Disclaimer

Supply & Return provides HVAC calculators and explanations for general information and education. Please read this page before relying on a result for a purchase, an installation or a permit.

Estimates, Not Designs

The calculators use simplified methods: area-based room sizing, steady-state conduction and leakage for heat loss, standard-air constants for airflow and the friction equation for smooth round duct. Real loads depend on orientation, shading, internal gains, humidity, duct location and many details the tools do not model. Equipment selection for a whole house should be based on a full load calculation such as ACCA Manual J, equipment selection to Manual S and duct design to Manual D, carried out by a qualified professional.

Safety-Critical Work

Gas appliances, flues, electrical connections and refrigerant circuits can cause fire, explosion, electric shock, carbon monoxide poisoning and environmental harm if installed or repaired incorrectly. That work must be done by appropriately licensed technicians and in line with local codes and the manufacturer's instructions. Nothing on this site tells you how to perform it. Combustion appliances need adequate combustion air and working carbon monoxide alarms; ventilation changes in a house with atmospherically vented appliances should be checked for back-drafting by a professional.

Codes and Standards Change

Efficiency minimums, ventilation requirements and test procedures change over time and differ between jurisdictions. We describe ASHRAE 62.2-2016, the 2023 SEER2 rules and ENERGY STAR guidance as we understand them, but your local building department decides what applies to your project.

Savings and Costs

Energy savings and payback figures depend on your cooling hours, energy prices, installation quality and how you use the system. Actual bills may differ substantially from the estimates.

Altitude and Climate

The 1.08 airflow factor and the 0.018 leakage factor assume sea-level air. At high altitude, air is thinner and carries less heat per cubic foot, so the same load needs more airflow.

Errors and Changes

We test the calculators carefully, but mistakes are possible. Please report any you find to logan.luo@adsnova.cn. To the extent permitted by law, we accept no liability for decisions, purchases or installations based on the site.