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Traditional Split Heat Pumps

Scope

Choose the highest performing heating and cooling equipment that project funding will allow, to meet the design load of the project.

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. 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 manufacturers’ instructions and relevant standards including ACCA Standard 5: HVAC Quality Installation Specification and the ACCA’s Technician's Guide for Quality Installations and ACCA Standard 9: HVAC Quality Installation Verification Protocols.

Properly size the equipment for the design heating or cooling load of the home (whichever is larger), following the sizing guidelines in ACCA Manual S: Residential Equipment Selection. Calculate the heating and cooling load using the ACCA Manual J Residential Load Calculation. 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 SEER and EER cooling efficiencies at factory conditions of 90°F outdoor, 80°F indoor, and 67°F wet bulb.

The OEM-listed total cooling capacity at design conditions should be between 95% and 115% of the design total heat gain (or 95% to 125% for heat pumps in IECC climate zones 4-8)  or the next nominal size. The next largest nominal piece of equipment available may be used to satisfy the latent and sensible cooling requirements. Single-speed systems generally have OEM nominal size increments of one-half ton. Multi-speed or multi-stage equipment may have OEM nominal size increments of one ton. Therefore, the use of these advanced system types can provide extra flexibility to meet the equipment sizing requirements.

If the whole-house ventilation system uses the heat pump air handler, then the fan motor should be a variable speed electronically commutated motor (ECM) or an integral control motor (ICM) that includes a controller (e.g., a smart cycler) that reduces the ventilation run time by accounting for hours when the HVAC system is already operating the fan for heating or cooling the home.

Design an efficient air distribution system with a compact layout in accordance with ACCA Manual D: Residential Duct Systems. Install ducts properly for maximum airflow and efficiency. Consider zoning for low-load homes (over 1,000 sq ft per ton of cooling) with thermostat-controlled dampers. 

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) 2012 climate zone map on the Climate tab.

DOE Zero Energy Ready Home Notes

The U.S. Department of Energy’s Zero Energy Ready Home program allows builders to choose a prescriptive or performance path. The prescriptive path requires builders to meet or exceed the minimum HVAC efficiencies listed in Exhibit 2 of the DOE Zero Energy Ready Home National Program Requirements. 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 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. See the Compliance tab for specific program details.

ENERGY STAR Certified Homes Notes

The ENERGY STAR Certified Homes program allows builders to choose a prescriptive or performance path. The ENERGY STAR prescriptive path requires builders to meet the minimum HVAC efficiencies listed in Exhibit 1 of the National Program Requirements for ENERGY STAR Certified Homes. The ENERGY STAR performance path allows builders to select a custom combination of measures for each home that is equivalent in performance to the minimum HERS index of a modeled reference home that meets the requirements of ENERGY STAR Exhibit 1 as well as the mandatory requirements of Exhibit 2. See the Compliance tab for specific program details.

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.

Description

Heat pumps use the same refrigeration cycle technology as your home’s refrigerator or air conditioner, pulling heat from one environment and dumping it into another. Unlike air conditioners made for cooling only, heat pumps are equipped with a reversing valve, which allows them to reverse the cycle to pull heat from the outdoor air and deliver it indoors in the winter time. Most heat pumps installed in U.S. homes are central air-source heat pumps that draw heat from or shed heat to the outside air. A much smaller percentage of homes are equipped with ground source or water source heat pumps.

Most of these air-source heat pumps are split systems with an indoor unit and an outdoor unit that are connected by refrigerant lines (Figure 1). The indoor unit includes an evaporator coil and a metering device that are located in the air handler unit, which also contains a blower fan that blows the conditioned air into the supply ducts for distribution throughout the house and receives stale house air from the return ducts. The outside unit contains the condenser and the compressor. For more on the refrigerant cycle, see Compression Cooling. Heat pumps (and air conditioners) are also available as packaged units, where the compressor, condenser, evaporator, and expansion device are all packed into one unit that is located outside, typically mounted on the wall or on the roof (Figure 2). The conditioned air is vented inside, either directly into a room or into a duct system for distribution throughout the home. A window air conditioner is a good example of a package unit. Many small commercial buildings are cooled with roof-mounted packaged air conditioning units.

