Attic Fan Motor Replacement: Where to Buy, Costs & DIY

When an attic fan motor starts humming, squealing, or refusing to spin, the whole house feels it: heat builds overhead, your AC strains, and utility bills creep up. Maybe your vent used to pull hot air out effortlessly and now it barely moves air—or trips the breaker. The good news is that most attic fans are simple machines, and when they fail, the motor is often the culprit you can fix without replacing the entire unit.

A motor swap is usually straightforward and far cheaper than a full fan replacement—provided you buy the right motor and wire it correctly. Before you order anything, you’ll confirm the motor is actually bad (not the thermostat, fuse, or capacitor), gather the key specs from the old unit, and decide whether DIY or a pro makes more sense for your situation. With the right prep, many homeowners can complete the job in about an hour.

This guide shows you exactly how to do it: how to diagnose the issue, read your motor nameplate, and find compatible replacements online, locally, or from the manufacturer. You’ll see typical costs (parts and labor), tools and safety musts, step-by-step removal and wiring for gable and roof-mount fans, rotation and airflow testing, post-replacement troubleshooting, when upgrading the whole vent makes more sense, and maintenance tips to extend motor life.

Step 1. Check that the motor is the problem (not the thermostat, fuse, or capacitor)

Before you order a new motor, confirm it’s actually the culprit. Thermostats, fuses, capacitors, and even a tripped breaker can mimic a bad motor. Noises like grinding, squealing, or rattling, a hot electrical smell, or a fan that only starts when you spin the blade by hand are classic warning signs—but verify with a few fast checks first. Always turn power off at the breaker and use a non-contact tester to confirm.

• Set/override the thermostat: Turn the dial well below current attic temperature until it clicks. If nothing happens, temporarily bypass the thermostat (jumper its leads) to see if the motor runs. If it runs, the thermostat is bad.
• Check power and protection: Verify the breaker isn’t tripped. Inspect for an inline fuse or thermal fuse/thermal protector; if open, replace and clear dust around the motor vents to prevent repeat overheating.
• Inspect/diagnose the capacitor (PSC motors): A swollen or leaking run capacitor points to a cheap fix—replace it. If the blade spins freely but the motor only hums, suspect the capacitor.
• Spin and feel the blade: Rough, tight, or wobbly rotation suggests seized bearings—replace the motor. Free spin with hum favors a capacitor issue.
• Confirm voltage at the motor leads: If rated voltage (as on the nameplate) is present and the motor won’t run—or overheats quickly—the motor has likely failed.

If any step feels unsafe, stop and call a pro.

Step 2. Gather the right specs from your old motor (so you buy the correct replacement)

The fastest way to waste time and money is ordering a motor that “almost” fits. Before you shop, pull the old motor’s nameplate info and measure the physical details. Snap clear photos of the label, mounting, and shaft from multiple angles. If your vent has a model tag on the shroud, capture that too—many vendors cross‑reference by vent model for easy attic fan motor replacement.

• Voltage and phase: Must match exactly (commonly 120V single-phase; some are 240V).
• Horsepower and amps: Match HP; amperage should be similar to the original.
• RPM/speed: Match the rated RPM to keep airflow and noise where they should be.
• Rotation direction: Look for CW/CCW and notes like CWSE/CCWSE (clockwise/counter‑clockwise viewed from shaft end). If “reversible,” note the wire change method.
• Capacitor rating (PSC motors): Record microfarads (µF) and voltage. Replace with the same µF and equal or higher voltage.
• Mounting style and size: Belly band/strap, studs, or yoke; motor diameter and bolt pattern.
• Shaft details: Diameter, usable length, and end style (flat/D-shaft, smooth, threaded). Confirm the fan blade hub matches.
• Enclosure/ratings: Open air-over/ODP, thermal protection, ambient/temp rating as listed.
• Vent brand/model compatibility: Note tags like Master Flow EGV5/ERV4/ERV5 or PR/PG series; similar applies for Lomanco, Broan-NuTone, Air Vent, etc.
• Leads and connectors: Lead length, plug vs. bare leads, and any quick‑connects you’ll need.

Pro tip: If the label is unreadable, bring the motor (or detailed photos with measurements) to a motor shop or contact a seller with your vent’s model for a reliable cross-match.

Step 3. Where to buy an attic fan replacement motor (online, local, and manufacturer options)

With your specs and photos in hand, you’ve got three reliable paths: online motor specialists, big-box/home centers, and manufacturer or local parts channels. The goal is a drop‑in match—same voltage, HP, RPM, rotation, shaft, and mounting—so you’re not fighting the mounting ring or fan blade hub on install day.

