Heating and cooling # What is a VFD? VFD stands for variable frequency drive. A VFD varies the speed of a motor by changing the frequency of the power supplied to it, so a fan or pump can run at part load instead of switching fully on and off. ## What does the acronym stand for? **VFD** — variable frequency drive. ## Is it something you have at home? **Commercial equipment.** This term describes commercial building equipment. It turns up constantly in HVAC search results because much of the industry’s technical writing is aimed at that market rather than at houses. If you met it on a residential quote, ask what is meant before going further. ## Why it matters to you The saving is large because fan power falls much faster than fan speed. In homes the same principle appears under a different name: a variable-speed blower or an inverter-driven compressor is doing this job, and that is where the comfort difference in premium residential equipment comes from. ## Which efficiency numbers can you actually compare? If you are comparing efficiency figures, check which generation they belong to first. On January 1, 2023 DOE changed the test procedure and renamed three metrics: SEER became **SEER2**, EER became **EER2**, and HSPF became **HSPF2**. The current procedure measures at a higher external static pressure, much closer to what equipment meets once installed in a real house on real ductwork. DOE is explicit about the consequence: "Although SEER2, HSPF2, and EER2 ratings are similar to ratings using the original metrics, they are not directly comparable. Compliance with the new standards for each model must be determined based on its measured SEER2, HSPF2, or EER2." In practice: a SEER figure from a 2019 article cannot tell you whether a quote reading SEER2 is good, bad or identical. That is why we publish no conversion factor. We do not publish a SEER-to-SEER2 conversion factor. DOE states that ratings on the new metrics are "not directly comparable" to ratings on the original metrics, and that compliance must be determined from the measured SEER2, EER2 or HSPF2 value. Approximate multipliers circulate widely, but they vary by equipment type and configuration, and using one to compare an old article's number against a number on today's quote is how homeowners end up believing they were offered less efficiency than they were. Compare like with like: ask for the SEER2 figure, and check it against the AHRI certificate. The nationwide minimum for a split-system air conditioner is 13.4 SEER2, and for a split-system heat pump 14.3 SEER2 with 7.5 HSPF2. [What each metric measures](https://hvacbuddy.shop/efficiency/) · [minimums by region and state](https://hvacbuddy.shop/efficiency/standards/). ## What should you know about refrigerant? Refrigerant circulates in a sealed loop. It is not consumed the way fuel or oil is, so a system that is low on charge **has a leak**. Adding refrigerant without finding and repairing that leak treats the symptom, vents the new charge over the following weeks, and costs you the same money again next season. It is also regulated. Only Section 608 certified technicians may purchase refrigerants intended for use with stationary refrigeration and air-conditioning equipment. The restriction covers ozone-depleting substances and non-ozone-depleting substitutes — including HFCs — in cylinders, cans or drums. Wholesalers must record the purchaser's name, the date of sale and the quantity. There is one exception that confuses people: small cans of refrigerant for *vehicle* air conditioning are still sold without certification. That exception is for cars and does not extend to the equipment in your house. For new equipment, the 700 GWP limit in force since January 1, 2025 is why current systems ship with R-454B (GWP 465) or R-32 (GWP 675) rather than R-410A (GWP 2088). R-410A inventory built before 2025 can still be legally installed — EPA removed the installation deadline on May 21, 2026. [The full timeline](https://hvacbuddy.shop/refrigerants/). ## How is the right equipment size decided? Nearly every persistent comfort problem traces back to equipment size, and size is decided before the first box arrives. The standard is the ACCA **Manual J** load calculation (ANSI/ACCA 2 Manual J - 2016), which totals the heat gain and loss of your specific house: orientation, window area and type, insulation levels, air infiltration, internal gains, and your local design temperature. What a Manual J is *not*: square feet per ton, and not the old unit's tonnage. The first ignores everything that makes one house different from another. The second assumes whoever sized the old equipment got it right, and propagates their error for another fifteen years. Oversized equipment reaches the setpoint and shuts off before it has dehumidified, so the house ends up cold and clammy at the same time. Every start is also the hardest moment in a compressor's life, so wear accelerates. And you pay for the surplus capacity twice — once to buy it and again to run it. Ask for the completed Manual J in writing, not the claim that one was done. [What it contains and how to read it](https://hvacbuddy.shop/sizing/manual-j/). Sources (1) - ASHRAE — [ASHRAE Terminology](https://terminology.ashrae.org/) (accessed 2026-08-20) By [HVACBuddy Editorial Team](https://hvacbuddy.shop/authors/editorial-team/). Last reviewed: 2026-08-20. HVACBuddy publishes independent information. We do not install or service equipment, we do not dispatch contractors, and we do not sell leads. Nothing here is engineering, tax, or legal advice.