About WhatSize

WhatSize works out what capacity of home equipment you need — air conditioning, heating, generators, water heaters, dehumidifiers and fans — and shows the arithmetic instead of asking for your phone number.

Why this site exists

Almost every sizing tool in this category is a lead capture form for contractors: you enter your details and get a sales call rather than a number. The arithmetic is not complicated and there is no reason it should cost you your contact details.

Where the data comes from

The formulas are the standard industry rules of thumb: roughly 20 BTU per square foot for cooling adjusted by climate, ceiling height, occupancy and exposure; climate-banded BTU per square foot for heating; DOE-standard capacity bands for dehumidifiers; running watts plus the largest starting surge for generators; first hour rating for water heaters. They are estimates and every page says so — a Manual J load calculation is the real answer and routinely differs by a size step. Electrical conductor sizing is deliberately not covered, because those figures come from code tables and getting them wrong causes fires.

Corrections

If you find a value that is wrong, please say so — corrections from readers are the fastest way this site improves. Email hello@whatsizehvac.com with the page and the value you measured, and it will be checked against the source.

Who runs it

A small independent project, funded by the advertising on the page. It is not affiliated with any manufacturer or contractor, and it does not sell or pass on leads because it does not collect anything to pass on.