• Online motor specialists: Retailers focused on motors list clear specs and brand compatibility. For example, some stock attic fan motors that cross to Dayton, Broan‑NuTone, Lomanco, and others, and many offer help matching by vent model.
• Marketplaces: Amazon carries universal‑fit PSC motors with different rotations, shaft lengths, and mounting styles. Use your nameplate to filter precisely—universal only works if the specs match.
• Big‑box/home centers: Home Depot sells OEM replacements like Master Flow’s PVM105 for EGV5/ERV4/ERV5 and PR/PG series, often noted as upgraded PSC motors that install without removing the vent. Menards carries Air Vent replacement motors.
• Manufacturer parts channel: If you know the exact vent series (e.g., PR3/PG3), ordering the brand‑specified motor via their authorized retailers ensures fit and wiring color codes line up.
• Local electric motor/HVAC supply shops: Bring the old motor and capacitor; they can match HP, RPM, frame/mount, and shaft, and provide the correct µF capacitor on the spot.

Before checkout, double‑confirm rotation notation (CW/CCW, “shaft end”), shaft diameter/length, mounting style, capacitor µF/voltage, and the seller’s return policy and lead time.

Step 4. Attic fan motor replacement costs (parts, labor, and when to call a pro)

Attic fan motor replacement costs hinge on two buckets—parts and labor—plus any access/safety fees. Expect the total to reflect your motor’s specs (HP, RPM, rotation), whether you choose OEM or a universal match, and how easy the vent is to reach. A simple way to frame it is: total cost = parts + (labor hours × hourly rate) + trip/roof fee + tax.

• Parts cost drivers: OEM vs. universal motor, included capacitor (or buying one separately), matching shaft and mount (to avoid buying a new blade/hub), new thermostat/humidistat if yours failed, and shipping/returns.
• Labor/time drivers: Roof‑mount vs. gable access, attic clearance/temperature, corrosion or seized blade hubs, and wiring condition. Some OEM options (e.g., upgraded PSC replacements designed to install without removing the vent) can cut labor time.

Call a pro if:

• Electrical risks exist: 240V circuits, aluminum wiring, damaged conductors, or repeated breaker trips/overheating.
• Roof hazards apply: Brittle shingles, steep pitch, or weather exposure.
• Compatibility is unclear: Unreadable nameplate, unknown rotation/wire changes, or mismatched blade hub.

Tip: Send photos of your nameplate, mount, and blade hub to the seller or contractor up front to get a firm parts match and a capped labor estimate.

Step 5. Prep for DIY: tools, safety, and timing

A smooth attic fan motor replacement starts with calm, cool conditions and good prep. Shut power off at the breaker and verify with a non-contact tester. Choose a cool morning, lay down plywood for stable footing, and set a parts tray nearby. Snap photos of the wiring and nameplate before you loosen anything—those shots save time when you reassemble.

• Tools and materials: Replacement motor, matching run capacitor (µF/voltage), screwdrivers and nut drivers, socket or wrench set, hex/Allen keys for the blade hub, penetrating oil, wire strippers/crimper, quality wirenuts or matching terminals, non-contact tester, multimeter, zip ties, marker/tape for labeling, and a small puller if the blade is stuck.
• Safety musts: Cut power at the breaker and tag it, wear gloves and eye protection, use a dust mask/respirator in insulation-heavy attics, headlamp and knee pads for comfort, and a stable ladder or roof fall protection for roof-mount units. When in doubt, get a helper.
• Timing tips: Work early (cool attic), pre-soak the blade hub set screw with penetrating oil, pre-bypass the thermostat for testing, and stage spare wirenuts and screws so you’re not hunting parts mid-project.

Step 6. Remove the old motor and fan blade (gable and roof-mount vents)

The goal is to get the motor out without bending the blade or losing the hub spacing that keeps airflow efficient. Work methodically: photograph wiring and mounting, label every lead, and mark how deep the blade sits on the shaft. If the hub is seized, don’t force it—remove the motor first and free the blade on a bench.

Gable-mount vents

Gable units are usually the easiest: you can often pull the motor and blade straight out from the attic. Some OEM replacements are designed to install without removing the housing; still, follow these basics.

• Kill power and document: Verify power is off, photograph wiring, and label leads.
• Remove guard/shroud: Unscrew the grille to access the blade and hub.
• Mark blade depth/rotation: Scribe the hub-to-shaft position and note rotation sticker.
• Loosen the blade hub: Back out the set screw (Allen). Add penetrating oil; use a small puller if needed. Don’t pry on blade tips.
• Free the motor: Undo the belly band/strap or stud nuts. Keep spacers and washers in order.
• Choose removal path:
  • If the blade comes off, lift the motor alone.
  • If the hub is stuck, remove motor with blade attached and separate on a workbench.
• Remove capacitor/bracket: If replacing, pull the old capacitor with its bracket.