Split-system air source heat pump
Figure 1. Split-system air-source heat pumps have an outside unit with a compressor and condenser and an inside unit with an evaporator, refrigerant metering device, reversing valve, and blower fan, to push air into the ducts. 

Packaged unit heat pump
Figure 2. This packaged unit heat pump has all components located in one box outside the home.

Split unit heat pump
Figure 3. This split unit heat pump has the compressor and condenser outside and the evaporator, refrigerant metering device, and distribution fan inside the home.

 Central heat pumps distribute the heated or cooled air through ducts, just like a central forced-air furnace. Another form of heat pump is the ductless mini-split heat pump. These split-systems feature a small ground- or wall-mounted outdoor unit connected via refrigerant lines to one or more indoor wall- or ceiling-mounted units that heat and cool the space they are in without the use of ducts.

Because the heating efficiency of standard, central air-source heat pumps drops when outside temperatures drop below about 35°F, a backup heat source is often needed in cold climates. Air-source heat pumps can be all-electric or dual-fuel systems. All-electric air-source heat pumps come equipped with electric resistance strip heaters for supplementary heat if needed. Dual-fuel systems combine the air-source heat pump with another source of supplementary heat, such as a gas furnace.

When compared to an electric furnace or baseboard heaters, a heat pump can trim the amount of electricity used for heating by 30% or more. The efficiency of today's air-source heat pumps is one to two times greater than those available 30 years ago due to technical advances such as thermostatic expansion valves, variable-speed blowers, improved coil design, two-speed compressors (instead of single-speed compressors), and improved motor designs (DOE 2013). Recently available central heat pump models with variable-speed compressor designs that better match refrigerant flow to load can save even more and are more effective at lower outside temperatures. Ductless mini-split heat pump models have been available for several years that use variable-refrigerant-flow technology and can heat at 100% capacity at outdoor temperatures as low as 5°F. For more on ductless heat pumps, see the guide Mini-Split Heat Pumps.

Current federal law requires that air-source heat pumps have a minimum heating efficiency or Heating Season Performance Factor (HSPF) of 7.7 and a minimum cooling efficiency or Seasonal Energy Efficiency Ratio (SEER) of 13. Higher efficiency central air-source heat pump models are available with ratings of up to 13 HSPF and up to about SEER 25 (See ENERGY STAR’s Most Efficient 2014 – Central Air Conditioners and Air Source Heat Pumps). For more on efficiency measurements, see Compression Cooling.

Ducts may need to be larger for a heat pump than for a gas or oil furnace because furnaces generally deliver air to the living space at between 130°F and 140°F. Heat pumps provide air at about 80°F to 115°F so more air needs to be delivered to provide the same amount of warmth. Your HVAC contractor should confirm that the supply air registers achieve a “throw” appropriate for a heat pump. Choosing the right register design can be important for minimizing comfort complaints because heat pumps blow more air at cooler temperatures than gas- or oil-fired furnaces. Some researchers suggest central-air-source heat pumps may need to be slightly oversized, to enable the system to provide enough warmth without turning on the backup heat.

Care should be taken when installing the heat pump system to seal the copper tubing refrigerant lines to keep moisture out of them during construction and the lines should be cleared with a vacuum pump to remove pockets of air before charging the lines with refrigerant. Any water or water vapor in the lines will mix with the oil used for lubricant in the refrigeration system creating an acidic sludge that eats away at compressor windings and clogs valve openings. Care should also be taken to follow the manufacturer’s specifications regarding the correct method for charging the refrigerant with the model to be installed. Too much or too little refrigerant can affect performance and efficiency.

