Makeup Air Calculator
Makeup air a big range hood or exhaust fan demands before it depressurizes the house.
Backdrafting a water heater or fireplace is the real hazard โ a 900 CFM hood in a tight house WILL pull flue gases backwards without MUA.
Formula
Makeup Air Calculator is a free makeup air for HVAC designers, technicians and energy auditors โ instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.
About Makeup Air Calculator
Makeup air a big range hood or exhaust fan demands before it depressurizes the house. The calculation implements MUA = ฮฃ exhaust โ infiltration credit (IRC trigger: hoods > 400 CFM) (IRC M1503.6 โ makeup air for range hoods). Backdrafting a water heater or fireplace is the real hazard โ a 900 CFM hood in a tight house WILL pull flue gases backwards without MUA.
How to use Makeup Air Calculator
- 1Enter Largest exhaust device in L/s.
- 2Enter Other simultaneous exhaust in L/s.
- 3Enter House leakage credit in L/s (Tight new homes: very little).
- 4Read Makeup air required instantly โ no submit button needed.
- 5Need US units? Flip the SI/Imperial toggle and every field converts.
Why use Makeup Air Calculator?
- โImplements the standard formula โ MUA = ฮฃ exhaust โ infiltration credit (IRC trigger: hoods > 400 CFM)
- โReference cited on-page: IRC M1503.6 โ makeup air for range hoods
- โOne-click SI โ Imperial toggle โ values convert in place, physics stays in SI
- โRuns entirely in your browser โ nothing uploaded, free forever
Frequently asked questions
What formula does the Makeup Air Calculator use?+
It computes MUA = ฮฃ exhaust โ infiltration credit (IRC trigger: hoods > 400 CFM), per IRC M1503.6 โ makeup air for range hoods. The formula is displayed under the result.
What should I keep in mind when using this calculator?+
Backdrafting a water heater or fireplace is the real hazard โ a 900 CFM hood in a tight house WILL pull flue gases backwards without MUA.
Is this based on ASHRAE methods?+
The calculations follow the standard ASHRAE/ISHRAE formulations cited under the result, simplified where industry practice does the same. For permit-grade design, confirm with the full code procedure.
Is the Makeup Air Calculator free to use?+
Yes โ completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.
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