About this site

What the site is

HVACs Calculator has 61 calculators for the questions that come up when a house is heated, cooled or ventilated: what size air conditioner, furnace, heat pump or mini-split it needs; how big the ducts, registers and returns should be; how much fresh air and exhaust the code asks for; what a system costs to run and to install; and how big a water heater should be. They are written for homeowners comparing quotes, for DIYers sizing a room unit or a bathroom fan, and for contractors who want to show a customer the arithmetic.

Heating and cooling equipment is one of the largest purchases in a house, and the most common mistake, an oversized system, is invisible until the house feels clammy or the bills arrive. Most online tools give one number from one national rule of thumb. This site starts from the climate zone, shows each adjustment, rounds to sizes that are actually sold, and says which professional standard would confirm the answer.

How the calculators are built

Each calculator is a small program with an explicit formula, listed on its page under "How we calculate this". The same code produces the example result shown when the page loads, the result you get when you press Calculate, and the worked examples in the text, so the three can never disagree. Before a calculator is published it is run against a set of test cases with known answers, including unit conversions, and it is published only when they all pass.

The defaults come from public sources: the US Department of Energy and ENERGY STAR for climate zones, room air conditioner sizing, efficiency ratings and the water heater sizing worksheet; the Energy Information Administration for fuel energy content and average prices; ASHRAE for duct friction, ventilation (Standard 62.2) and equipment service lives; the International Residential Code and the Home Ventilating Institute for exhaust fans and range hoods; ACCA's Manual S limits for equipment sizing; and dated 2025 and 2026 cost guides for installed prices. Each calculator's assumption table says which figure was used and when it was last checked; the methodology page lists the sources in one place.

Who writes it

The site is written and maintained by its publisher, with AI writing tools used to draft and to check text, and with every number, formula and claim reviewed by a person before it goes up. We say this plainly because readers deserve to know how what they read was made. The editorial policy sets out the rules we follow, how corrections are handled, and how advertising is kept separate from content.

What the site does not do

• It does not ask you to sign up, and it keeps nothing you type into a calculator. The arithmetic runs in your browser.
• It does not take money from the companies whose products its calculators touch, and it does not recommend specific products.
• It does not claim precision it does not have. Where a figure is an estimate, the page says so and says how wide the uncertainty is.

Contact

Found a result that looks wrong, a source that has changed, or a calculator you wish existed? Use the contact form or write to contact@hvacscalculator.com. Reports of errors are checked first and answered.