for refrigerant charging. Too much or too little refrigerant can reduce the efficiency of the equipment and lead to premature component failures. Use the charging method recommended by the manufacturer. There are three methods for charging: the subcooling method (typically for units with a thermal expansion valve), the superheat method (typically for units with a fixed orifice), or the weigh-in method (using the refrigerant weight amount listed on the data plate on the outdoor unit). Verify that you are using the correct method for the specific heat pump model to be installed. Refrigerant charging must be done by an EPA certified technician.
- Make sure the condensate line and drain pans are correctly installed.
- Test the system in all modes to ensure proper operation.
The performance of any heat pump system depends heavily upon proper sizing and quality installation. It can be tempting to skip the step of performing heating and cooling load calculations using ACCA Manual J, especially for a system replacement where you know the size of the existing equipment. It is vital that this step be performed for every job, however, to protect the homeowner from paying more than is necessary, to enable a properly performing system, and to protect the contractor from liability.
Quality installation is arguably much more important than the make and model of the selected equipment when it comes to system performance, efficiency, and longevity. Proper refrigerant charge, secure connections, and overall quality work have long-term financial, environmental, and comfort implications.
For ENERGY STAR and DOE Zero Energy Ready Home climate-specific guidance, see the Compliance tab.
Considerations for Cold-Climate Applications
- When selecting equipment, review manufacturer data and examine capacities and efficiencies at low temperatures. See NEEP recommendations for cold-climate heat pumps.
- Install outdoor units well above snow height – stands can be used, as well as wall mounts. Be aware of potential vibration issues if the unit is attached to a wall.
- Do not install outdoor units where water or melting snow or ice will fall on the unit. If located in such places, protect heat pumps with a cover of some sort. For instance, the location should be under the gable end of the roof, as opposed to under an eave end (snow can slide off an eave and land on the unit). See Figures 1 and 2.
- Avoid installing the outdoor unit near a walkway to avoid slippery conditions from water produced by the unit.
- Think about which spaces need heating or cooling in winter and summer. Since hot air rises, it is possible that some homes may be heated sufficiently from the first floor in the winter. In the summer, the hottest part of a house may be the upper floors. The house may be cooled sufficiently from the upper floors. Both strategies require a fairly open connection between floors.
- Indoor fan coils mounted near the ceiling will draw warmer return air from the space. While this is desirable during the cooling season, it is an efficiency liability during the heating season. Ductless fan coils may need to be mounted high so as not to obstruct movement within a home, but for heating performance, lower installations are better.
- In general, heat pumps are most efficient when indoor fan speed is set to “auto.” If fan speed is manually set to one particular speed, capacity and efficiency may be reduced.
The map in Figure 3 shows the climate zones for states that have adopted energy codes equivalent to the International Energy Conservation Code (IECC) 2009, 12, 15, and 18. The map in Figure 4 shows the climate zones for states that have adopted energy codes equivalent to the IECC 2021. Climate zone-specific requirements specified in the IECC are shown in the Compliance Tab of this guide.
The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.
ENERGY STAR Single-Family New Homes, Version 3/3.1 (Rev. 11)
The ENERGY STAR Reference Design Home is the set of efficiency features modeled to determine the ENERGY STAR ERI (energy rating index) Target for each home pursuing certification. Therefore, while the features below are not mandatory, if they are not used then other measures will be needed to achieve the ENERGY STAR ERI Target. In addition, note that the Mandatory Requirements for All Certified Homes, Exhibit 2 (see list below), contain additional requirements such as total duct leakage limits, minimum allowed insulation levels, and minimum allowed fenestration performance. Therefore, EPA recommends that partners review the documents in Exhibit 2 prior to selecting measures.
Please note that the Reference Design Home HVAC efficiencies for Version 3.1 differ from those for Version 3.0. Please see the ENERGY STAR Single-Family New Homes Implementation Timeline for the program version and revision currently applicable in in your state.
Exhibit 2 of the National Program Requirements for ENERGY STAR Certified Homes Version 3/3.1 (Rev. 11) requires that homes complete the following checklists:
National Rater Design Review Checklist (Track B)
1. Partnership Status.
1.2 Rater has verified and documented 8 that HVAC contractor holds credential required to complete National HVAC Commissioning Checklist, unless all equipment to be installed in home to be certified is an exempted type, in which case check “N/A”. 9
Footnote 9) HVAC contractors must be credentialed by an EPA-recognized HVAC Quality Installation Training and Oversight Organization (HQUITO) if a split air conditioner, unitary air conditioner, air-source heat pump, or water-source (i.e., geothermal) heat pump up to 65 kBtuh with a forced-air distribution system (i.e., ducts) or a furnace up to 225 kBtuh with a forced-air distribution system (i.e., ducts) will be installed in the home to be certified. For all other permutations of equipment (e.g., boilers, mini-split / multi-split systems) and distribution systems, a credential is not required. An explanation of this credentialing process and links to H-QUITOs, which maintain lists of credentialed contractors, can be found at energystar.gov/newhomeshvac.
