Bathroom Guide
Bathroom Exhaust Fan With Heater: Sizing, Wiring and Cost
By Dioclecio Gomes, Founder & Owner4 min readUpdated October 8, 2026
A bathroom exhaust fan with heater pulls moisture out and warms the room from the ceiling. The Home Ventilating Institute sizes the fan at 1 CFM per square foot for bathrooms up to 100 square feet, or 50 CFM per toilet, shower and tub in larger rooms. Heater models draw real power: Panasonic's WhisperWarm uses a 1,600 watt heater and requires a minimum 20 amp dedicated circuit. Fixr puts a new installation at about $400 on average.
A bathroom fan with heater solves two problems at once: steam that lingers and a cold floor-to-ceiling chill on winter mornings. Sizing comes from the Home Ventilating Institute, wiring from the Panasonic product specs, venting from the International Code Council and pricing from Fixr. Planning a full remodel? See our bathroom remodeling page.
Why Does a Bathroom Need an Exhaust Fan?
Moisture. The EPA says the key to mold control is moisture control, and recommends running fans or opening windows to cut recurring bathroom mold. This Old House lists the warning signs of poor ventilation: mirrors that stay foggy long after a shower, mold or mildew in corners and on ceilings, peeling paint, water stains and musty odors. As contractor Tom Silva puts it there, a bathroom without a ventilating fan is like a fireplace without a chimney.
How Many CFM Does a Bathroom Fan Need?
The Home Ventilating Institute gives two methods.
| Bathroom | HVI recommendation |
|---|---|
| Up to 100 sq ft | 1 CFM per square foot (about eight air changes per hour) |
| Over 100 sq ft, per toilet | 50 CFM |
| Over 100 sq ft, per shower | 50 CFM |
| Over 100 sq ft, per tub | 50 CFM |
| Over 100 sq ft, per jetted tub | 100 CFM |
So an 8 by 5 foot bathroom needs at least a 40 CFM fan. A large primary bath with a tub, a separate shower and an enclosed toilet needs 150 CFM, often split between more than one exhaust point.
What Wiring Does a Fan With Heater Need?
More than a plain fan. Panasonic's WhisperWarm, for example, pairs selectable 50, 80 or 110 CFM airflow with a 1,600 watt self-limiting heater, and its spec sheet says a minimum 20 amp dedicated circuit is required. It also notes the heater performs best with ceilings no higher than 8 feet, and uses adjustable louvers to aim the heat. Check the installation guide for your exact model, and have a licensed electrician run the circuit. If the bathroom has no spare circuit, that wiring is part of the job.
Remodeling your bathroom?
We plan the fan, heater, duct and wiring with the rest of the remodel, and give you a written price after a free in-home visit.
Get a Free Bathroom EstimateWhere Should the Fan Vent, and How Long Should It Run?
Outdoors, never into the attic. The ICC study companion for the 2018 International Residential Code explains that when mechanical ventilation is used for bathrooms, the code sets minimum rates for continuous or intermittent fans, and in both cases the air must be exhausted directly to the exterior of the dwelling.
Placement and run time matter as much as size. HVI says exhaust points should sit over or near the shower or tub and in an enclosed toilet room, and recommends leaving the fan on for 20 minutes after using the bathroom, with a timer as a good solution. This Old House also suggests humidity sensors and multiple speeds.
How Much Does a Bathroom Fan With Heater Cost?
| Item (Fixr) | Typical cost |
|---|---|
| Fan with heater, unit only | $100 to $300 |
| Replacing an existing fan, installed | About $200 ($150 to $500) |
| New installation where there was no fan | About $400 ($250 to $900) |
| Labor | About $150 for a replacement, $300 for a first install |
Fixr says the biggest cost factor is whether you are replacing a fan or adding one where none exists, since a new install means running a duct to the outside through finished ceilings. The cheapest moment is during a bathroom remodel, when the ceiling is already open for the duct and the new circuit.
The Bottom Line
Size the fan by square footage or fixtures, vent it outdoors, and give the heater its own 20 amp circuit. If you are remodeling, add it while the ceiling is open. Get a Free Bathroom Estimate
FAQ
Does a bathroom fan with a heater need a dedicated circuit?
Usually yes. Panasonic's WhisperWarm, with a 1,600 watt heater, requires a minimum 20 amp dedicated circuit. Check the installation guide for your model.
How many CFM do I need for my bathroom fan?
The Home Ventilating Institute recommends 1 CFM per square foot for bathrooms up to 100 square feet, and 50 CFM each for a toilet, shower and tub (100 for a jetted tub) in larger bathrooms.
Can a bathroom fan vent into the attic?
No. The ICC study companion for the 2018 IRC explains that bathroom exhaust must be exhausted directly to the exterior of the dwelling.
How long should I run the bathroom fan after a shower?
The Home Ventilating Institute recommends 20 minutes after using the bathroom, and suggests a timer.
How much does it cost to install a bathroom fan with heater?
Fixr puts the unit at $100 to $300, a replacement install at about $200 and a new installation at about $400 on average, plus any new wiring the heater needs.
Sources:
Home Ventilating Institute, "Bathroom Ventilation"
Panasonic, "WhisperWarm DC Fan with Heater" product page
International Code Council, "2018 IRC Study Companion: Sections R303 through R310"
U.S. EPA, "A Brief Guide to Mold, Moisture and Your Home"
This Old House, "Bathroom Ventilation Problems Easily Solved"
Fixr, "How Much Does It Cost to Install a Bathroom Exhaust Fan?"