{"uid":"cap_ChgwhGlJptJACtQHu8rIO","slug":"hvac-fan-affinity-laws-calculator-34de7491","name":"HVAC Fan Affinity Laws Calculator","description":"Fan affinity laws: new airflow, pressure and power after a speed change (flow ~ N, pressure ~ N^2, power ~ N^3).","url":"https://hvac-calc.x402tookit.com/fan-laws?utm_source=zero.xyz","method":"GET","headers":{},"bodySchema":{"type":"object","$schema":"https://json-schema.org/draft/2020-12/schema","required":["input"],"properties":{"input":{"type":"object","required":["type","method"],"properties":{"type":{"type":"string","const":"http"},"method":{"enum":["GET"],"type":"string"},"queryParams":{"type":"object","required":["rpmFrom","rpmTo"],"properties":{"cfm":{"type":"number","description":"Current airflow in CFM"},"power":{"type":"number","description":"Current shaft power (hp or kW)"},"rpmTo":{"type":"number","description":"New fan speed, same unit"},"rpmFrom":{"type":"number","description":"Current fan speed (rpm or hertz)"},"staticPressureInWg":{"type":"number","description":"Current static pressure in in. wg"}}}},"additionalProperties":false},"output":{"type":"object","required":["type"],"properties":{"type":{"type":"string"},"example":{"type":"object","properties":{"asOf":{"type":["null","string"]},"newCfm":{"type":["null","number"]},"source":{"type":["null","string"]},"reasons":{"type":["array","null"],"items":{"type":"string"}},"summary":{"type":["null","string"]},"verdict":{"type":["null","string"]},"degraded":{"type":["boolean","null"]},"newPower":{"type":["null","number"]},"flowRatio":{"type":["null","number"]},"disclaimer":{"type":["null","string"]},"notChecked":{"type":["array","null"],"items":{"type":"string"}},"powerRatio":{"type":["null","number"]},"speedRatio":{"type":["null","number"]},"pressureRatio":{"type":["null","number"]},"newStaticPressureInWg":{"type":["null","number"]}}}}}}},"responseSchema":null,"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.02","displayCostAsset":"USDC","priceDynamic":false,"priceHint":null,"priceStatus":"priced","priceSource":"probe","requiresHandshake":false,"reviewCount":0,"rating":{"score":"0.00","successRate":"0.00","reviews":0,"stars":null,"state":"unrated"},"availabilityStatus":"unknown","priceObserved":null,"sessionDeposit":null,"pricing":{"kind":"static","summary":"$0.02/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.02","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.02","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_JS4wfA0mrAjeoyBXpUVIT","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.02","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"Calculates new airflow (CFM), static pressure, and shaft power after a fan speed change using the fan affinity laws (flow ∝ N, pressure ∝ N², power ∝ N³).","exampleAgentPrompt":"My supply fan is currently running at 1200 RPM delivering 5000 CFM at 1.5 in. wg static pressure and consuming 3 hp — if I slow it down to 900 RPM with a VFD, what will the new airflow, pressure, and power be?","exampleUseCases":[{"title":"VFD energy savings estimation","prompt":"Our air handler fan runs at 1800 RPM using 10 hp. If we install a VFD and drop it to 1440 RPM, calculate the new CFM, static pressure, and shaft power so I can estimate the energy savings."},{"title":"Fan speed increase for added cooling load","prompt":"Our current fan runs at 850 RPM, moving 3200 CFM at 0.8 in. wg. We need to bump it to 1050 RPM to handle a new load — what will the airflow and pressure be at the higher speed?"},{"title":"Commissioning fan performance verification","prompt":"During commissioning I measured 4500 CFM at 1200 RPM with 2.0 in. wg static pressure and 5 hp shaft power. The design calls for 1350 RPM — use the fan affinity laws to tell me what airflow, pressure, and power I should expect at that design speed."}],"resultDescription":"Returns the speed ratio (N2/N1), flow ratio, pressure ratio, and power ratio, along with computed new airflow (newCfm), new static pressure (newStaticPressureInWg), and new shaft power (newPower), plus a human-readable summary and any applicable disclaimer.","failureModes":["Missing required rpmFrom or rpmTo parameters returns an error","Zero or negative RPM values may produce invalid ratios","If optional cfm, staticPressureInWg, or power are omitted, corresponding new values will be null","Extremely large speed ratios may produce physically unrealistic results without warning"],"whenToPreferThis":"Use this endpoint when you need a fast, deterministic fan affinity law calculation given current and new fan speeds — ideal for VFD sizing, energy audits, commissioning checks, or any HVAC workflow where fan performance scaling is needed without running full simulation software.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-10-29T13:11:21.248Z","isFirstParty":false,"canonicalSlug":"hvac-fan-affinity-laws-calculator-34de7491"}