DOE Zero Energy Ready Home (Revision 07)
Exhibit 1 Mandatory Requirements.
Exhibit 1, Item 1) Certified under the ENERGY STAR Qualified Homes Program or the ENERGY STAR Multifamily New Construction Program.
Exhibit 2 DOE Zero Energy Ready Home Target Home.
The U.S. Department of Energy’s Zero Energy Ready Home program allows builders to choose a prescriptive or performance path. The DOE Zero Energy Ready Home prescriptive path requires builders to meet or exceed the minimum HVAC efficiencies listed in Exhibit 2 of the National Program Requirements (Rev 07), as shown below. The DOE Zero Energy Ready Home performance path allows builders to select a custom combination of measures for each home that is equivalent in performance to the minimum HERS (Home Energy Rating System) index of a modeled target home that meets the requirements of Exhibit 2 as well as the mandatory requirements of Zero Energy Ready Home Exhibit 1.
Footnote 21) DOE recommends, but does not require, that cooling systems in hot/humid climates utilize controls for immediate blower shutoff after condenser shutoff, to prevent re-evaporation of moisture off the wet coil.
Footnote 22) Air source heat pumps with electric resistance backup cannot be used in homes qualified in Climate Zones 7 & 8 using the Prescriptive Path.
Washington and California residents – please see the DOE Zero Energy Ready Home website for state-specific requirements.
2009, 2012, 2015, 2018, and 2021 International Energy Conservation Code (IECC)
R403.1 (R403.1.1 in 2015, 2018, and 2021 IECC) Each heating and cooling system should have its own thermostat. If the primary heating system is a forced-air furnace, at least one thermostat must be programmable and capable of controlling the heating and cooling system on a schedule to maintain different temperatures at different times of the day.
R403.6 (R403.7 in 2015, 2018, and 2021 IECC) Heating and cooling equipment shall be sized in accordance with ACCA Manual S based on building loads calculated in accordance with ACCA Manual J or other approved heating and cooling calculation methods.
Retrofit: 2009, 2012, 2015, 2018, and 2021 IECC
Section R101.4.3 (in 2009 and 2012). Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with this code. (See code for additional requirements and exceptions.)
Chapter 5 (in 2015, 2018, 2021). The provisions of this chapter shall control the alteration, repair, addition, and change of occupancy of existing buildings and structures.
2009, 2012, 2015, 2018, and 2021 International Residential Code (IRC)
Comply with all relevant sections of the applicable International Residential Code, including Chapter 14: Heating and Cooling Equipment.
Retrofit: 2009, 2012, 2015, 2018, and 2021 IRC
Section R102.7.1 Additions, alterations, or repairs. Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with the requirements of this code, unless otherwise stated. (See code for additional requirements and exceptions.)
Appendix J regulates the repair, renovation, alteration, and reconstruction of existing buildings and is intended to encourage their continued safe use.
Air Conditioning Contractors of America (ACCA) Standards
ACCA Manual S. Residential Equipment Selection, American National Standards Institute (ANSI)/ACCA 3-Manual S-2014, provides information on how to select and size heating and cooling equipment to meet Manual J loads based on local climate and ambient conditions at the building site. Manual S covers sizing strategies for all types of cooling and heating equipment, as well as comprehensive manufacturers’ performance data on sensible, latent, or heating capacity for various operating conditions.
ACCA Manual D: Residential Duct Systems, ANSI/ACCA 1-Manual D-2016, provides ANSI-recognized duct sizing principles and calculations that apply to all duct materials; the system operating point (supply cfm and external static pressure) and airway sizing for single-speed and multi-speed (ECM) blowers; a method for determining the impact of duct friction and fitting pressure drop on blower performance and air delivery; and equivalent length data.
ACCA Manual J: Residential Load Calculation, ANSI/ACCA 2-Manual J-2016, provides information for calculating heating and cooling loads for equipment sizing for single-family detached homes, small multi-unit structures, condominiums, town houses, and manufactured homes.
ACCA Standard 5: Heating Ventilation Air Conditioning (HVAC) Quality Installation Specification, ANSI/ACCA 5 QI-2010, details nationally recognized criteria for the proper installation of residential and commercial HVAC systems, including forced air furnaces, boilers, air conditioners, and heat pumps. The Standard covers aspects of design, installation, and distribution systems, as well as necessary documentation. The Technician’s Guide for Quality Installation, produced by ACCA, explains the HVAC Quality Installation (QI) Specification and provides detailed procedures for the steps technicians must complete and document to show compliance with the HVAC QI Specification.
ACCA Standard 9: HVAC Quality Installation Verification Protocols, ANSI/ACCA 9 QIVP-2009, specifies the protocols to verify the installation of HVAC systems in accordance with ACCA Standard 5. The protocols provide guidance to contractors, verifiers, and administrators who participate in verification efforts using independent objective and qualified third parties to ensure that an HVAC installation meets the requirements in Standard 5.
- Assess the need for replacing or upgrading the HVAC system. See Pre-Retrofit Assessment of Existing HVAC Systems.
