Massachusetts HVAC & Mass Save Glossary

By MassHVAC Editorial Team Reviewed by MassHVAC Editorial Team Last updated 2026-05-27

Rebates & Mass Save

Basic Heat Pump Rebate: New for 2026: $250/ton, capped at $2,500. Applies to heat-pump-to-heat-pump replacements or conditioning a previously-unconditioned space under 500 sq ft.
Enhanced Heat Pump Rebate: Mass Save's income-qualified tier (households roughly 60–135% SMI): replaces the $8,500 air-source cap with up to $16,000, and the geothermal cap with up to $25,000.
HEAT Loan Mass Save HEAT Loan: 0% APR financing up to $25,000 for qualifying high-efficiency upgrades in Massachusetts, including heat pumps. Effective January 1, 2025 the term is SMI-tiered: 84 months below 135% SMI, 60 months for 135–300% SMI, 36 months above 300% SMI.
Mass Save: The collaborative residential energy efficiency program operated by six Massachusetts utility sponsors — Eversource, National Grid, Unitil, Cape Light Compact, Berkshire Gas, and Liberty Utilities. Mass Save administers heat pump rebates, the HEAT Loan, and Home Energy Assessments on behalf of the participating utilities.
Mass Save sponsor: The specific utility company that administers Mass Save programs for your address. Determined by your electric and gas distribution provider, not by your supplier. Mismatched fuels (e.g. Eversource electric + National Grid gas) are routed through two sponsors.
Partial-Home / Supplemental Heat Pump Rebate: The Mass Save tier (2026: $1,125/ton, $8,500 cap) that applies when the heat pump supplements an existing primary heating system rather than replacing it.
Right-Sized Equipment Bonus: A $500 bonus stacked on partial-home installs where the equipment is sized to 90–120% of the total heating load at the outdoor design temperature, documented via an ACCA Manual J load calculation.
SMI State Median Income: A Massachusetts statewide income reference used by Mass Save to tier the HEAT Loan term length (84/60/36 months for below 135% / 135–300% / over 300% SMI). For a four-person household in 2026, SMI is approximately $121,000.
Turnkey (No-Cost) Heat Pump Program: Mass Save's path for households at or below 60% SMI: program administrators wrap project management, contractor selection, install, and rebate filing into a zero-out-of-pocket package.
Weatherization Bonus: A $500 bonus stacked on partial-home installs when a Mass Save Home Energy Assessment is completed and recommended air sealing or insulation is installed within one year prior to or up to six months after the heat pump.
Whole-Home Heat Pump Rebate: The Mass Save tier (2026: $2,650/ton, capped at $8,500 per home) that applies when the installed heat pump serves as the sole source of heating and cooling for the spaces it conditions. Down from $3,000/ton in 2025.

Federal programs

AMI Area Median Income: A HUD-published county-level (or metro-area-level) income reference used by HEAR for eligibility. The 80% AMI threshold qualifies a household for the federal HEAR rebate.
HEAR Home Electrification and Appliance Rebates: The Inflation Reduction Act-funded federal rebate program (separate from the expired §25C tax credit) that pays Massachusetts households at or below 80% Area Median Income up to $8,000 toward a heat pump. Massachusetts allocation: $72.8 million. Stacks with Mass Save.
HOMES Home Efficiency Rebates: The other IRA-funded rebate program ($73.2M in MA), aimed at whole-home retrofits that combine weatherization with electrification. Delivered through the Mass Save Deep Energy Retrofit pathway.
IRA Inflation Reduction Act: The 2022 federal law that originally extended §25C and §25D through 2032 and appropriated the HEAR and HOMES rebate programs. The IRA-funded rebate programs (HEAR/HOMES) survived OBBBA because they are appropriations, not tax credits.
OBBBA One Big Beautiful Bill Act: Public Law 119-21 (139 Stat. 72), signed July 4, 2025. Terminated multiple Inflation Reduction Act energy provisions including §25C and §25D for property placed in service or expenditures made after December 31, 2025.
Section 25C Energy Efficient Home Improvement Credit: The federal tax credit (up to $2,000 annually for heat pumps) that ended for property placed in service after December 31, 2025 under the One Big Beautiful Bill Act. Not currently available in 2026.
Section 25D Residential Clean Energy Credit: The federal 30% tax credit for ground-source heat pumps and other residential clean energy property. Ended for expenditures made after December 31, 2025 under OBBBA. Pre-2026 installs may carry forward unused credits.