How to Select and Install Central Air Source Heat Pumps

  1. Choose the highest performing heat pump project costs will allow, to meet the design heating or cooling load of the project. If you are participating in an energy-efficiency program, select equipment that complies with the requirements for your climate zone, as described in the Compliance tab.
  2. 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 (OEM) indicating an acceptable combination.
  3. Properly size the heat pump for the design heating or cooling load of the home, whichever is greater. Use ACCA Manual J to calculate your load and use ACCA Manual S to correctly size your system. This is especially important if you have done significant air sealing and insulating, which will reduce your heating and cooling load. 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.
  4. Design an efficient air distribution system with a compact layout in accordance with ACCA Manual D. Install ducts properly for maximum airflow and efficiency in accordance with ACCA Manual D, and ACCA Standards 5 and 9. See also the Building America Solution Center guides on duct installation, insulation, and air sealing.
  5. During construction keep the copper refrigerant tubing charged with dry nitrogen and sealed with solder to keep moisture out of the lines.
  6. After connecting the indoor unit and the outdoor unit, vacuum the lines to 500 microns to remove air pockets.
  7. 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.
  8. Make sure the condensate line and drain pans are correctly installed.
  9. Test air flow and duct leakage.

Ensuring Success

Choose the highest efficiency SEER and HSPF rated product possible.

Verify that the air handler is correctly matched to the outdoor unit. Matched systems can be verified at the AHRI website, listed under "Heat Pumps and Heat Pump Coils."

Install in accordance with the manufacturers’ instructions and relevant standards including ACCA Standard 5: HVAC Quality Installation Specification and the ACCA’s Technician's Guide for Quality Installations and ACCA Standard 9: HVAC Quality Installation Verification Protocols. These standards address quality installation and commissioning requirements for vapor compression cooling systems, heat pumps, combustion furnaces, and boilers.

Install the air handler and ducts within the home’s thermal envelope.

Follow the manufacturer’s recommendations for refrigerant charging.

Set the time-delay relay on the unit to 30 seconds or less in humid climates to prevent moisture on the evaporator coil from evaporating back into the air stream and contributing to indoor humidity. Set the fan on the central air conditioning systems to “Auto” rather than “On” for the most efficient operation. Set the compressor to start before the blower. Make sure the drain pans are correctly installed.

Climate

For ENERGY STAR and DOE Zero Energy Ready Home climate-specific guidance, see the Compliance tab.

In mild or cold climates, consider non-compression cooling options such as trees, awnings, pergolas, and porches to shade windows and walls; ceiling fans; and timer-controlled night-time ventilation cooling (Gilbride et al. 2011).

In humid and mild or cold climates, consider adding a dehumidifier for indoor humidity control in the shoulder seasons and in locations with short summers as an alternative to compression cooling.

In humid climates, set the time-delay relay on the unit to 30 seconds or less to prevent moisture on the evaporator coil from evaporating back into the air stream and contributing to indoor humidity.

To determine your climate zone, see the International Energy Conservation Code (IECC) climate zone map.

IECC climate zones
IECC Climate Zone Map

Training

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Compliance

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.

2009 IECC

403.1 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.

403.2 Ducts - Insulate supply ducts in attics to at least R-8 and all other ducts to at least R-6. Duct tightness shall be verified as described in 403.2.2 Sealing.

403.6 Heating and cooling equipment sizing shall be in accordance with Section M1401.3 of the 2009 International Residential Code.

2012 IECC

403.1 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.

403.2 Ducts - Insulate supply ducts in attics to at least R-8 and all other ducts to at least R-6.
Duct tightness shall be verified as described in 403.2.2 Sealing.

The air handler shall have a manufacturer’s designation showing air leakage is no more than 2% of the design air flow rate when tested in accordance with ASHRAE 193.

403.6 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.

2015 and 2018 IECC

403.1 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.

