How Weather Drives Ohio Business Electricity Use
The short answer
Weather changes how much electricity a building uses, and meteorologists measure it in degree days: how far each day's average temperature falls below or rises above 65°F. Ohio cities typically log about 4,900–5,600 heating degree days and 950–1,160 cooling degree days a year. To judge whether a change in your bill came from weather or from your operations, weather-normalize your usage with a simple regression against degree days. Weather also has a cost beyond kWh: your load on a few hot summer weekday afternoons sets your capacity tag, and with it a year of capacity costs.
For winter price-spike exposure on index contracts, see extreme weather preparedness. For an operating checklist during cold snaps, see emergency planning for cold snaps. For keeping the business running through outages, see energy continuity planning.
Degree days in Ohio
The National Weather Service defines degree days against a 65°F base. A day averaging 80°F adds 15 cooling degree days (CDD); a day averaging 25°F adds 40 heating degree days (HDD). Annual normals for 1991–2020:
| Station | Heating degree days | Cooling degree days |
|---|---|---|
| Toledo | 5,641 | 1,019 |
| Cleveland | 5,516 | 947 |
| Columbus | 5,233 | 1,068 |
| Dayton | 5,149 | 1,154 |
| Cincinnati (CVG airport) | 4,892 | 1,160 |
Two things follow. First, Ohio has roughly four to six times as many heating degree days as cooling degree days, so buildings with electric heat — heat pumps, electric resistance, electric unit heaters in warehouses — are far more weather-sensitive in winter than gas-heated buildings. Second, northern Ohio needs more heating and southern Ohio more cooling, so the same building type will have a different seasonal shape in Toledo than in Cincinnati.
How weather shows up in your bills
- Gas-heated buildings usually show a summer electric peak (cooling) and a smaller winter bump (fans, pumps, lighting in shorter days).
- Electrically heated buildings often peak in January or February.
- Baseload — refrigeration, IT, process loads, lighting — doesn't respond to weather and shows up as the floor in spring and fall.
- Humidity adds cooling load on muggy days, which degree days alone don't capture. Expect some scatter in summer months.
- Billing periods rarely match calendar months. Match each bill's read dates to the degree days in that exact period.
Weather-normalizing your usage
Normalization separates "it was a hot summer" from "something changed in the building." A basic version takes an afternoon in a spreadsheet:
- Collect 24 months of bills with read dates and kWh for each account.
- Get degree days for the nearest station for each billing period. ENERGY STAR Portfolio Manager's free degree-day calculator uses NOAA data and a 65°F base.
- Divide kWh and degree days by the number of days in each period, so short and long bills compare fairly.
- Run a regression of daily kWh against daily CDD (and HDD, if you heat electrically). The intercept is your baseload; the slope is kWh per degree day.
- Apply normal-year degree days to the equation to get weather-normalized annual use. Compare that year over year.
Illustrative example: suppose the regression for a gas-heated retail store gives daily kWh = 850 + 9 × daily CDD. A July billing period of 30 days with 300 CDD predicts 30 × 850 + 9 × 300 = 28,200 kWh. If the actual bill shows 31,500 kWh, about 3,300 kWh is unexplained by weather — worth checking controls, schedules or a failing unit.
ENERGY STAR Portfolio Manager does this automatically: it runs a series of regressions against 65°F degree days using NOAA weather data and reports weather-normalized use against a climate normal (currently 2006–2020 averages). A fit with a low R² means weather isn't explaining much of the variation — often a sign that operations changed. For turning this into savings verification, see performance tracking mistakes.
Summer peaks and your capacity tag
Your capacity tag is based on your load during PJM's five highest summer peaks — the highest non-holiday weekday daily peaks between June 1 and September 30. Those almost always fall on hot, humid weekday afternoons. The tag resets each June 1 and is multiplied by the PJM capacity price, which is about $120 per kW a year at the 2026/27 price of $329.17/MW-day.
So weather affects cost twice:
| Effect | When | Cost impact |
|---|---|---|
| More kWh for cooling | Every hot day | Energy charges this month |
| Higher monthly peak kW | Hottest day of the month | Demand charges this month |
| Load during PJM's summer peaks | Five hours each summer | Capacity cost for 12 months from the next June 1 |
Cutting load during likely PJM peak hours — pre-cooling in the morning, shifting batch processes, raising setpoints for a few hours — can lower the tag without affecting total kWh much. See capacity tags explained and the PLC operations guide.
Operating for Ohio's seasons
- Schedule HVAC maintenance in April and October, before the cooling and heating seasons.
- Pre-cool on forecast peak days, then let temperatures drift during the afternoon peak.
- Use controls that follow weather, not fixed calendars — see smart building technology.
- Seal dock doors and envelopes before winter; see winterizing Ohio businesses.
- Stagger restarts after cold nights or outages so electric heat and motors don't all start together.
FAQ
What is a heating degree day?
It's the number of degrees a day's average temperature falls below 65°F. A day averaging 30°F counts as 35 heating degree days.
How do I weather-normalize my electricity usage?
Regress daily kWh for each billing period against daily heating and cooling degree days, then apply normal-year degree days to the resulting equation. ENERGY STAR Portfolio Manager does this for you.
Why does a hot summer raise next year's electricity costs?
Your capacity tag is set from your load during PJM's five highest summer peaks, and that tag sets your capacity cost for the 12 months starting the next June 1.
Does weather affect fixed-price contract customers?
It changes your usage, demand charges and capacity tag, but not your contracted supply price per kWh.
Sources
- NOAA NCEI U.S. Climate Normals 1991–2020: https://www.ncei.noaa.gov/products/land-based-station/us-climate-normals
- National Weather Service, heating and cooling degree days: https://www.weather.gov/key/climate_heat_cool
- ENERGY STAR Portfolio Manager Technical Reference, Climate and Weather: https://portfoliomanager.energystar.gov/pdf/reference/Climate%20and%20Weather.pdf
- PJM Manual 19 (five coincident peaks): https://www.pjm.com/-/media/DotCom/documents/manuals/m19.ashx