Roof-mount power vents

Roof-mounts add ladder and weather risk. Many models let you swap the motor under the dome without removing the vent from the roof.

• Access and open the dome: Remove cap screws, lift the cover, and take off the guard.
• Label and disconnect wiring: Photograph, tag, and disconnect motor and capacitor leads.
• Mark the hub position: Note hub depth and rotation before loosening.
• Pull the blade: Loosen the set screw; wiggle from the hub. Use oil/puller if stubborn.
• Unbolt the motor: Remove bracket bolts/studs, preserving spacer order for blade clearance.
• Lift out the motor: Control small hardware so nothing rolls off the roof.

Step 7. Wire the new motor, capacitor, and thermostat correctly

Safe, correct wiring is the heart of a clean attic fan motor replacement. Follow the motor’s nameplate diagram—not color guesses. Most attic fan motors are PSC and require a matching run capacitor; use the same microfarads (µF) and equal or higher voltage. The thermostat/humidistat typically sits in series on the hot feed to control the motor; neutral returns directly to the motor per the diagram. Restore any temporary bypass you used for diagnosis and verify power is off before touching wires.

1. Mount the new capacitor securely, away from the blade path, using a metal bracket.
2. Route the supply hot to the thermostat/humidistat “LINE,” then from its “LOAD” to the motor lead indicated as line/hot. Keep neutrals together per the diagram.
3. Connect the motor’s capacitor lead(s) to the capacitor terminal(s) exactly as labeled (no polarity on run capacitors). Match the µF; don’t upsize.
4. Bond ground: green/bare to the motor frame and housing ground lug.
5. Make tight, code‑rated splices (wirenuts or terminals), tug test, and add strain relief/grommets through metal edges. Dress and zip‑tie wiring clear of the blade.
6. If the motor is reversible by lead swap, leave those two leads accessible for the next step. Briefly “bump test” without the blade only if the diagram is confirmed and you can do so safely.

Kill power again before reinstalling the blade.

Step 8. Set rotation, reinstall the blade, and test airflow

Correct rotation is what turns your attic fan motor replacement from “spins” into “moves air.” Confirm direction per the housing arrow or your notes (CW/CCW viewed from the shaft end). If the motor is reversible, set rotation per the wiring diagram and do a brief bump test without the blade to verify direction. Cut power again before installing the blade.

• Reinstall the blade: Align the hub set screw with the shaft flat, slide to your marked depth, and snug the set screw. Avoid pushing the hub so far that the blade hits the guard.
• Secure and dress wiring: Tie leads clear of the blade path; reattach guards/shrouds.
• Final tighten: Re‑check the hub set screw and motor mount hardware.
• Run test: Restore power and call for fan (thermostat set low or temporarily bypassed).
• Verify airflow direction: You should feel strong exhaust out of the vent and intake through attic inlets; a tissue should pull toward the intake, not blow away.
• Check for issues: No rubbing, minimal vibration, smooth ramp to speed, and no hot electrical smell.

If airflow is wrong, kill power and reverse the designated leads; if the motor isn’t reversible, you’ve got the wrong rotation model.

Step 9. Dial in thermostat/humidistat settings and do a safety check

With the new motor humming, set the controls so the fan runs when you need it—and shuts off when you don’t. Use a trusted thermometer/hygrometer at the thermostat location to avoid chasing bad readings, then run a quick safety walk‑down to lock in reliability.

Set your controls

• Stabilize readings: Place a thermometer by the thermostat for a few minutes to confirm actual attic temperature.
• Thermostat setpoint: Start with a practical on‑temperature that turns the fan on before heat builds (many homeowners begin near the low 100s °F and fine‑tune ±5°F for comfort/energy).
• Humidistat (if equipped): Start around a moderate RH (commonly ~60%) in damp seasons, then adjust to prevent condensation without over‑cycling.
• Verify cycling: Let the fan run, then confirm it shuts off as attic temp/RH drop.

Do a safety check

• Guards and cover: All shrouds/screens reinstalled; no rubs.
• Wiring and ground: Tight splices, strain reliefs/grommets in place, ground bonded.
• Capacitor mount: Bracketed securely, leads clear of the blade.
• Blade and mount: Hub set screw tight on the flat; no wobble or contact.
• Amp draw: After 5–10 minutes, motor amps at or under nameplate.
• Airflow and makeup air: Strong exhaust at the vent; soffit/inlet vents unobstructed; no drafts pulled from living space.
• Thermal comfort check: No hot electrical smell; breaker stays steady; thermostat cycles cleanly.

