--- title: "Heating and cooling degree days for HVAC reviews" description: "Calculate heating and cooling degree days from sample temperatures. Match base, units, and periods before comparing weather with HVAC call history." canonical: "https://scalewithsearch.com/articles/hvac-heating-cooling-degree-days-base-period" --- ## Site navigation - [Scale With Search](https://scalewithsearch.com/) - Services - Services - [AI systems](https://scalewithsearch.com/ai-systems) - [Site build](https://scalewithsearch.com/work#site-build) - [Whole website fix](https://scalewithsearch.com/work#whole-website-fix) - [Content library with SEO](https://scalewithsearch.com/work#content-library) - [Working session](https://scalewithsearch.com/audit) - Start here - [Send your brief](https://scalewithsearch.com/work#send-your-brief) - [Example scope](https://scalewithsearch.com/work#review-the-example-scope) - [Prices and terms](https://scalewithsearch.com/work#prices-and-terms) - Industries - Real estate - [Real estate agents and teams](https://scalewithsearch.com/for/real-estate) - [Platforms, ownership, and IDX](https://scalewithsearch.com/for/real-estate/real-estate-website-platforms-ownership-idx) - [Search, content, and AI](https://scalewithsearch.com/for/real-estate/real-estate-search-content-ai) - [Inquiries, campaigns, and handoffs](https://scalewithsearch.com/for/real-estate/real-estate-website-inquiries-campaigns-handoffs) - [Buyer, seller, and local pages](https://scalewithsearch.com/for/real-estate/real-estate-buyer-seller-local-resources) - [Rules, privacy, and trust](https://scalewithsearch.com/for/real-estate/real-estate-website-rules-privacy-trust) - Browse by business - [Trades and home services](https://scalewithsearch.com/for/#group-trades) - [Health, wellness, and animal care](https://scalewithsearch.com/for/#group-practices) - [Law, finance, and IT](https://scalewithsearch.com/for/#group-professional) - [Marketing and SEO agencies](https://scalewithsearch.com/for/#group-agencies) - [Shops and manufacturers](https://scalewithsearch.com/for/#group-manufacturing) - [Restaurants, shops, studios, and nonprofits](https://scalewithsearch.com/for/#group-local-services) - Chiropractic practices - [Chiropractic and wellness practices](https://scalewithsearch.com/for/chiropractic-and-wellness-practices) - [Chiropractic and physical therapy clinics](https://scalewithsearch.com/for/chiropractic-and-physical-therapy-clinics) - [All industries](https://scalewithsearch.com/for/) - Resources - Free tools - [AI readiness check](https://scalewithsearch.com/check) - [Free tools](https://scalewithsearch.com/tools/) - [Free Starter Kit](https://scalewithsearch.com/kit/business-memory-starter-kit.zip) - Guides - [AI-native library](https://scalewithsearch.com/ai-native) - [Industry intelligence](https://scalewithsearch.com/intelligence) - [Office job guides](https://scalewithsearch.com/guides/) - [Business memory](https://scalewithsearch.com/articles/business-memory-for-ai-agents-guide) - [Agent governance](https://scalewithsearch.com/articles/ai-agent-governance-guide-small-business) - [Migration and ownership](https://scalewithsearch.com/articles/leaving-vendor-ai-memory-guide) - Articles - [All articles](https://scalewithsearch.com/articles/) - [What changed](https://scalewithsearch.com/changes/) - About - Evidence - [Proof](https://scalewithsearch.com/proof) - Scale With Search - [About](https://scalewithsearch.com/about) - [How it works](https://scalewithsearch.com/how-it-works) # Heating and cooling degree days: read the base before an HVAC capacity review Before comparing a busy service week with a quiet one, write down what the weather number measures. A degree-day total needs its base temperature, units, location, and observation period. Without those labels, two correct numbers can support an incorrect comparison. For an HVAC operations manager, the useful first output is a weather-context worksheet. It explains the calculation and places approved call history beside comparable weather observations. The manager can then decide which questions need investigation before the next capacity review. The [HVAC contractor guide](/for/hvac-contractors) covers preparation from approved business records. The [HVAC intelligence overview](/intelligence/hvac-contractors) places weather context beside other research functions. This article handles the arithmetic and period matching needed before interpreting a relationship with calls. ## Start with a named base and daily mean The [EIA