THE SHORT ANSWER
If your cooling equipment is changing, the past electric bill remains useful evidence but is not automatically the best forecast of future consumption. Keep the proposed HVAC change visible instead of subtracting a generic savings percentage from the entire house.
Put the two project dates on one page
Record when the old equipment was operating, when replacement is expected and which bills will include a mixture of both systems. For a Tampa Bay household reviewing solar during a cooling project, a twelve-month total can span very different equipment conditions. Label those periods before anyone uses the total to recommend an array. This does not mean discarding old bills; it means explaining what they represent.
Do not compare efficiency labels casually
DOE notes that the HVAC test procedures and rating nomenclature changed to SEER2 and HSPF2 in 2023. [1] Have the HVAC professional explain a valid comparison between the actual old and new systems. Do not divide two differently based label numbers and announce that the result is a verified household electricity reduction. The equipment rating is one input, not a measurement of every appliance in the home.
Change only the cooling portion of a scenario
Ask for a solar baseline with the measured household total, a separately identified estimate of cooling use and a documented adjustment for the proposed replacement. Leave other loads unchanged unless there is a reason to alter them. If cooling use has not been measured, show more than one clearly labeled assumption rather than presenting an invented precise value. Keep planned EV or pool changes on their own lines.
Use new bills as evidence without overclaiming
After replacement, compare records that account for billing days, household occupancy and relevant weather differences. One mild month cannot establish a permanent savings percentage. Ask the reviewers when there is enough useful data to refine the solar baseline. The decision may be to model a range now and revisit it, rather than commit to an oversized array or postpone every conversation indefinitely.
Let each provider own the right conclusion
Your HVAC professional evaluates the cooling equipment and expected operating changes; the solar designer evaluates the array against the agreed consumption assumptions. Origin’s solar review should preserve that distinction and not imply an HVAC service offering. Bring both project scopes to the conversation so that the same supposed energy reduction is not counted twice in a combined savings presentation.
Before your next conversation
- Mark old and new HVAC operating periods.
- Get a valid equipment-efficiency comparison.
- Adjust cooling use separately from the whole-home total.
Primary sources
- U.S. Department of Energy: Residential Central Air Conditioners
Primary reference checked September 9, 2026. Applies only to the named program or equipment; confirm current terms for your property.
Planning examples and questions are Origin’s editorial guidance, not a property-specific diagnosis, engineering design, tax determination or promise of savings. Manufacturer and utility references do not imply an affiliation with Origin.
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