Equipment & installer credentials

Air-Source Heat Pump ASHP: A heat pump that exchanges heat with outdoor air via a condenser-and-evaporator pair. The most common heat pump type in Massachusetts.
Central Air Conditioning central AC: A traditional cooling-only system with a single outdoor condenser and a ducted indoor air handler. Does not qualify for Mass Save heat pump rebates on its own.
Cold-Climate Heat Pump ccASHP: A heat pump designed to maintain rated heating capacity at and below 5°F outdoor temperature. Mass Save requires Cold Climate certification for whole-home rebate eligibility in MA.
Ductless Mini-Split: A heat pump system that uses one or more wall- or ceiling-mounted indoor "heads" connected to an outdoor compressor via small refrigerant lines, with no ductwork. The dominant retrofit choice in pre-1940 Massachusetts housing.
ENERGY STAR Cold Climate: A subcategory of ENERGY STAR heat pump certification for systems that maintain rated heating capacity at low ambient temperatures. Required for Mass Save whole-home rebate qualification in Massachusetts' climate zone 5A/6A.
Ground-Source Heat Pump GSHP / geothermal: A heat pump that exchanges heat with a closed-loop water circuit buried in the ground rather than with outdoor air. Higher efficiency than an ASHP, especially in deep cold, but with substantially higher install cost ($30,000–$60,000 in MA).
Heat Pump: A two-way HVAC system that moves heat between indoor and outdoor air using a vapor-compression refrigerant cycle. In cooling mode it acts like a conventional AC; in heating mode it extracts heat from outdoor air (even cold air) and delivers it indoors. The dominant Mass Save-eligible HVAC technology in 2026.
HPIN Heat Pump Installer Network: The Mass Save-administered list of contractors trained and audited to deliver rebate-eligible heat pump installations. Hiring an installer outside HPIN forfeits the homeowner's Mass Save rebate, even if the equipment itself would have qualified.
HPQPL Heat Pump Qualified Products List: The Mass Save-maintained list of specific heat pump models eligible for the rebate. Equipment must be ENERGY STAR Cold Climate certified and on the current HPQPL to qualify. R-410A units were removed from the HPQPL January 1, 2026.
HSPF / HSPF2: Heating Seasonal Performance Factor — a measure of heat pump heating efficiency. HSPF2 (the post-2023 metric) typical minimums for Mass Save HPQPL listing: 8.1 single-zone, 7.5 multi-zone (cold-climate).
Refrigeration Technician License RT license: A Massachusetts state license issued by the Board of Examiners that authorizes a technician to install or service refrigeration and HVAC equipment. Required for legal HVAC work in MA. Gas connections require a separate gas fitter license.
SEER / SEER2: Seasonal Energy Efficiency Ratio — a measure of cooling efficiency. SEER2 (the post-2023 metric) typical minimums: 15.2 single-zone, 14.3 multi-zone for HPQPL.
VRF Variable Refrigerant Flow: A multi-zone heat pump system common in light-commercial and large-home applications. R-410A VRF systems retain a January 1, 2027 cutoff exception (vs. the general January 1, 2026 cutoff for split systems).

Sizing & load calculation

99% Winter Design Temperature: The ASHRAE-published outdoor dry-bulb temperature that is exceeded 99% of the year at a specific location. Used as the heating-load reference temperature in Manual J. Boston Logan: 12.4°F. Worcester: 6.2°F. New Bedford: 11.9°F.
ACCA Air Conditioning Contractors of America: The industry trade association that publishes Manual J (load calculation), Manual S (equipment selection), and Manual D (duct design). All three are the accepted standards for properly sizing and laying out residential HVAC systems.
Manual J ACCA Manual J: The ACCA-standard residential heating and cooling load calculation. For Mass Save partial-home installs, Manual J is required to qualify for the $500 sizing bonus and to document the 90–120% load match. Reputable installers run Manual J on every Mass Save project regardless.
Ton (HVAC): A unit of heating or cooling capacity equal to 12,000 BTU/hour. Massachusetts single-family homes typically need 2–5 tons of heat-pump capacity, sized via Manual J — not square-foot rules of thumb.

Refrigerants

GWP Global Warming Potential: The relative climate impact of a refrigerant compared to CO₂ (which has GWP = 1) over a 100-year window. EPA rules effective January 1, 2026 prohibit installation of new residential heat pumps using refrigerants with GWP greater than 700.
R-32: A lower-GWP (~675) refrigerant approved for residential heat pumps post-R-410A. Mildly flammable (A2L classification), requiring updated installation training.
R-410A: A hydrofluorocarbon refrigerant blend with global warming potential (GWP) of ~2,088. Phased out from new residential and light-commercial heat pump installs effective January 1, 2026 because GWP exceeds the EPA cap of 700. VRF systems retain a Jan 1, 2027 exception; factory-charged self-contained products through Jan 1, 2028.
R-454B: Another lower-GWP (~466) refrigerant blend approved for residential heat pumps post-R-410A. Also A2L-classified.

Utilities & sponsors

MLP Municipal Light Plant: A city- or town-owned electric utility (e.g. Belmont, Braintree, Reading, Wakefield). MLP customers do not pay into the Energy Efficiency Charge that funds Mass Save and therefore are not eligible for Mass Save rebates or the HEAT Loan. Most MLPs run their own rebate programs and the parallel MLP Zero-Interest Energy Efficiency Loan applies statewide.

Process

Home Energy Assessment: A free, ~60–90 minute on-site evaluation conducted by a Mass Save-contracted auditor. Required to access the HEAT Loan, HEAR rebates, and Mass Save income-eligible programs. Typical lead time: 4–6 weeks.

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