- Review the guide Pre-Retrofit Assessment of Combustion Appliances to ensure safe conditions exist and unsafe conditions won’t be introduced if combustion appliances are replaced or if other energy-efficiency upgrades are made to a home with combustion appliances.
- View the Standard Work Specifications regarding heat pump controls.
The typical lifespan of HVAC equipment is 15 to 20 years. New equipment has much higher efficiencies, safety, control flexibility, and performance capabilities. Existing equipment should be carefully assessed to determine whether investment in repairs, upgrades, or expansion is warranted. See the following BASC guides and resources for information to aid in making this determination. The guides also contain important safety and health information for dealing with older construction and equipment.
- Pre-Retrofit Assessment of Existing HVAC Systems
- Building America Best Practices Series Volume 14 - HVAC: A Guide for Contractors to Share with Homeowners
Ductless mini-split heat pumps are a popular choice for supplementing or replacing heating and cooling equipment in a home that does not already have ducts, for example in a home that currently uses baseboard or wall unit electric heaters or wood stove heating. They have the added advantage of providing cooling in addition to heating. They are sometimes added to a home to become the primary heating and cooling system while an older, less efficient system stays in place to provide back-up heat in cases of very cold weather.
Although installing new HVAC equipment can be costly and labor-intensive, it often reaps large rewards in energy cost savings and comfort. For decision-making guidance including a discussion of the available system types and their advantages, see Pre-Retrofit Assessment of Existing HVAC Systems and Building America Best Practices Series Volume 14 - HVAC: A Guide for Contractors to Share with Homeowners. See the following Solution Center guides for more specific information on other HVAC systems:
- Mechanical Air-Conditioning
- Evaporative Cooling Systems
- Traditional Split Heat Pumps
- Ground-Source Heat Pumps
Full system maintenance is often overlooked by homeowners who don’t understand the strong relationship between general maintenance and performance.
The Air Conditioning Contractors of America Association, Inc. (ACCA) is one of the best sources for guidance on the installation, commissioning, and maintenance of HVAC equipment. Their free Quality Standards can be found on the ACCA website.
Useful documents available for download from the ACCA website include the following:
- ACCA Standard 5: HVAC Quality Installation Specification - minimum design and installation requirements for HVAC applications by professional contractors following industry-recognized quality installation practices.
- ACCA Standard 12: Home Evaluation and Performance Improvement - minimum requirements to evaluate a residence with regard to energy efficiency, water conservation, occupant comfort, and indoor air quality.
- ACCA Standard 9: HVAC Quality Installation Verification Protocols - details the requirements, roles, and obligations of installers and others to ensure that HVAC installations comply with the ANSI/ACCA 5.
- ACCA Standard 4: Maintenance of Residential HVAC Systems - establishes the minimum level of acceptable compliance for HVAC equipment maintenance inspections for residential applications.
- ACCA Standard 6: Restoring the Cleanliness of HVAC Systems - procedures for cleaning HVAC systems.
Ductless mini-split heat pumps are an excellent choice for providing heating and cooling when additional rooms will be added to the home, or when an attic, basement, or garage will be converted to living space. If the home already has an existing mini-split heat pump with multiple indoor heads, the existing system may have sufficient capacity to extend conditioning to the additional space. This should be confirmed by performing an accurate load calculation (ACCA Manual J) for the entire house including the addition. If the current system doesn’t meet the additional needed capacity (and/or for increased efficiency or for zone control) you may decide to add a new, dedicated mini-split heat pump with a separate external compressor/condenser unit.
In some cases, a dedicated mini-split may be desirable for zone control and comfort even where the capacity of the existing HVAC system is sufficient to condition the additional space. Additions that tend to heat-up or cool-down at a much different rate compared to the main house may be good candidates for a dedicated mini-split. Two examples are a sun room addition with lots of glass, or an addition with five exposed sides (three exterior walls, an insulated ceiling, and a floor over unconditioned space) such as a bonus room above a garage.
When selecting a separate unit, perform an accurate load calculation in accordance with ACCA Manual J, select the proper capacity equipment in accordance with ACCA Manual S, and design the duct system in accordance with ACCA Manual D (where applicable).
Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.
New Whole-House Solutions Case Study: Technology Solutions for New Manufactured Homes, Idaho, Oregon, and Washington
Building America Best Practices Series Volume 14: HVAC: A Guide for Contractors to Share with Homeowners
The following authors and organizations contributed to the content in this Guide.
Ductless Mini-Split Heat Pump = High-Efficiency or Ultra-Efficient Ductless Heat Pump
In addition to the savings that come with being an efficient heat pump, ductless heat pumps save energy and money by avoiding the use of ducts or using much more compact duct layouts inside the conditioned space. That’s because ducts are often sources of heat loss where not properly insulated and sealed, especially if installed in unconditioned attics or crawlspaces. The indoor unit is mounted on a wall, where it directly warms or cools a large part of the home. More than one indoor unit can be placed in the home in combination with a single outdoor unit. Additionally, some indoor units can be integrated with simple duct layouts. The outdoor units are smaller than standard heat pumps.