degree-day guide](https://www.eia.gov/energyexplained/units-and-calculators/degree-days.php) uses a 65°F base and calculates the daily mean from the high and low temperatures. Add the high and low, then divide by two. The base is the reference used in that calculation, not a thermostat instruction. Keep the daily high, daily low, and resulting mean in Fahrenheit for this example. Write the chosen base beside them. Do not combine Celsius temperatures with a Fahrenheit base or describe a degree-day total as an outdoor temperature. A daily mean does not preserve the sequence of temperatures within the day. In a synthetic example, a high of 80°F and low of 50°F produce a mean of 65°F. The same mean follows from a high of 70°F and low of 60°F. Retain the inputs when that distinction matters to your review. Use the publisher's stated calculation for a published series. The simple arithmetic here explains the concept. It does not establish that a particular downloaded product uses your chosen station, period boundary, or processing method. Those details require that product's documentation. ## Keep heating and cooling in separate columns For this base-65 example, calculate heating degree days as the positive amount by which the mean falls below 65°F. Calculate cooling degree days as the positive amount by which it exceeds 65°F. If the mean equals the base, both are zero. The [CPC explanation of degree-day summaries](https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/cdus/degree_days/ddayexp.shtml) describes separate heating and cooling accumulation from daily means. Its cooling example also assigns zero to a day at the base. Use that separation throughout your worksheet. In formula form, the proposed worksheet uses HDD = max(65 minus mean, 0) and CDD = max(mean minus 65, 0). Label the results Fahrenheit degree days, base 65°F. A negative difference does not become a negative entry in either daily column. Do not subtract the cooling total from the heating total. That would create a different quantity and hide both components. A period containing cold and warm days needs two totals, even if their numerical difference happens to be small. Choose column labels that survive copying into a meeting note. “Heating degree days, base 65°F” carries the reference with the number. “Weather score” leaves the next reader to guess which measure and direction the author intended. ## Work through five synthetic days Every value in the following table is invented. Days 1 through 5 are consecutive, complete days at one fictional station. They demonstrate the arithmetic only. They do not represent a city, current weather, or a service forecast. | Synthetic day | High, °F | Low, °F | Mean, °F | HDD, base 65°F | CDD, base 65°F | | --- | --- | --- | --- | --- | --- | | Day 1 | 58 | 38 | 48 | 17 | 0 | | Day 2 | 72 | 48 | 60 | 5 | 0 | | Day 3 | 80 | 50 | 65 | 0 | 0 | | Day 4 | 92 | 64 | 78 | 0 | 13 | | Day 5 | 86 | 60 | 73 | 0 | 8 | | Five-day total | Not applicable | Not applicable | Not summed | 22 | 21 | For Day 1, the mean is (58 + 38) / 2 = 48°F. The heating entry is 65 minus 48, or 17. For Day 4, the mean is 78°F. The cooling entry is 78 minus 65, or 13. Add the five heating entries to obtain 22 HDD. Separately, add the five cooling entries to obtain 21 CDD. Do not add the mean temperatures to create either total. Preserve the five rows so another reviewer can reproduce the result. Day 3 deserves attention because its result is zero in both columns. That outcome follows from the daily mean and chosen base. It does not establish that no customer used equipment or that no service call could occur that day. If Day 2 were missing, report four available days and one missing day. Do not replace the blank with zero and keep the “complete five-day” label. A verified replacement observation would need its own source and acceptance note. ## Match the period before comparing totals Suppose another entirely synthetic five-day period has 30 HDD and 12 CDD at the same fictional station and base. The first period has eight fewer HDD and nine more CDD. Those statements compare the two weather measures separately. Write both start dates, end dates, and included-day counts before showing that comparison. Define whether the end date is included. An analyst should not need to reconstruct your date convention from a spreadsheet formula or chart axis. Keep a three-day partial week separate from a complete seven-day week. A daily average may answer a different question, but label it as an average. Do not