Why Can’t a Ridge Vent and a Roof-Mounted Attic Fan Work Together?

During a recent roof replacement in Ridgewood, a homeowner asked a common question: "If I already have a ridge vent, why isn't my new attic fan helping?" The answer revealed a ventilation problem hiding in plain sight—two exhaust systems fighting each other instead of working together.

Attic ventilation problems are rarely caused by a lack of vents. More often, they are caused by too many exhaust systems working against each other.

One of the most common ventilation mistakes seen during roof work is leaving a ridge vent open while installing a roof-mounted attic fan. While both components are designed to exhaust air, combining them incorrectly can prevent the attic from ventilating properly.

This article explains why ridge vents and roof-mounted attic fans conflict, what a ventilation “doom loop” is, and how the system should be corrected.

Quick Answer: Ridge vents and roof-mounted attic fans should not be used together because they create competing exhaust paths. The fan pulls air from the nearby ridge vent instead of from intake vents throughout the attic, creating a "doom loop" that prevents proper ventilation.

What Is a Ridge Vent and What Does It Do?

A ridge vent is a passive exhaust ventilation system installed along the peak of the roof. It relies on natural convection—hot air rising—to allow warm, moist air from the attic to escape through an opening at the ridge.

As described on-site, “This is a three inch gap at the apex of the roof.”

That opening is covered with a vent product designed to:

• Allow hot air to escape

• Prevent water intrusion

• Keep animals and debris out

When paired correctly with intake ventilation, ridge vents can be an effective exhaust method. [Learn more about proper attic ventilation systems →]

What Is a Roof-Mounted Attic Fan?

A roof-mounted attic fan is an active exhaust system. It uses a motor, controlled by a thermostat or humidistat, to mechanically pull air out of the attic when certain conditions are met.

When attic temperatures rise too high—or humidity becomes excessive—the fan activates and forces air out of the roof.

Unlike passive systems, attic fans create suction and actively move air.

Why Is It a Problem to Have Two Exhaust Systems?

Ventilation systems must be balanced. Every exhaust system needs a clear, unrestricted source of intake air.

The problem arises when two exhaust methods are installed too close together.

As explained during the installation, “This is an exhaust method or an exhaust mechanism of a roofing system.”

When both a ridge vent and a roof-mounted attic fan are left open, they compete instead of cooperating.

What Is the “Ventilation Doom Loop”?

A ventilation doom loop occurs when an exhaust fan pulls air from the closest available opening, rather than from the entire attic space. Think of it like a vacuum cleaner with a hole in the hose—instead of pulling air from the floor, it just pulls air through the hole. The motor runs, but the floor never gets clean.

If a ridge vent remains open near a roof-mounted attic fan:

• The fan pulls air directly from the ridge vent

• Air exits the fan

• The fan immediately pulls that same air back in

• Ventilation occurs only in a small localized area

The rest of the attic receives little to no airflow. This creates excessive air movement in one spot and stagnation everywhere else.

• Ridge vent at peak

• Attic fan nearby

• Arrows showing air short-cycling between the two

• Stagnant air in far corners of attic

• Label: "Air follows path of least resistance"]

How Can Homeowners Tell If They Have This Problem?

Several signs may indicate a ridge vent and attic fan are working against each other:

• The attic fan runs frequently but the attic remains hot

• Temperature varies dramatically between different areas of the attic

• Moisture or condensation appears in some sections but not others

• Energy bills remain high despite the attic fan operating

• The fan seems to run constantly without achieving the desired temperature

If any of these conditions exist, a ventilation evaluation can determine whether competing exhaust systems are the cause.

Why Doesn’t the Fan Pull Air From the Whole Attic?

Air follows the path of least resistance.

Instead of drawing air evenly from intake vents throughout the attic, the fan will pull from the nearest open exhaust opening, which is the ridge vent itself.

This prevents:

• Proper attic air exchange

• Consistent temperature regulation

• Moisture removal across the full attic

Despite the fan running, the attic is not truly ventilated.

How Is This Ventilation Problem Corrected?

To correct the conflict, one exhaust system must be eliminated.

In this scenario, the solution is to:

• Close off the ridge vent opening

• Allow the roof-mounted attic fan to become the sole exhaust system

This ensures the fan pulls air from intake vents throughout the attic rather than short-cycling nearby.

In Bergen County, building codes require balanced ventilation systems with proper intake-to-exhaust ratios. When correcting ventilation conflicts during roof replacements, Mattsson Roofing ensures all modifications meet current code requirements and manufacturer specifications for both roofing materials and ventilation products.

Why Is Ice and Water Shield Used to Close the Ridge Vent?

Ice and water shield is a waterproof, non-breathable membrane.

When installed over the ridge vent opening:

• It blocks airflow completely

• It prevents water intrusion

• It permanently deactivates the ridge vent

Once covered, ridge cap shingles are installed over the membrane to fully seal the area.

This ensures no air can escape at the ridge, forcing the attic fan to ventilate the entire attic as intended.

Why Must a Roof Have Only One Exhaust Strategy?

Attic ventilation works as a system, not a collection of parts.

A roof should have:

• Intake ventilation (soffits or lower vents)

• One clear exhaust strategy

Multiple exhaust points placed too close together undermine airflow patterns and reduce overall effectiveness.

This is why ventilation design must be intentional, not additive.

What Happens If This Issue Is Left Uncorrected?

If a ridge vent and attic fan are left open together:

• The attic may overheat despite the fan running

• Moisture may remain trapped in sections of the attic

• Energy efficiency suffers

• Shingle lifespan can be reduced

• Homeowners may believe ventilation is working when it is not

The system appears active but performs poorly.

Frequently Asked Questions About Ridge Vents and Attic Fans

Can a ridge vent and attic fan ever be used together? In most residential systems, no. Using both creates competing exhaust paths that reduce overall ventilation effectiveness. One exhaust strategy should be selected and designed properly.

Why does my attic fan run constantly but my attic still feels hot? This is often caused by short-cycling, where the fan pulls air from a nearby ridge vent instead of from intake vents throughout the attic. The fan is working, but the attic is not being ventilated properly.

Is closing a ridge vent a permanent solution? Yes, when a roof-mounted attic fan is chosen as the primary exhaust method. Closing the ridge vent ensures the fan functions correctly and ventilates the entire attic space.

Will closing my ridge vent void my shingle warranty? No, as long as the attic maintains proper ventilation through the roof-mounted fan and intake vents. Shingle manufacturers require adequate ventilation—not a specific exhaust method. Closing a ridge vent to eliminate ventilation conflicts actually improves overall system performance.

How much does it cost to correct this ventilation problem? When addressed during a roof replacement, closing a ridge vent adds minimal cost—typically just materials and labor for ice and water shield installation. Correcting the issue on an existing roof may involve additional work depending on the roof's age and condition. A ventilation evaluation can provide specific pricing.

Schedule Your Free Attic Ventilation Assessment Today

For homeowners in Bergen County and surrounding areas experiencing attic ventilation issues—or planning a roof replacement where ventilation needs to be addressed—Mattsson Roofing is here to help. Our comprehensive evaluations assess your entire roofing and ventilation system, identify conflicts like the doom loop described above, and provide clear solutions that work.

[Schedule Your Free Attic Ventilation Assessment Today] and discover whether your attic is truly ventilated—or just moving air in circles.

[If you've recently received a roof replacement notice from your insurance company →], our evaluations can address both roofing and ventilation concerns in one comprehensive assessment.