Section 403.3.1 Insulation (Prescriptive).  Supply and return ducts  in attics insulated to at least R-8 if 3 inches in diameter or more or R-6 if less than 3 inches.  All other ducts insulated to at least R-6 if 3 inches in diameter or more and R-4.2 if less than 3 inches.

The air handler shall have a manufacturer’s designation showing air leakage is no more than 2% of the design air flow rate when tested in accordance with ASHRAE 193.

403.7 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, and 2018 IECC

Section R101.4.3 (Section R501.1.1 in 2015 and 2018 IECC). 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.)

2009, 2012, 2015, and 2018 IRC

Comply with all relevant sections of the applicable International Residential Code, including Chapter 14: Heating and Cooling Equipment.

Retrofit: 2009, 2012, 2015, and 2018 IRC

Section N1101.3 (Section N1107.1.1 in 2015 and 2018 IRC). 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.)

Appendix J regulates the repair, renovation, alteration, and reconstruction of existing buildings and is intended to encourage their continued safe use.

ACCA Standards

ACCA Manual S. Residential Equipment Selection, ANSI/ACCA 3-Manual S-2004, 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-2011, 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-2011, 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: 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.

U.S. Department of Energy Zero Energy Ready 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, 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 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.

Exhibit 2: Zero Energy Ready Home Target Home

The DOE Zero Energy Ready Home prescriptive path requires builders to meet or exceed the minimum HVAC efficiencies listed in Exhibit 2. 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 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.

Zero Energy Ready Home Notes:

(7) State energy code specifications that exceed the DOE Zero Energy Ready Home National Program Requirements always take precedence and shall be used instead of DOE Zero Energy Ready Home specifications to determine DOE Zero Energy Ready Home compliance.

(20)  Use the 2012 IECC Climate zone map.

(22) 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.

(23) 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.

ENERGY STAR Version 3 (Rev 07)

The ENERGY STAR Certified Homes program allows builders to choose a prescriptive or performance path.

The ENERGY STAR prescriptive path requires builders to meet the minimum HVAC efficiencies listed in Exhibit 1. The ENERGY STAR performance path allows builders to select a custom combination of measures for each home that is equivalent in performance to the minimum HERS index of a modeled reference home that meets the requirements of Exhibit 1 as well as the mandatory requirements of ENERGY STAR Exhibit 2.

Exhibit 1: ENERGY STAR Reference Design

Follow the criteria in the ENERGY STAR HVAC System Quality Installation Contractor and Rater Checklists.

ENERGY STAR Footnotes:

From the ENERGY STAR Certified Homes National Program Requirements:

17. For Prescriptive Path: The required efficiency for air source heat pumps in Climate Zones 4, 5, & 6 exceeds the ENERGY STAR minimum of 8.2 HSPF. Air source heat pumps with electric resistance backup heating cannot be used in homes certified in Climate Zones 7 & 8 using the Prescriptive Path.

23. For homes with heat pumps that contain an electric resistance heating element used to supplement the capacity of the heat pump, the thermostat shall have ‘Adaptive Recovery’ technology to prevent excessive use of the heating element.

From the ENERGY STAR HVAC System Quality Installation Contractor Checklist:

(1) This Checklist applies to ventilation systems, split air conditioners, unitary air conditioners, air-source heat pumps, and water-source (i.e., geothermal) heat pumps up to 65,000 Btu / h with forced-air distribution systems (i.e., ducts) and to furnaces up to 225,000 Btu / h with forced-air distribution systems (i.e., ducts). All other permutations of equipment (e.g., boilers, mini-split / multi-split systems) and distribution systems are exempt. If the ventilation system is the only applicable system installed in the home, then only Section 1 shall be completed.
One Checklist shall be completed for each system and provided to the Rater.