quietly replace one period's total with an average while keeping the same column heading. Likewise, distinguish a fixed calendar period from a season-to-date accumulation. CPC's [summary definitions](https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/cdus/degree_days/ddayexp.shtml) use different accumulation years: July through June for heating and January through December for cooling. Check the selected product before comparing a cumulative field with a weekly total. For a business review, choose dates that match the question and then document that choice. A Monday-through-Sunday call report needs weather observations covering those dates. If the available weather product covers different dates, show the mismatch and hold the direct comparison. ## Read the product edition and comparison field A directory can contain several generations of products. The [CPC degree-day page](https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/cdus/degree_days/) distinguishes updated population-weighted products from older links with different population and normal periods. Select the actual file and its documentation together. A total, a departure from normal, and a departure from last year answer different questions. The legacy [CPC field explanation](https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/cdus/degree_days/ddayexp.shtml) identifies those as separate fields. Copy the exact field label into your source note instead of renaming them all “degree days.” If your worksheet uses a normal comparison, record the reference years stated for that product. If it uses a prior-year comparison, record the prior period. A retrieval date describes when you obtained the evidence. It does not replace the dates the evidence covers. Treat geography as another matching requirement. A station observation and a population-weighted region describe different scopes. The companion [population-weighted degree-day guide](/articles/hvac-population-weighted-degree-days-local-context) explains how to choose between them for a territory discussion. ## Put approved call history beside the weather Use the following as a proposed internal review method, rather than an established prediction model. Ask the operations manager to choose an approved call category, service zone, and date field. Record those choices before comparing any counts. For example, incoming repair requests dated by receipt and completed visits dated by completion are different business measures. Keep them separate in the proposed worksheet. Do not switch between them midway through a comparison to create a clearer relationship. Use only records your company has approved for this purpose. A meeting worksheet can use aggregate counts without customer names, contact details, or address-level notes. Keep access to the underlying service records within the company's existing permissions. Place one row per matched period beside the weather totals. Include available-day counts, source labels, call-category definitions, and known operating changes supplied by the manager. A changed service territory or intake process belongs in the interpretation note. Start the conclusion with what you observed. For example: “In these selected periods, this call category was higher when CDD was higher.” If that pattern exists, describe its sample and limits. It remains uncalibrated until a separate evaluation supports a specific forecasting use. Do not turn the observed association into an instruction to add technicians, change shifts, or promise appointment availability. Dispatch and capacity decisions need current operating evidence and the responsible manager's judgment. This worksheet supplies one context layer for that discussion. ## Resolve a mismatched business calendar Consider a proposed review in which the weather worksheet covers five complete calendar days. The business export covers five operating days across a weekend. Although both files contain five rows, they do not describe the same dates. Record that mismatch before discussing the difference in calls. Ask the manager which question the comparison should answer. If the question concerns incoming requests during the weather period, prepare the approved request count for those dates. If the question concerns work completed on operating days, label that measure and use the matching dates. Preserve the original exports while preparing the aligned view. Write down which dates entered the comparison and which were excluded. A later reviewer should be able to distinguish a