HVAC Ratings Glossary: SEER2, HSPF2, EER2, AFUE, Tonnage and MERV
Every number on a proposal or data plate, explained in one place.
By Piggies Air Conditioning HVAC Team · Updated · 6 min read · Codes & Ratings
The short answer
SEER2 and EER2 measure cooling efficiency, HSPF2 measures heat pump heating efficiency, and AFUE measures furnace efficiency. Tonnage is cooling capacity (one ton is 12,000 BTU per hour), and MERV rates how fine a filter is. Higher is more efficient or finer in every case, but the right value depends on your house, not the biggest number on the sheet.
Efficiency ratings
- SEER2 (Seasonal Energy Efficiency Ratio 2): cooling output over a season divided by electricity used, under the 2023 federal test procedure. The "2" versions replaced the older SEER, EER and HSPF ratings and are tested with more realistic duct static pressure, so a SEER2 number is slightly lower than the old SEER for the same equipment.
- EER2: efficiency at one fixed, hot test condition. More useful than SEER2 for a San Gabriel Valley afternoon because it reflects performance when it is hot outside.
- HSPF2 (Heating Seasonal Performance Factor 2): the heating-season equivalent of SEER2 for heat pumps.
- AFUE (Annual Fuel Utilization Efficiency): the share of the gas a furnace turns into heat for the house. A 95 AFUE furnace sends about 5 percent of the fuel's energy up the flue.
- COP (Coefficient of Performance): heat delivered divided by electricity used at a single condition. A COP of 3 means three units of heat for one unit of electricity.
Capacity and sizing
- BTU (British thermal unit): the amount of heat that raises one pound of water by one degree Fahrenheit. Equipment is rated in BTU per hour.
- Ton: 12,000 BTU per hour of cooling. A 3-ton system removes 36,000 BTU per hour at rated conditions.
- Manual J: the industry load calculation that determines how many BTU a specific house needs. Manual S selects equipment to match it; Manual D designs the ducts.
- CFM (cubic feet per minute): airflow. A common planning figure is roughly 400 CFM per ton of cooling, adjusted for climate and equipment.
Air quality and airflow
- MERV (Minimum Efficiency Reporting Value): a 1 to 16 scale for how well a filter captures particles. Higher captures finer particles but also restricts airflow more, which is why a thicker media filter is usually the better way to go up in MERV.
- Static pressure: resistance to airflow in the duct system, measured in inches of water column. Too high means the blower is straining.
- Delta T: the temperature difference between return and supply air. Technicians use it as a quick health check.
Paperwork and compliance terms
- Title 24: California's building energy code.
- HERS: third-party field verification of certain Title 24 measures.
- AHRI certificate: confirms a specific indoor and outdoor unit combination and its rated efficiency. Rebate programs usually ask for it.
- SCAQMD: the South Coast Air Quality Management District, which sets emissions rules for gas furnaces and water heaters in our region.
What to remember
- 1 SEER2, EER2 and HSPF2 are the current federal ratings; older SEER numbers are not directly comparable.
- 2 Capacity comes from a Manual J calculation, not from the old unit's size.
- 3 Raise MERV with a thicker filter, not a denser one-inch filter.
This guide is general information for homeowners in Baldwin Park and surrounding communities. Codes, rates and incentive programs change; confirm current terms with the agency or program before relying on a date or amount. For your specific system, book a visit or call us.
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