In short
- A barndominium exhaust fan calculator has two parts: a whole-house rate from floor area and bedrooms, and local minimums for the kitchen and each bathroom.
- Local minimums (IRC Table M1505.4.4): kitchen 100 cfm intermittent or 25 cfm continuous; bathroom 50 cfm intermittent or 20 cfm continuous.
- Bathroom fans are rated at 0.25 inch water column. Use the fan's rated number at that pressure, not the free-air figure on the box.
- The example, 2,400 sq ft with 4 bedrooms, gets a 75 cfm whole-house rate from the table.
On this page
This barndominium exhaust fan calculator is for Tyler and Smith County owners who want to know what airflow to ask the builder for in the kitchen, the bathrooms and the whole house. Enter the floor area, bedrooms and bathrooms, and it gives the minimum cfm the code table asks for. It pairs with our HVAC size calculator, since the air a fan removes is air the system has to replace.
En español: calculadora de ventiladores de extracción
| Item | Minimum | Your fan |
|---|
Example: 2,400 sq ft, 4 bedrooms, 3 bathrooms, local fans on demand (intermittent).
How the airflow is worked out
- Find the whole-house rate.
Look up floor area and bedroom count in Table M1505.4.3(1). Example: 2,400 sq ft falls in the 1,501 to 3,000 row; 4 bedrooms is the 4 to 5 column: 75 cfm.
- Check the code equation.
Equation 15-1: 0.01 x floor area + 7.5 x (bedrooms + 1). Example: 24 + 7.5 x 5 = 61.5 cfm. The code accepts either figure; we show both.
- Add the local minimums.
Kitchen: 100 cfm intermittent or 25 cfm continuous. Each bathroom: 50 cfm intermittent or 20 cfm continuous. Example: 3 bathrooms x 50 = 150 cfm of bath fans.
- Compare with the fans on the plans.
Use the rated cfm at 0.25 inch water column. A fan rated below the minimum is short even if it moves air.
Whole-house rate by floor area and bedrooms
| Floor area | 2-3 bed | 4-5 bed | 6-7 bed |
|---|---|---|---|
| 1,500 sq ft or less | 45 | 60 | 75 |
| 1,501 to 3,000 sq ft | 60 | 75 | 90 |
| 3,001 to 4,500 sq ft | 75 | 90 | 105 |
| 4,501 to 6,000 sq ft | 90 | 105 | 120 |
Continuous airflow in cfm, from Table M1505.4.3(1). Homes with 0 to 1 bedrooms or more than 7 are in the code table too; the calculator covers them.
Local exhaust minimums (Table M1505.4.4)
| Room | Intermittent | Continuous |
|---|---|---|
| Kitchen | 100 cfm | 25 cfm |
| Each bathroom or toilet room | 50 cfm | 20 cfm |
Bathroom fans must meet the rate at 0.25 inch water column static pressure.
Where fan sizing goes wrong
- Reading the box, not the data sheet. The big number is often free-air cfm. The code rate is at 0.25 inch water column.
- Long, bent ducts. A fan can move far less than its rating through a long run with elbows. Ask how long the duct is and where it ends.
- Recirculating hoods. A hood that filters and returns air to the room does not exhaust anything. Ask if the hood is ducted outdoors.
- Exhausting into the attic. The code asks for discharge to the outdoors (M1501.1). A fan that dumps humid air into a vented attic or a foamed roof cavity is a moisture problem. See the insulation and condensation guide.
- A big hood and a tight house. Above 400 cfm, makeup air may be required (M1503.6). Ask the designer who handled it. The attic ventilation calculator covers the roof side.
What to ask your builder
- Which fans are in the plans? Ask for make, model and rated cfm at 0.25 inch water column for each bath fan and the hood.
- Where does each duct end? Outdoors, with a wall or roof cap, not into the attic or soffit.
- Is there a whole-house ventilation system? If so, which fans or what unit supply it, and what controls.
- Does the building department agree? Ask which code edition applies. See permits in Smith County.
Next step: get a written quote
This tool sizes fan airflow, not the building or the price. We are a referral service, not a contractor; we connect visitors with independent local providers. Use the form below to ask independent barndominium builders near Tyler for a written quote that lists each fan and its rated cfm, and read how to choose a barndominium builder first.
Sources
- Chapter 15 Exhaust Systems, Texas-adopted 2021 International Residential Code: M1505.3 (fan rating), M1505.4.3 (Table M1505.4.3(1) and Equation 15-1), M1505.4.4 (Table M1505.4.4), M1503.6 (makeup air above 400 cfm).
Frequently asked questions
How many cfm does a barndominium kitchen exhaust fan need?
The International Residential Code (Table M1505.4.4) sets a minimum of 100 cfm for a kitchen fan that runs on demand, or 25 cfm if it runs continuously. Most range hoods are rated well above that, so the code minimum is rarely the limit. The limit is usually the duct length and bends, and the rating is only meaningful at the pressure the code names.
How many cfm does a bathroom exhaust fan need?
Table M1505.4.4 asks for 50 cfm intermittent or 20 cfm continuous for each bathroom or toilet room. The listed rate must be met at a static pressure of 0.25 inch water column, which is the rating to look for on the fan's label or data sheet, not the free-air number on the box.
What is whole-house mechanical ventilation, and does a barndominium need it?
M1505.4 describes a system that supplies or exhausts outdoor air continuously at a rate set by floor area and bedroom count (Table M1505.4.3(1)) or by Equation 15-1. Whether it is required depends on the home's air tightness and the code edition and local amendments your building department enforces, so ask which applies. This tool shows the rate the code gives so you can see what a system would need to deliver.
Can the bathroom and kitchen fans count as the whole-house system?
M1505.4.1 says local exhaust or supply fans are permitted to serve as the whole-house system. A fan used that way has to meet the whole-house rate and run on the schedule the code allows, with a manual override control. Ask the designer to say in writing which fans do double duty.
When does a big range hood need makeup air?
IRC M1503.6 asks for makeup air at about the same rate when an exhaust system can move more than 400 cfm and a fuel-burning appliance that is not direct-vent is inside the home's air barrier. A large hood over an electric range in a tight house is a separate design question. Ask your builder and mechanical designer to address it.
Which code applies in Tyler, Texas?
The text we checked is the Texas-adopted 2021 International Residential Code (chapter 15, Exhaust Systems). Cities and counties adopt editions and amendments on their own schedule, so ask the building department which edition applies to your permit. See our guide to barndominium permits in Smith County.
Does the calculator give a price?
No. It gives airflow numbers only, with no prices. Ask for written quotes that list each fan and its rated cfm at 0.25 inch water column.