HRV & ERV Calculator — CFM Sizing (ASHRAE 62.2)
Estimate the required whole-house ventilation rate (CFM) for an HRV or ERV using the ASHRAE 62.2 ventilation rate procedure. Includes optional blower-door infiltration credit and intermittent runtime sizing. Most homes need between 50 and 150 CFM — enter your floor area and bedrooms below to get your number.
Planning-grade sizing. Confirm local code requirements and commissioning targets.
On this page: Calculator · HRV vs ERV · Methodology · FAQ
Related: BTU calculator (equipment sizing) · Air leakage load calculator (infiltration & envelope) · Mini split calculator (ductless sizing) · Energy cost (operating cost)
Quick overview
Most whole-house ventilation sizing starts with: Qtot = 0.03 × floor area + 7.5 × (bedrooms + 1) (CFM). Use this tool to convert that target into an HRV or ERV airflow and pick a common size tier. Already know your CFM? Browse HRV & ERV units on Amazon.
Balanced ventilation note: with HRVs/ERVs, the effective whole-house ventilation rate is roughly the balanced supply/exhaust airflow (e.g., 80 CFM supply and 80 CFM exhaust ≈ 80 CFM ventilation).
Shop HRV & ERV units
Once you know your required CFM, look for a unit rated at or above that airflow at your expected duct static pressure. A 10–25% margin above your calculated target helps cover filter resistance and duct losses.
HRV vs ERV: which one should you choose?
HRV (heat recovery ventilator) transfers heat between outgoing and incoming air. It is commonly used in colder climates where indoor air tends to be dry in winter.
ERV (energy recovery ventilator) transfers heat and also some moisture. It is often preferred in humid climates because it can reduce the moisture brought in with outdoor air.
Either way, the sizing target is the same: pick a unit that can deliver your required CFM at real duct static pressure.
Frequently asked questions
What is the ASHRAE 62.2 ventilation rate formula?
The common prescriptive form is Qtot = 0.03 × floor area (sq ft) + 7.5 × (bedrooms + 1), in CFM. This estimates the target whole-house ventilation rate. A 2,000 sq ft 3-bedroom home needs roughly 0.03×2,000 + 7.5×4 = 60 + 30 = 90 CFM before any infiltration credit. Use the calculator above for your exact inputs.
Do supply and exhaust CFM add together on an HRV or ERV?
No. For balanced ventilation (typical of HRVs and ERVs), the effective whole-house ventilation rate is approximately the balanced supply/exhaust rate — not the sum of the two. An 80 CFM supply and 80 CFM exhaust delivers ~80 CFM of fresh air, not 160 CFM.
Should I size an HRV or ERV bigger than the required CFM?
Usually yes. Choose a unit that can deliver the required airflow at real duct static pressure — not just at zero static pressure (the rated spec). A margin of 10–25% above the calculated target helps cover filter resistance, duct losses, and commissioning variation. Browse HRV & ERV units to compare rated airflow at different static pressures.
What is the difference between an HRV and an ERV?
An HRV (heat recovery ventilator) transfers heat between outgoing stale air and incoming fresh air, recovering energy without transferring moisture. An ERV (energy recovery ventilator) transfers both heat and some moisture. ERVs are often preferred in humid climates to limit moisture introduction; HRVs are common in cold climates where indoor air is already dry in winter and added moisture is unwanted.
Is infiltration credit always allowed?
No. Some jurisdictions allow an infiltration credit based on blower-door testing; others require the full mechanical ventilation rate with no credit applied. Use the optional infiltration credit panel in the calculator above as a planning estimate, and confirm with your local mechanical code before finalizing the design.
What is a good CFM target for a 2,000 sq ft home?
It depends on bedrooms. Using the ASHRAE 62.2 form, a 2,000 sq ft 3-bedroom home is 0.03×2000 + 7.5×(3+1) = 60 + 30 = 90 CFM (before any infiltration credit).
Does an HRV/ERV need to run 24/7?
Many systems are designed for continuous operation, but some codes allow intermittent operation. If you run intermittently, you typically need higher airflow during runtime to hit the same average ventilation.
Should I use infiltration credit?
Only if it is allowed where you live (and you have reliable blower-door data). Some jurisdictions require the full mechanical ventilation rate with no credit.
Will a bigger HRV/ERV always be better?
Not necessarily. Oversized ventilation can dry the home in winter (cold climates) or increase indoor humidity load in summer (humid climates) if not controlled. Size to your target airflow and verify with commissioning.
Can I use this for code compliance?
This is a planning tool. For permits, follow your local mechanical code and any required design/commissioning documentation.
What size HRV or ERV do I need?
Most homes need between 50 and 150 CFM. Use the ASHRAE 62.2 formula above — a 1,500 sq ft 3-bedroom home needs roughly 75 CFM; a 2,500 sq ft 4-bedroom home roughly 112 CFM. Add a 10–25% margin when choosing a unit to account for duct resistance and filter pressure drop.
Last reviewed: 2026-03-03