deliberate calendar choice from a missing observation or an accidental filter. If alignment is unavailable, keep the weather total as background context. State the unresolved date mismatch in the meeting note and assign its follow-up. The team can still discuss the operating record without presenting an unsupported numerical relationship. Before repeating the review, have the manager accept the date convention in writing. Carry that convention into the next worksheet. If the question changes, describe the new convention instead of treating the two views as one continuous comparison. ## Use a review worksheet that carries its assumptions Before the meeting, prepare the following fields. These are editorial recommendations, not required publisher fields. Leave a field unresolved when the available documentation cannot support it. | Review field | What to record | | --- | --- | | Review question | The specific comparison the manager wants to discuss | | Weather series | Publisher, product name, file or page URL, and location identifier | | Calculation | Heating or cooling, Fahrenheit degree days, and base temperature | | Observation period | Inclusive start and end, expected days, and available days | | Comparison | Other period, prior year, or named normal reference period | | Product status | Edition, revision statement, and retrieval date | | Business measure | Approved call category, zone, date field, and count convention | | Open question | Mismatch, missing observation, or explanation requiring review | | Decision record | Reviewer, date, accepted interpretation, and follow-up owner | Ask a second reader to reproduce one daily row and both period totals. Then ask that reader to identify the source, period, and base without opening another file. An unexplained label should be corrected before the worksheet enters the meeting. Retain the manager's accepted interpretation with the evidence. The [business memory guide](/articles/business-memory-for-ai-agents-guide) describes keeping decisions and corrections available for later work. For this review, that means preserving why the comparison was accepted, limited, or rejected. Bring Scale With Search one weather-context worksheet, the approved call-count definition, and the manager who will review it. The written scope can define the source handling and handoff for that bounded function. [Request a written scope](/work) Source note: EIA definitions and CPC degree-day documentation were reopened on 2026.10.28. CPC's older explanation describes legacy fields; the directory identifies newer product families. No published weather observation is quoted here. All example temperatures, totals, and review procedures are synthetic or editorial. Continue the website review: [AI-native HVAC contractors: the first functions to build](/articles/ai-native-hvac-contractors-first-functions); [HVAC After-Hours Website: What Does 24/7 Mean?](/articles/hvac-after-hours-website-availability); [HVAC contractor AI rules: data, approvals, and spend](/articles/hvac-ai-rules-data-approvals-spend); [HVAC building comparisons: choose a peer group and explain its limits](/articles/hvac-building-energy-peer-group-comparison); [HVAC Financing Pages: Check the Advertised Terms](/articles/hvac-financing-website-advertising-review); [Heat Pump Website Claims: Ratings and Bill Savings](/articles/hvac-heat-pump-efficiency-website-claims); [HVAC Project Pages: Show the Work Without Guessing](/articles/hvac-installation-project-pages); [HVAC Maintenance Plan Pages: Explain What Is Included](/articles/hvac-maintenance-plan-website-page); [HVAC marketing: connect your website and local profile](/articles/hvac-marketing-website-local-plan); [Population-weighted degree days: choose regional context without replacing local weather](/articles/hvac-population-weighted-degree-days-local-context); [HVAC Refrigerant Copy: Remove Blanket Replacement Claims](/articles/hvac-refrigerant-website-copy-update); [HVAC Service Pages: Separate Repair and Installation](/articles/hvac-repair-installation-service-pages); [HVAC Search Console Report: Clicks and Inquiries](/articles/hvac-search-console-inquiry-report); [HVAC Warranty Pages: Separate Equipment and Labor](/articles/hvac-warranty-website-manufacturer-labor); [HVAC Websites in AI Answers: Fix the Source Facts](/articles/hvac-website-facts-ai-search-answers); [HVAC Website Credentials: Licenses and Certifications](/articles/hvac-website-licenses-certifications); [Site and source EUI: read building energy data before an HVAC assessment](/articles/site-source-eui-hvac-building-assessment). [HVAC contractors](/for/hvac-contractors): website and search resources. ## Related: HVAC contractors - [HVAC Project Pages: Show the Work Without Guessing](/articles/hvac-installation-project-pages) - [HVAC Maintenance Plan Pages: Explain What Is Included](/articles/hvac-maintenance-plan-website-page) - [HVAC marketing: connect your website and local profile](/articles/hvac-marketing-website-local-plan) ---- ```text .