Step 10. Troubleshooting after replacement (noise, vibration, wrong rotation, overheating)

If your new attic fan motor runs but something feels off, work through the most common post-replacement issues methodically. Cut power before adjustments, and keep your nameplate specs handy so you can compare rotation, amperage, and capacitor values as you go.

• Scraping or rubbing sounds: The blade is too deep on the shaft or not centered. Slide the hub back to your mark, ensure the set screw sits on the shaft flat, tighten evenly, and confirm guard/shroud clearance.
• Vibration or wobble: Check that the blade isn’t bent; replace if warped. Tighten the motor strap/belly band and all bracket hardware. Preserve original spacers/washers. Clean debris from blades; imbalance amplifies shake.
• Wrong rotation/weak airflow: Verify direction against the housing arrow. For reversible motors, swap the designated leads per the diagram. Non‑reversible models require the correct rotation version. Recheck blade pitch (not flipped) and hub depth.
• Hums, slow start, or won’t reach speed: Match the run capacitor’s µF and voltage to the motor label; replace if swollen or mismatched. Confirm supply voltage at the motor and solid splices. A dragging blade or seized hub collar can also stall a good motor.
• Overheating or tripping after minutes: Measure amp draw with a clamp meter; it must not exceed nameplate amps. If high, suspect wrong µF capacitor, blade too deep creating overload, blocked ventilation around the motor, or tight bearings. Clear insulation from vents and ensure “air‑over” cooling.
• Thermostat chatter/rapid cycling: Move the sensor away from the exhaust stream, tighten connections, and widen the setpoint slightly. Verify neutral/hot routing matches the wiring diagram.

If problems persist, bench‑test the motor without the blade to isolate mechanical vs. electrical causes—or call a licensed pro, especially if amperage stays high or breakers trip repeatedly.

Step 11. When a full attic fan replacement or upgrade makes more sense

Sometimes a motor swap is only half the story. If the housing, blade, or controls are tired—or the fan is undersized for your attic—replacing the entire unit can deliver better airflow, lower noise, and longer life in one go. Modern attic fans and upgraded PSC designs run quieter and can add smarter controls, which may save you time and callbacks.

• Severe corrosion or UV damage: Rusted brackets, cracked dome/shroud, or broken guards.
• Bent blade or worn hub: Persistent wobble or imbalance even after careful re‑mounting.
• Undersized fan/poor airflow: Attic still bakes despite long run times; need higher CFM.
• Obsolete/unknown specs: Illegible nameplate, hard‑to-find rotation/shaft, or mismatched capacitor.
• Electrical damage: Scorched wiring, brittle insulation, or failing thermostat/humidistat.
• Noise goals: You want quieter operation (newer PSC units and isolation mounts help).
• Control upgrades: Desire integrated thermostat/humidistat or app/timer features.

If two or more apply, a full replacement may be faster, safer, and cost‑competitive. Match roof vs. gable style, confirm opening/flashing, and ensure you have enough intake vent area to support the new fan’s airflow.

Step 12. Maintenance tips to extend motor life

A little seasonal attention keeps your new motor cool, quiet, and efficient. After an attic fan motor replacement, think airflow first—motors rely on clean “air‑over” cooling—then confirm hardware and controls haven’t drifted. These quick checks prevent the dust, heat, and vibration that shorten motor life.

• Keep airways clear: Brush/vacuum dust from the guard and housing; pull insulation back from the motor vents and ensure soffit/intake vents aren’t blocked.
• Tighten hardware: Snug the blade hub set screw on the shaft flat and recheck motor mount/belly band bolts to curb vibration.
• Inspect the capacitor: Replace if swollen, leaking, or out of spec; match µF and equal/higher voltage.
• Verify controls: Test thermostat/humidistat cycling and confirm practical setpoints; avoid constant short cycling.
• Check wiring: Look for brittle insulation, loose wirenuts, chafed leads, and secure the ground.
• Listen and measure: Note new noises; if you own a clamp meter, confirm amps at or under nameplate after a 5–10 minute run.
• Skip random oiling: Most attic fan PSC motors use sealed bearings; only oil if the nameplate shows oil ports and specifies lubricant.

Final thoughts

If your attic fan has lost its punch, a smart motor replacement can bring back strong airflow, reduce attic temps, and ease the load on your AC—often in under an hour. You now know how to confirm the fault, pull the right specs, source a compatible motor, wire and set rotation correctly, and dial in the controls for safe, efficient operation. If the fan is corroded, undersized, or you’re chasing noise and reliability, a complete upgrade may serve you better than another patch.

Ready to solve heat build-up for good—or explore quieter, smarter ventilation beyond a motor swap? Talk with the team at Whole House Fan for expert guidance on attic, garage, and whole‑home solutions that fit your space, budget, and comfort goals.