About
About HVACCalc
HVACCalc is a free set of heating, ventilation and air conditioning calculators. It is the web companion to HVAC Calculator: BTU & AC Load, an iOS app, and runs the same formulas so a figure from the site matches the one on your phone.
Who makes it
The site and the app are published by Coffee Room SIA, a company registered in Latvia (registration no. 40103835510), Marijas iela 1-17, Rīga, LV-1050. The app is developed by Vyacheslav Dovner.
How the numbers are calculated
Every calculator states its method on its own page. In short:
- Room cooling load
- Room volume multiplied by 500 BTU/h per cubic metre for a shaded room or 600 for a sun-exposed one. This is the formula in the iOS app, so the site and the app return the same figure. For small US rooms the BTU calculator also shows the ENERGY STAR sizing chart by floor area.
- Unit conversions
- One ton of refrigeration is 12,000 BTU/h, one ton is taken as 3.52 kW, and one HP as 8,000 BTU/h — the constants used in the app.
- Whole-home load
- Room by room with the same volume formula, plus 600 BTU/h for each occupant beyond the first and 4,000 BTU/h for a kitchen.
- Exhaust fan airflow
- Room volume times the recommended air changes per hour for the room type, converted to CFM and m³/h.
- Duct sizing
- Equal-friction method for galvanized duct: the Altshul–Wright friction correlation from ASHRAE Fundamentals, and the Huebscher equation for the round equivalent of a rectangular duct.
Where a local rule of thumb differs from these formulas — watts per square metre in Germany, BTU per square metre in Brazil or Thailand — the page for that market shows both side by side rather than hiding the difference.
Where the estimates stop
These are sizing estimates for a first answer, not an engineering design. They do not model insulation, glazing orientation, climate data or infiltration the way a full load calculation does. For a new installation, have the system sized by a qualified professional using ACCA Manual J, S and D in North America, or EN 12831 and VDI 2078 in Europe.
Advertising and data
The website carries no ads and asks for no sign-up. The free version of the app shows ads, which a one-time Pro purchase removes. How the site and the app handle data is set out in the privacy policy; help with the app is on the support page.