(8) Heating and cooling loads shall be calculated, equipment shall be selected, and duct systems shall be sized according to the latest editions of ACCA Manuals J, S, & D, respectively, 2009 ASHRAE Handbook of Fundamentals, or other methodology approved by the Authority Having Jurisdiction. The HVAC system design shall be completed for the specific configuration (e.g., plan, elevation, option, and orientation) of the home to be built except as permitted herein.
For each house plan with multiple configurations (e.g., orientations, elevations, options), the loads shall be calculated for each potential configuration. If the loads across all configurations vary by <= 25%, then the largest load shall be permitted to be used for equipment selection for all configurations, subject to the over-sizing limits of ACCA Manual S. Otherwise, the contractor shall group the load for each configuration into a set with <= 25% variation and equipment selection shall be completed for each set of loads.

For each house plan with multiple configurations, the room-level design airflows shall be calculated for each potential configuration. If the design airflows for each room vary across all configurations by <= 25% or 25 CFM, then the average room-level design airflow shall be permitted to be used when designing the duct system. Otherwise, the contractor shall group the room-level design airflow for each configuration into a set with <= 25% or 25 CFM variation and the duct design shall be completed for the average airflow of that set.

(13) Design airflow is the design value(s) for the blower in CFM, as determined by using the manufacturer’s expanded performance data to select equipment, per ACCA Manual S procedures.

(14) Design duct static pressure shall account for the installation of a MERV 6 or higher filter.

(15) The load calculation for the home shall be provided, documenting all design elements and all resulting loads, including but not limited to the values listed in Items 2.1 through 2.17.

(16) All evaporators and condensing units shall be properly matched as demonstrated by an attached AHRI certificate. If an AHRI certificate is not available, a copy of OEM-provided catalog data indicating acceptable combination selection and performance data shall be attached.

(17) If the whole-house ventilation system utilizes the HVAC air handler, then the fan speed type shall be ECM / ICM and variable speed, or include a controller (e.g., smart cycler) that reduces the ventilation run time by accounting for hours when HVAC system is heating or cooling the home.

(18) Listed system capacity at design conditions is to be obtained from the OEM expanded performance data.

(19) For cooling systems, the next largest nominal piece of equipment may be used that is available to satisfy the latent and sensible requirements. Single-speed systems generally have OEM nominal size increments of ½ ton. Multi-speed or multi-stage equipment may have OEM nominal size increments of one ton. Therefore, the use of these advanced system types can provide extra flexibility to meet the equipment sizing requirements.

(21) For warm air heating systems, the output capacity must be between 100% and 140% of calculated system load unless a larger size is dictated by the cooling equipment selection.

(22) Either factory-installed or field-installed TXV’s may be used. For field-installed TXV’s, ensure that sensing bulbs are insulated and tightly clamped to the vapor line with good linear thermal contact at the recommended orientation, usually 4 or 8 o’clock.

(23) Examples of return or supply duct static pressure measurement locations are: plenum, cabinet, trunk duct, as well as front, back, left or right side. Test hole locations shall be well marked and accessible.

(24) Ducts shall not include coiled or looped ductwork except to the extent needed for acoustical control. Balancing dampers or proper duct sizing shall be used instead of loops to limit flow to diffusers. When balancing dampers are used, they shall be located at the trunk to limit noise unless the trunk will not be accessible when the balancing process is conducted. In such cases, Opposable Blade Dampers (OBD) or dampers located in the duct boot are permitted.

(25) Condensate pan shall be made of corrosion-resistant materials, to include galvanized steel and plastic. Drain pan shall drain condensate to a conspicuous point of disposal to alert occupants in the event of a stoppage of the primary drainage system; and shall be equipped with a backflow prevention valve when drained to a shared drainage system, such as a storm water management system.

Many states have adopted state- or region-specific ENERGY STAR Certified Homes criteria - Please see the ENERGY STAR Certified Homes website for regional specifications.

