Compare a Surface Scenario with an Explicit Over-Water Dewpoint Approximation — Free
Room humidity and a cold surface are separate measurements. Keep the air inputs, estimated dewpoint and surface scenario together instead of turning one RH percentage into a building verdict.
The proof surface
Ventilation run-time arithmetic does not estimate dew point from entered temperature/humidity or compare a separately measured surface temperature.
InputAir-sample code | air temperature Celsius | relative humidity percent; scenario surface temperature (°c)
Rare deviceVentilation run-time arithmetic does not estimate dew point from entered temperature/humidity or compare a separately measured surface temperature.
Output artifactSmallest scenario surface-minus-estimated-dewpoint margin plus complete labeled working
Cost$0 local core · no account, card, paid key or subscription · filing proposal has no checkout
Sample, not your facts: Invented records: Cedar indoor sample | 20 | 50. Scenario surface temperature (°C) = 12; expected Smallest scenario surface-minus-estimated-dewpoint margin: 2.730736 °C surface-minus-dewpoint margin. These are not quotations, verified observations or personal evidence.
Before using the condensation-margin psychrometric card
Use measured or explicitly hypothetical indoor air inputs and one clearly stated surface-temperature scenario. This approximation accepts air from 0 through 50 °C and RH from 0.1 through 100 percent; it is deliberately bounded and over water, not a universal meteorological model. The surface setting can range from −20 through 50 °C, but negative surfaces do not turn this into a frost prediction. The app has no sensor, weather feed, thermal camera or building inspection. A positive margin cannot rule out local condensation, mold, leakage or an unsafe room, and a negative margin does not prove those conditions occurred. Actual damp or health concerns need qualified investigation.
Why the flat version breaks
Relative humidity alone becomes a condensation claim
RH depends on air temperature, and condensation concerns the local surface as well. Comparing one percentage with a generic threshold hides both relationships. This card estimates a dewpoint from the air pair and compares the separately entered surface scenario. It intentionally has no compliance, comfort or healthy-home badge.
Zero humidity is passed through the logarithm
ln(0) cannot produce a finite dewpoint under this model. Rather than manufacturing a very low number, the app rejects zero and asks for a valid source measurement within its stated range. The preserved input and previous result make the failure actionable. A corrected number must come from evidence or an explicit scenario, not an arbitrary tiny replacement chosen to make the calculator run.
An approximation certifies a real building
The formula omits sensor uncertainty, airflow, local gradients, materials, liquid water sources and inspection evidence. It is not an assessment of mold or a prescription for heating or ventilation. Even a positive margin may miss a colder local surface. Seek qualified investigation for actual concerns and keep the over-water approximation language in any shared or exported reading.
How to work the condensation-margin psychrometric card
Record the air sample convention
Use a neutral room/time code and enter air temperature in Celsius plus RH as a percentage. These should describe the same air sample, not readings from different times selected to get a preferred result. The tool rejects zero RH because the logarithm would be undefined, and refuses values outside its stated indoor approximation bounds. It does not correct calibration or locate a sensor. Keep device, time and local conditions in the original record rather than sharing identifying home details.
Separate the surface scenario from air temperature
Enter the measured or hypothetical surface temperature in the setting. Do not substitute room air temperature unless that is the scenario you intentionally want to compare. The same surface value is applied to every row. If each room has a different measured surface, run separate source sets or compare them with a model designed for per-row surfaces. The card names the common setting so it cannot silently imply more measurements than were supplied.
Apply the stated logarithmic approximation
Let a = 7.5 ln(10), b = 237.3 °C, T be entered air temperature and h be RH divided by 100. Compute g = ln(h) + aT/(b+T), then estimated dewpoint Td = bg/(a−g). Margin is surface minus Td. The headline is the smallest row margin; row signs stay visible. A margin at or below zero receives an arithmetic review mark. The formula and coefficients are disclosed so another implementation can check the same convention rather than an unstated physical standard.
Treat the reading as a measurement question
Inspect inputs, estimated dewpoints and margins with the original observations. Do not infer health effects, appropriate ventilation equipment or a repair from this one calculation. Visible damp, water intrusion, electrical hazards or health concerns deserve appropriate professional help regardless of the displayed sign. A qualified building professional can assess surfaces and moisture sources, while a clinician handles health concerns. Copy or file the approximation boundary together with the numerical result.
What the condensation-margin psychrometric card keeps distinct
Question
Before
Check this working
Relative humidity alone becomes a condensation claim
RH depends on air temperature, and condensation concerns the local surface as well. Comparing one percentage with a generic threshold hides both relationships. This card estimates a dewpoint from the air pair and compares the separately entered surface scenario. It intentionally has no compliance, comfort or healthy-home badge.
Separate the surface scenario from air temperature
Zero humidity is passed through the logarithm
ln(0) cannot produce a finite dewpoint under this model. Rather than manufacturing a very low number, the app rejects zero and asks for a valid source measurement within its stated range. The preserved input and previous result make the failure actionable. A corrected number must come from evidence or an explicit scenario, not an arbitrary tiny replacement chosen to make the calculator run.
Apply the stated logarithmic approximation
An approximation certifies a real building
The formula omits sensor uncertainty, airflow, local gradients, materials, liquid water sources and inspection evidence. It is not an assessment of mold or a prescription for heating or ventilation. Even a positive margin may miss a colder local surface. Seek qualified investigation for actual concerns and keep the over-water approximation language in any shared or exported reading.
Treat the reading as a measurement question
The condensation-margin psychrometric card replaces this named manual reconciliation, not source verification or the responsible human's decision.
