---
title: "About: Free Heating & Cooling Calculators | Warm Window"
description: "What Warm Window is, how its heater, air conditioner, heat loss, dew point and heating cost calculators work, and where their numbers come from."
url: https://warmwindow.homes/about/
---

About

# About Warm Window

Warm Window is a small set of free calculators for keeping a room comfortable: how big a heater or air conditioner it needs, where its heat escapes, why its windows run wet and what heating it costs.

## How the calculators work

Everything is worked out by JavaScript in your browser as you type. Nothing you enter is sent anywhere, and the pages keep working if your connection drops after they have loaded. The only thing stored on your device is your choice of light or dark theme and of metric or imperial units.

Each calculator shows its working: the formula, the values it used and the sources they came from. Where a figure is a typical value rather than a measurement of your home, such as a U-value or an air change rate, the page says so and lets you type your own.

## What the numbers are for

The results are estimates for planning and for checking quotes. They are not a heating or cooling design. For a whole-home boiler, heat pump or central air system, ask for a room-by-room survey by a qualified installer (EN 12831 in Europe, ACCA Manual J in North America), and follow the manufacturer's instructions for any heater or appliance.

## Sources

The calculators rely on published data: the ENERGY STAR room air conditioner sizing chart, U-values from the UK's RdSAP 10 and SAP 10.2 methods and Approved Document L, design temperatures and degree-days reproduced by MCS from CIBSE and the Met Office, fuel energy contents from the US Energy Information Administration and Forest Research, and the Alduchov and Eskridge form of the Magnus formula for dew point. Each page lists the documents it uses.

## Who runs it

Warm Window is an independent site, one of a family of small tool sites listed in the footer. It is not linked to any energy supplier, installer or manufacturer, and it does not sell anything. Found a mistake? The sources are linked on every page so you can check the figures yourself.

[Open the room heater calculator](https://warmwindow.homes/)