Ventilation FansIn-Line Single-Port
Fantech FGC 8 (40423) Ventilation Fan Manual
Setup, everyday use, maintenance and troubleshooting for the 390 CFM in-line ventilation fan, with verified specifications.
- Airflow390 CFM
- Efficacy4 CFM/W
- Duct size8 in. round
About the Fantech FGC 8 (40423)
The Fantech FGC 8 (40423) is a 390 CFM in-line ventilation fan certified under the ENERGY STAR program. It belongs to the FG 8 Series line.
It is rated to move 390 cubic feet of air per minute at a single speed. It connects to an 8 in. round duct.
Fan efficacy is 4 CFM per watt, which means the motor draws roughly 98 W at 390 CFM.
Specifications
| Brand | Fantech |
|---|---|
| Model number | FGC 8 (40423) |
| Model name / series | FG 8 Series |
| Fan type | In-Line Single-Port |
| Rated airflow | 390 CFM |
| Fan efficacy | 4.0 CFM/W |
| Number of speeds | 1 |
| Duct connection (round) | 8.0 in. |
| Integrated light | No |
| ENERGY STAR Most Efficient | No |
Safety information
- Turn off power at the circuit breaker before installing, wiring or cleaning the fan, and confirm it is off with a non-contact voltage tester.
- Install and wire the fan in accordance with the instructions and local electrical and building codes. If you are unsure, hire a licensed electrician or HVAC contractor.
- Always duct the fan to the outdoors. Never terminate exhaust in an attic, crawl space, soffit vent or wall cavity — trapped moisture and grease cause mold, rot and fire risk.
- Mount the in-line fan to solid framing in an accessible location so it can be inspected and serviced, and keep it away from insulation that could block the motor housing.
- Do not use the fan to exhaust explosive or flammable vapors.
Installation and first-time setup
- Plan the system
In-line fans mount in the duct run — usually in an attic or basement — away from living spaces, which keeps them quiet. This single-port model connects to one intake duct, which can be fed by one or more grilles.
- Mount the fan
Fasten the fan to framing with the supplied brackets, using vibration isolators if provided, and leave access for service.
- Connect the ducts
Attach 8 in. round duct to the inlet and outlet collars with clamps or foil tape, observing the airflow arrow on the housing. Use insulated duct through unconditioned spaces.
- Wire the controls
Connect power and the wall control, timer or humidity control specified by the manufacturer. Many in-line fans are used for continuous whole-house ventilation at a low setting.
- Test
Run the fan and confirm airflow at each intake grille and that the exterior damper opens.
Using your ventilation fan
Continuous and boost operation
In-line fans are often run continuously at a low setting for whole-house ventilation, with a boost to a higher setting from a timer or humidity control when bathrooms are in use.
Care and maintenance
| When | What to do |
|---|---|
| Every 3–6 months | Remove the grille (it usually unclips with spring wires), wash it in warm, soapy water and vacuum dust from the housing and fan blades with power off. |
| Every year | Check outdoors that the damper flap opens freely and the exterior cap is clear of lint, nests and debris. |
| Every few years | Inspect accessible duct runs for disconnected joints, crushed sections or condensation. |
Troubleshooting
Weak airflow and excess noise are almost always caused by the duct system rather than the fan. Turn off power at the breaker before removing the grille or touching the motor.
| Problem | Possible cause | What to try |
|---|---|---|
| Fan runs but moves little air | Damper stuck closed; duct crushed, disconnected or too long; dirty grille or filter. | Check the exterior damper and cap, inspect the duct, and clean the grille or filters. |
| Louder than expected | Restrictive or undersized duct; loose grille; housing not secured. | Use duct at least as large as the collar (8 in. round), tighten the grille and mounting screws. |
| Rattling or flapping sound | Backdraft damper fluttering in wind; loose duct. | Secure the duct and check that the damper closes fully; a wall cap with a better damper may help. |
| Water dripping from the grille | Condensation in an uninsulated duct; duct sloped back toward the fan. | Insulate the duct in unheated spaces and slope it toward the exterior. |
| Fan will not start | Breaker off; switch or timer failed; motor plug loose in the housing. | Check the breaker, test the switch, and with power off confirm the motor is plugged into its receptacle. |
| Cold drafts from the fan when off | Damper not closing; unsealed housing. | Free or replace the damper and seal around the housing. |
Energy use and running costs
Ventilation fan certification lists airflow and efficacy rather than annual energy use. From 390 CFM at 4 CFM/W, the Fantech FGC 8 (40423) draws roughly 98 W. The table estimates yearly use at an average electricity price of $0.17 per kWh.
| Scenario | Power | Energy per year | Cost per year |
|---|---|---|---|
| Boost, 2 h/day | 98 W | 71.2 kWh | $12.10 |
| Continuous at 390 CFM, 24 h/day | 98 W | 854 kWh | $145 |
The motor is only part of the cost: every cubic foot exhausted is replaced by outdoor air that must be heated or cooled. Run the fan as long as needed to clear moisture, then let a timer or humidity control switch it off — unless it is providing intended continuous ventilation.
Frequently asked questions
How many CFM is the Fantech FGC 8 (40423)?
It is rated at 390 CFM.
What size duct does the Fantech FGC 8 (40423) need?
It has an 8 in. round duct connection. Use duct at least that size all the way to the exterior cap; reducing it cuts airflow and raises noise.
How much electricity does the Fantech FGC 8 (40423) use?
With an efficacy of 4 CFM/W it draws roughly 98 W at 390 CFM. Running one hour a day costs about $6.05 a year at $0.17/kWh.
Does the Fantech FGC 8 (40423) have a light?
No. The certified configuration does not include a light.
Sources and disclaimer
Specifications on this page come from the ENERGY STAR certified ventilation fans dataset published by the U.S. Environmental Protection Agency (record certified June 5, 2025), retrieved October 7, 2026.
The setup, operating, maintenance and troubleshooting guidance is written by ManualHarbor's editors for this specific product type and configuration. It is an independent guide — not a reproduction of the manufacturer's manual — and ManualHarbor is not affiliated with Fantech. Always follow the safety instructions, installation requirements and warranty terms supplied with your unit, and contact Fantech or an authorized service provider for warranty repairs and replacement parts.
Running-cost figures use assumed U.S. average utility prices and are estimates for comparison only. See our editorial methodology for details.
Report a problem with this guide
Spotted a wrong value, a broken link or something unclear? Tell us and we will review it.