This Retrofit tab provides information that helps installers apply this “new home” guide to improvement projects for existing homes. This tab is organized with headings that mirror the new home tabs, such as “Scope,” “Description,” “Success,” etc. If there is no retrofit-specific information for a section, that heading is not included.

SCOPE

Assess the need for replacing or upgrading the HVAC system. See 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 upgraded or replaced or if other energy-efficiency upgrades are made to a home with combustion appliances. 

For more information, see the U.S. Department of Energy’s Standard Work Specifications regarding heat pump controls.

DESCRIPTION

Assessment

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.

Replacement

If the existing HVAC system is a heat pump, current models likely offer much higher efficiencies and can perform at lower outdoor temperatures than those of 15 or 20 years ago. Although replacement of HVAC equipment can be costly and labor-intensive, it often reaps large rewards in energy cost savings and comfort. Use existing utility bills, the estimated replacement equipment cost, the nameplate efficiencies of potential new equipment, and the energy savings estimates provided in Table 1 below to roughly determine expected energy cost savings resulting from replacement of existing HVAC equipment with equipment having higher rated efficiencies.

Annual Estimated Savings for Every $100 of Cooling Costs.
Table 1. Annual Estimated Savings for Every $100 of Cooling Costs. (Source: www.energysavers.gov)

If a decision is made to replace the equipment, it can be replaced in-kind, or with a different type of system. Modern, ducted heat pumps are available in a variety of capacities and efficiencies and can operate at wide temperature ranges, making them a viable alternative to fuel-fired furnaces in all but the coldest climate zones. They have the added advantage of a reversing valve, which allows them to provide either heating or cooling. When comparing heat pumps and furnaces with A/C, perform a full Manual J load calculation to compare annual operating costs, since there is no reliable way to equate AFUE with HSPF.

For decision-making guidance including a discussion of the available system types and their advantages, see 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:

Repair/Upgrade

Full system maintenance is often overlooked by homeowners who don’t understand the strong relationship between general maintenance and performance. Proper commissioning or recommissioning by a certified technician is especially important with compression cooling equipment.

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:

Additions

If additional rooms will be added to the home, or if an attic, basement, or garage will be converted to living space and the home has an existing heat pump with central forced-air air handler, 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 HVAC system to serve the new space independently or you may choose to replace the existing system with a new more efficient system capable of serving the whole house.

When installing new ducts for the addition, consider the following:

  • New ducts should be properly sized in accordance with ACCA Manual D.
  • If using the existing heat pump, simply extending the nearest existing supply branch ducts into an addition is unlikely to deliver sufficient air flow to the addition because that takeoff was not designed for the new (combined) flow requirement. This will result in poor comfort for all spaces dependent on the modified branch, both existing and new.
  • Ideally, install a separate, dedicated supply air trunk duct to serve the addition. This trunk should be run back as close to the furnace/air handling unit as practical. This will ensure that air flow to the addition is removed proportionally from the total system air flow and therefore will not affect the air flow balance in the existing house. Install manual balancing dampers in the supply trunks serving the addition and existing house to allow fine-tuning of the system.
  • If there are interior doors separating the addition - or portions of the addition - from the main house, install transfer grilles, jump ducts, or ducted returns as required to ensure a return air path to the central air handler unit

COMPLIANCE 

See Compliance tab. 

More Info.

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.

Case Studies

  1. Author(s): PNNL
    Organization(s): PNNL
    Publication Date: February, 2013

    Case study describing a new construction project in the mixed-humid climate zone.

  2. Author(s): PNNL
    Organization(s): PNNL
    Publication Date: November, 2013

    Case study about two new construction projects in Florida built to be net zero energy homes.

References and Resources*

  1. Author(s): International Code Council
    Organization(s): ICC
    Publication Date: January, 2009

    Code containing 2009 ICC language for mechanical draft systems.