|########||. .|########||. .|########||. |##||. .||##|. |##||. .||##|. |##||. .||##|. |#|. .|#|. |#|. .|#|. |#|. .|#|. |#| |#| |#| |#| |#| |#| .#| |#. .#| |#. .#| |#. .#. .#| .#. .#| .#. .#| |#. .#| |#. .#| |#. .#| |# ...... #| |# ...... #| |# ...... #| .# ||#########| #| .# ||#########| #| .# ||#########| #| .#. |######||######|. .#. .#. |######||######|. .#. .#. |######||######|. .#. #. .##|###|##|#|######| .# #. .##|###|##|#|######| .# #. .##|###|##|#|######| .# || |##|#||||||||||||#||#| || || |##|#||||||||||||#||#| || || |##|#||||||||||||#||#| || # |#||||||||||||||||||||#| #. # |#||||||||||||||||||||#| #. # |#||||||||||||||||||||#| #. || |#||||||||||||||||||||||#| || || |#||||||||||||||||||||||#| || || |#||||||||||||||||||||||#| || # .#||||||||||||||||||||||||#| # # .#||||||||||||||||||||||||#| # # .#||||||||||||||||||||||||#| # || ....|||#||||||##|#|||#|#||##||||....|. || || ....|||#||||||##|#|||#|#||##||||....|. || || ....|||#||||||##|#|||#|#||##||||....|. || #. . ....|# ....#||| ||| .#||| ....#. .# #. . ....|# ....#||| ||| .#||| ....#. .# #. . ....|# ....#||| ||| .#||| ....#. .# # . ||||#| .#####|| . .#| .#||| ||||# #. # . ||||#| .#####|| . .#| .#||| ||||# #. # . ||||#| .#####|| . .#| .#||| ||||# #. .| ||||| #. |#|||||. || #. |#||. .||||| || .| ||||| #. |#|||||. || #. |#||. .||||| || .| ||||| #. |#|||||. || #. |#||. .||||| || || |.... #. ....|#. |. ...|. ....|| || || |.... #. ....|#. |. ...|. ....|| || || |.... #. ....|#. |. ...|. ....|| || #. .||||||##||||||##||####|||||||#||||||#| .# #. .||||||##||||||##||####|||||||#||||||#| .# #. .||||||##||||||##||####|||||||#||||||#| .# # .||####|###########################|. # # .||####|###########################|. # # .||####|###########################|. # # .#||||||.#.|| # |. ..# #| #|||||#| # # .#||||||.#.|| # |. ..# #| #|||||#| # # .#||||||.#.|| # |. ..# #| #|||||#| # # .#|||||| .. |# ## |#| ...#|#|||#| # # .#|||||| .. |# ## |#| ...#|#|||#| # # .#|||||| .. |# ## |#| ...#|#|||#| # # .#|||#|# .# .#| #| ##|.#..#|||||#| # # .#|||#|# .# .#| #| ##|.#..#|||||#| # # .#|||#|# .# .#| #| ##|.#..#|||||#| # # .#||||||############|######|||||#| # # .#||||||############|######|||||#| # # .#||||||############|######|||||#| # # |...||#||||||#||||#|#||||||#|||||#||| |.| # # |...||#||||||#||||#|#||||||#|||||#||| |.| # # |...||#||||||#||||#|#||||||#|||||#||| |.| # #. .. ||||# .|||##|. |#| .|| || .|||#. #| # .# #. .. ||||# .|||##|. |#| .|| || .|||#. #| # .# #. .. ||||# .|||##|. |#| .|| || .|||#. #| # .# || | ...|| ...##| | #| .|. |. ##### .. .| || || | ...|| ...##| | #| .|. |. ##### .. .| || || | ...|| ...##| | #| .|. |. ##### .. .| || || ||||| || ||||#| . |. |. |#. ||||| |#| || || || ||||| || ||||#| . |. |. |#. ||||| |#| || || || ||||| || ||||#| . |. |. |#. ||||| |#| || || .# |.....#|....|#.||||.|||##.|#|....||.#||.#. #. .# |.....#|....|#.||||.|||##.|#|....||.#||.#. #. .# |.....#|....|#.||||.|||##.|#|....||.#||.#. #. #.|||||||#############################| ||| .# #.|||||||#############################| ||| .# #.|||||||#############################| ||| .# || ##||#||#||||||#||#||#||#||##. || || ##||#||#||||||#||#||#||#||##. || || ##||#||#||||||#||#||#||#||##. || # .#|||||||||#||#|||||||||||#| # # .#|||||||||#||#|||||||||||#| # # .#|||||||||#||#|||||||||||#| # || |#||||||||||||||||||||||#| || || |#||||||||||||||||||||||#| || || |#||||||||||||||||||||||#| || .# |#||||||||||||||||||||#| #. .# |#||||||||||||||||||||#| #. .# |#||||||||||||||||||||#| #. || |#||||||||||||||||||#| || || |#||||||||||||||||||#| || || |#||||||||||||||||||#| || #. .######|#|#########| .# #. .######|#|#########| .# #. .######|#|#########| .# .#. |#####||||#####| .#. .#. |#####||||#####| .#. .#. |#####||||#####| .#. |# ||########|| #. |# ||########|| #. |# ||########|| #. |# ...... #| |# ...... #| |# ...... #| |#. .#| |#. .#| |#. .#| |#. .#. |#. .#. |#. .#. .#| |#. .#| |#. .#| |#. |#| |#| |#| |#| |#| |#| .|#|. .|#|. .|#|. .|#|. .|#|. .|#|. |##||. .||##| |##||. .||##| |##||. .||##| .||########||. .||########||. .||########||. 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