Run it on the samples, right here
FIRST-LOAD
HYPOTHESIS / PROTOTYPE — checkout unavailable. Calculation is local. A draft is saved automatically in this browser profile when storage is available; Reset to sample clears it. Optional Pro history stores only five summaries and has its own deletion control. State links encode your inputs and can remain in browser history, clipboard or recipients’ records; share only non-sensitive rows. Optional external AI formatting leaves this device. The required site analytics beacon reports page activity; shared URLs contain encoded inputs. Do not treat an encoded URL as private. The calculator has no input-collection endpoint.
Bounded over-water approximation only: no mold, health, condensation, frost or building-safety diagnosis and no repair prescription. Verify measurements and actual moisture concerns with a qualified building professional; take health concerns to a qualified clinician.
Data note: This condensation-margin psychrometric card calculates in the tab from Air-sample code | air temperature Celsius | relative humidity percent. No input-collection endpoint, AI request or file upload is built into it. Drafts may be saved locally; explicit input-state links and optional external formatting can disclose the records. Use non-sensitive codes and clear the draft when finished.
Go deeper: the companion app files the same reading as a index card with a stamped header
The article demo above runs without limits. The companion app keeps a local history, exports the rows as CSV, prints the condensation-margin psychrometric card reading, and holds your drafts on this device — one complete free app run; the proposed $4 one-time filing layer is not for sale.
Keep the complete condensation-margin psychrometric card answer free; optional filing proposes its boundary-preserving print, row-and-summary CSV and five local reading summaries. The $4 one-time prototype is not for sale; another calculation remains free in the article demo.
Bounded over-water approximation only: no mold, health, condensation, frost or building-safety diagnosis and no repair prescription. Verify measurements and actual moisture concerns with a qualified building professional; take health concerns to a qualified clinician.
What this is built on
Declared local method: Let a = 7.5 ln(10), b = 237.3 °C, T be entered air temperature and h be RH divided by 100. Compute g = ln(h) + aT/(b+T), then estimated dewpoint Td = bg/(a−g). Margin is surface minus Td. The headline is the smallest row margin; row signs stay visible. A margin at or below zero receives an arithmetic review mark. The formula and coefficients are disclosed so another implementation can check the same convention rather than an unstated physical standard.
Every sample code, measurement, date, price, fingerprint and scenario is invented. Artifact checks do not verify reader data, policies, actual files, tickets, votes or health/accessibility outcomes.
National Weather Service RH/dewpoint calculator and its linked formula notes, fetched 2026-10-01, describe the humidity/dewpoint relationship. This local card states its own bounded over-water coefficients and does not calculate wet-bulb temperature, station pressure or an inspection outcome.
Google’s official Gemini pricing page, fetched 2026-10-01, lists AI Studio access in its Free section, limited model access and free input/output tokens. Free-tier content may be used to improve products. Optional external formatting may require an account; limits/access can change. Manual local entry needs none. Do not send sensitive records.
Before: one humidity percentage seemed to decide a damp-room story. After: paired air observations, a separate surface scenario and an explicit approximation define a limited temperature margin.
Three worked readings, with different inputs
Sample A — typical inputs
Cedar indoor sample | 20 | 50
Setting: Scenario surface temperature (°C) = 12. Expected summary: 2.730736 °C surface-minus-dewpoint margin.
The stated over-water formula estimates dew point at about 9.269264 °C for air at 20 °C and 50 percent RH. An entered 12 °C surface scenario is about 2.730736 °C above that estimate. The positive model margin is not a building-safety or mold pass; sensor error, local surface conditions, moisture sources and the approximation’s limitations have not been assessed.
Setting: Scenario surface temperature (°C) = 12. Expected summary: -3.119667 °C surface-minus-dewpoint margin.
Estimated dewpoints are about 15.119667 and 12.940200 °C. The common 12 °C surface scenario gives margins of −3.119667 and −0.940200 °C; the headline is the smaller, more negative margin. It compares one supplied surface scenario with two air observations, not two independently measured surface temperatures. Both nonpositive margins are review prompts, not confirmed condensation observations.
Sample C — boundary convention
Saturated-air boundary | 12 | 100
Setting: Scenario surface temperature (°C) = 12. Expected summary: 0 °C surface-minus-dewpoint margin.
At 100 percent RH, the formula’s estimated dewpoint equals the entered air temperature, 12 °C. The matching 12 °C surface has a zero margin, included in the nonpositive review mark. Equality is not nudged into a safe-looking positive result by decimal rounding. The calculation is an over-water approximation, not a frost-point model or a verified observation of liquid on a real surface.
Optional AI formatting, never the calculation
Manual entry completes this condensation-margin psychrometric card for free without signup. If available to you, the free AI Studio interface linked in the sources may format fictional or non-sensitive notes; external access may require an account. No API key or AI call is built into this tool. Free-tier content may be used to improve products. Review each cell and transcribe it to the labeled row schema; do not paste the JSON object into the row box.
Format only these fictional or non-sensitive notes for a condensation-margin psychrometric card. Return strict JSON shaped as {"rows": [{"label": "string", "cells": ["string", "string"]}], "setting": "string"}. The columns are Air-sample code | air temperature Celsius | relative humidity percent; the setting is Scenario surface temperature (°C). Keep all supplied strings and quantities exactly; do not calculate, infer missing entries, invent dates or add advice. If any required value is missing, return an empty rows array and ask me for it separately. I will verify every cell against my source and manually transcribe rows using vertical bars before running the local calculator.
An AI response is not executed, fetched or trusted as a result. Missing values remain questions; the strict local parser checks the rows you actually enter.