Calculators

Ventilation calculators

A tight house needs ventilation designed in, not left to leaks. These calculators give the whole-dwelling mechanical rate, the local exhaust for baths and kitchens, and the air change numbers a blower door test or a room volume produces.

Each page names the standard or code section it works from. The range hood calculator also flags the 400 CFM threshold where makeup air comes into question.

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Which one you need

Every tool in this section

  • Ventilation

    ASHRAE 62.2 Ventilation Calculator

    Whole-dwelling mechanical ventilation rate from floor area and bedroom count.

    Applies Qtot = 0.03 x floor area + 7.5 x (bedrooms + 1). The page text explains the IRC M1505.4.3 formula with its smaller 0.01 coefficient, which the calculator does not compute.

    Based on ANSI/ASHRAE Standard 62.2

  • Local exhaust

    Bathroom Exhaust Fan Calculator

    Bath fan CFM by floor area or by fixture count, rounded up to a standard fan size.

    Scales the area method for ceilings above 8 ft and keeps the 50 CFM code minimum as its own check.

    Based on HVI guidance, IRC M1505.4.4

  • Ventilation

    Air Changes per Hour Calculator

    ACH from CFM and room volume, CFM for a target ACH, and ACH50 from a blower door test.

    Checks ACH50 against the IECC limit for the climate zone and edition you pick. The natural infiltration estimate is shown as a rough figure.

    Based on IECC 2021 and 2024 air leakage limits

  • Local exhaust

    Range Hood CFM Calculator

    Kitchen hood CFM by cooktop width and hood position, checked against the code minimum.

    Flags makeup air above 400 CFM when a fuel-burning appliance is inside the air barrier. The gas BTU rule of thumb is shown for reference only.

    Based on HVI guidance, IRC M1505.4.4 and M1503.6

Other calculators

Every calculator here lists the standard it works from and what it leaves out. The numbers are for sales-phase sizing and field checks, not a permit submittal. Methodology lists the standard behind each one.