  2. Author(s): Air Conditioning Contractors of America
    Organization(s): Air Conditioning Contractors of America
    Publication Date: December, 2013
    Standard outlining industry procedure for sizing residential duct systems.
  3. Author(s): Air Conditioning Contractors of America
    Organization(s): Air Conditioning Contractors of America
    Publication Date: January, 2011

    Standard covering equipment sizing loads for single-family-detached homes, small multi-unit structures, condo­miniums, town houses and manufactured homes.

  4. Author(s): Air Conditioning Contractors of America
    Organization(s): Air Conditioning Contractors of America
    Publication Date: April, 2013

    Standard covering sizing strategies for all types of cooling and heating equipment, as well as how to use comprehensive manufacturer’s performance data on sensible, latent, or heating capacity for various operating conditions. 

  5. Author(s): Air Conditioning Contractors of America
    Organization(s): Air Conditioning Contractors of America
    Publication Date: July, 2014

    This Standard establishes the minimum requirements to evaluate a residence with regards to energy efficiency, water conservation, occupant comfort, and indoor air quality.

  6. Author(s): Air Conditioning Contractors of America
    Organization(s): Air Conditioning Contractors of America
    Publication Date: January, 2015

    Standard providing a universally accepted definition for quality installation for residential and commercial heating, ventilating, and air conditioning applications.

  7. Publication Date: January, 2016

    Document detailing the requirements, roles, and obligations for participants in an organized effort, ensuring that HVAC installations comply with the ANSI/ACCA 5 QI – 2010 (HVAC Quality Installation Specification) QI Standard.

  8. Author(s): Natural Resources Canada
    Organization(s): Natural Resources Canada
    Publication Date: April, 2014
    Web resource with information for consumers about air source heat pumps.
  9. Author(s): Baechler, Gilbride, Hefty, Cole, Adams, Butner, Oritz, Love
    Organization(s): Pacific Northwest National Laboratory, Oak Ridge National Laboratory
    Publication Date: September, 2011

    Report describing measures that builders in mixed-humid climates can use to build homes that have whole-house energy savings of 40% over the Building America benchmark with no added overall costs for consumers.

  10. Author(s): Gilbride, Baechler, Hefty, Hand, Love
    Organization(s): Pacific Northwest National Laboratory, Oak Ridge National Laboratory
    Publication Date: August, 2011

    Report providing information about energy-efficient heating, ventilation, and cooling (HVAC) equipment options to help homeowners cut their energy use, reduce their carbon footprint, and increase their homes comfort, health, and safety.

  11. Author(s): AHRI
    Organization(s): AHRI
    Publication Date: January, 2012
    Online database with efficiency information about residential HVAC systems and commercial refrigeration equipment.
  12. Author(s): EIA
    Organization(s): EIA
    Publication Date: January, 2009
    Federal statistics about national energy consumption in residential homes.
  13. Author(s): Department of Energy
    Organization(s): DOE
    Publication Date: May, 2013

    Website with consumer information about residential heat pump systems.

  14. Author(s): RESNET
    Organization(s): RESNET
    Publication Date: January, 2013

    RESNET standards aimed to ensure that accurate and consistent home energy ratings are performed by accredited home energy rating providers through their raters nationwide.

  15. Author(s): Department of Energy
    Organization(s): DOE
    Publication Date: June, 2014

    Website with information from DOE about rules and standards for residential air conditioners and heat pumps.

  16. Author(s): Burdick
    Organization(s): IBACOS, National Renewable Energy Laboratory
    Publication Date: February, 2012

    Report describing the equipment selection of a split system air conditioner and furnace for an example house in Chicago, Illinois, as well as a heat pump system for an example house in Orlando, Florida.

  17. Author(s): Air Conditioning Contractors of America
    Organization(s): ACCA
    Publication Date: January, 2010

    The Technician's Guide equips practitioners with the knowledge to properly implement all of the measurement procedures required in the HVAC QI Specification.

Contributors to this Guide

The following authors and organizations contributed to the content in this Guide.

Last Updated: 08/01/2017