Free HVAC, Plumbing & MEP Engineering Calculators
A growing library of practical mechanical-engineering calculators for the repetitive checks designers perform every day — free, browser-based and no account required.
Exhaust & Ventilation Calculators
Calculate outdoor air, exhaust CFM, commercial kitchen hood airflow, makeup air and room air changes.
Duct Design Calculators
Move from fan pressure budget to friction rate, duct size, actual air velocity and diffuser or grille face area.
Hydronic Calculators
Convert load to GPM, calculate critical-circuit pump head, size buffer tanks and estimate water-system expansion tank volume.
Plumbing Calculators
Tally Canadian WSFU, size NPC 2020 sanitary drainage, check pipe velocity, calculate DHW recirculation flow and estimate water-heater recovery.
HVAC Equipment Sizing Calculators
Translate design loads into preliminary packaged rooftop-unit tons, airflow and heating-capacity targets.
From free calculator to complete project
Move the result into a connected MEP design workflow
The calculator library is built to capture quick engineering tasks. When the check becomes a complete project, move into MEPFlow for room loads, duct layout and sizing, plumbing pipe sizing and hydronic design.
Working with Canadian water-supply fixture units? Read the NPC 2020 domestic water pipe sizing guide.
Why MEPFlow Publishes Free Engineering Calculators
Mechanical design contains dozens of small calculations that engineers repeatedly rebuild in spreadsheets, search in handbooks or check with standalone tools. MEPFlow turns those high-frequency tasks into transparent browser calculators with the formula, assumptions and limitations shown alongside the result.
The calculators are intentionally useful on their own. They also connect logically: exhaust airflow leads to makeup air, available static leads to friction rate and duct sizing, hydronic load leads to GPM and pump head, and plumbing demand leads to pipe-velocity and recirculation checks.
Engineering Transparency, Not Black-Box Answers
Every calculator explains its calculation basis and flags where code editions, manufacturer data or fluid properties can change the final answer. That makes the library useful both for quick preliminary design and for independent checks of a separate design workflow.
Final construction documents still require the applicable codes and standards, complete system calculations, equipment performance data and professional engineering judgment. The goal is to eliminate repetitive arithmetic without hiding the assumptions that matter.