Are roof exhaust fans worth it?

Roof exhaust fans, also known as roof ventilators, are a great way to improve ventilation and air quality in your home. But are they really worth investing in? Here we’ll examine the pros and cons of roof exhaust fans to help you decide if installing one is right for your home.

What are roof exhaust fans?

Roof exhaust fans are fans mounted on the roof that pull hot, stale air up and out of the attic. This creates negative pressure that draws fresh air in through open windows and doors. Exhaust fans are usually powered by an electric motor and have an enclosing hood to protect the fan from weather.

There are two main types of roof exhaust fans:

• Roof ventilators – Designed to ventilate attics and create airflow through passive ventilation. They run continuously to remove heat and moisture.
• Roof mount power attic ventilators – More powerful fans designed to actively push hot air out of attics. They have higher airflow capacities and can be controlled by thermostats.

What are the benefits of installing a roof exhaust fan?

Here are some of the top benefits that a roof exhaust fan can provide:

• Improves attic ventilation – Roof fans enhance attic ventilation by creating negative pressure. This draws fresh, outdoor air into the attic through soffit vents, lowering heat and humidity.
• Cools and dehumidifies home – By ventilating the hot attic, roof fans allow cooler outside air to enter the living space through windows. This can lower indoor temperatures by up to 10°F.
• Prevents issues caused by poor ventilation – Stale attic air can cause moisture buildup and high humidity. Adequate ventilation prevents condensation, mildew growth and wood rot.
• Lowers energy bills – Keeping attics cooler requires less air conditioning to cool living spaces. Roof fans can lower AC costs by up to 17% according to Department of Energy studies.
• Extends roof life – By removing heat from attics, exhaust fans prevent premature wear and aging of roof materials caused by excessive heat exposure.
• Improves indoor air quality – Stale, humid air can accumulate odors, mold, mildew and other allergens. Ventilation brings in fresh outdoor air, creating a healthier home.

What are the downsides of roof exhaust fans?

While roof exhaust fans have many benefits, there are also some potential drawbacks to consider:

• Upfront costs – Roof ventilators can cost $200 to $1,500 installed depending on type, size and features. Power attic ventilators cost $500 to $3,000+.
• Recurring energy costs – Fans require electricity to run, adding $3 to $15 per month depending on use. Models without thermostat controls run continuously.
• Roof leaks – Poor installation can result in water leaks. Fans must be properly flashed and sealed to prevent leaks.
• Noise – Powerful fans generate noise levels around 50 – 70 dBA. This may be audible in some living spaces.
• Draftiness – High airflow can create drafty interior spaces. Controls may be needed to moderate fan speed.
• Attic insulation disturbance – Improper installation can leave gaps in insulation, reducing its effectiveness.

How much do roof exhaust fans cost?

Roof exhaust fan costs vary considerably based on size, type, features and more. Here are typical price ranges:

Fan Type	Typical Cost Range*
Roof Ventilator	$200 – $1,500
Roof Mount Power Attic Ventilator	$500 – $3,000+

*Cost range includes professional installation

Fan size is the primary factor impacting cost. Standard residential units are usually between 16 inches and 36 inches in diameter. Larger fans above 50 inches cost over $2,000 installed.

Features like thermostats, humidistats, automatic dampers and roof curbs add to the total price. Higher CFM ratings, durable motors and metal construction increase costs as well.

How to determine the right size roof fan

Choosing the appropriate roof fan size is essential for proper attic ventilation. Undersized fans won’t move enough air, while oversized units are noisy and waste energy.

The general recommendation is to have 1 square foot of net free vent area for every 300 square feet of attic space. This is divided between intake vents (soffit vents) and exhaust vents (roof fans) in a 50/50 ratio.

For example, an attic measuring 30′ x 50′ = 1,500 square feet would need:

• Total Net Free Vent Area = 1,500 sq ft / 300 = 5 sq ft
• Intake Vent Area = 5 sq ft x 0.50 = 2.5 sq ft
• Exhaust Vent Area = 5 sq ft x 0.50 = 2.5 sq ft

When selecting exhaust fans, choose models rated for the desired cubic feet per minute (CFM) airflow. CFM ratings should match the calculated vent area for your attic size.

Where should roof exhaust fans be located?

Proper placement is key to maximize roof fan effectiveness. Guidelines for optimal location include:

• Near the highest point of the attic – Ensures hot air is removed from the highest areas.
• Near the center – Centrally located to create even airflow through entire attic.
• At least 3 feet from intake vents – Prevents short cycling of air from intake to exhaust.
• At least 5 feet from plumbing vents – Avoids moisture intake and corrosion.
• Not above bedrooms – Minimizes noise disruption.

Fans should be positioned to draw air along the entire underside of the roof sheathing, creating uniform ventilation.

How many roof exhaust fans are needed?

Most homes only need one or two roof exhaust fans to adequately ventilate the attic. The number required depends on:

• Attic size
• Amount of existing ventilation
• Climate conditions

Use the 1:300 rule to calculate total net free vent area needed. Divide by the exhaust vent area ratings of chosen fans to determine quantities needed.

One large, centrally located exhaust fan is typically sufficient. Larger or complex rooflines may benefit from two properly positioned units.

Do roof exhaust fans really work?

When sized and installed correctly, roof exhaust fans are highly effective at ventilating attics. Power attic ventilators actively remove massive amounts of hot air, creating significant cooling.

Studies by the U.S. Department of Energy found attics with power ventilators run 3-5°F cooler than those without. This is confirmed by field research showing temperature drops of up to 30°F after installing exhaust fans.

By pulling hot air out of attics, roof ventilators lower heat transfer into living spaces. This directly results in cooler indoor temperatures and lower air conditioning costs.

Roof fans also improve air quality by diluting odors, smoke, chemicals and other pollutants. Replacing stale indoor air can reduce dust mites, mold spores and other allergens as well.

Do roof fans increase energy efficiency?

Properly installed roof exhaust fans have been shown to directly increase home energy efficiency in two ways:

1. Lower attic temperatures – Less heat transfer means ACs run less to cool the home interior, reducing electricity usage.
2. Prevent issues causing energy loss – Removing moisture and heat improves insulation, weatherproofing, etc. to prevent energy leaks.

Studies by the Florida Solar Energy Center found homes with power roof ventilators used up to 17% less air conditioning than other homes. This resulted in cooling energy savings of up to $256 per year.

The DOE found that enhancing attic ventilation can lower cooling costs by 10-25% annually. Heating costs may decrease slightly thanks to insulation preserved by a drier attic.

Do roof exhaust fans reduce humidity?

Roof exhaust fans are highly effective at reducing attic and indoor humidity levels. By constantly pulling humid attic air outside, they prevent moisture buildup.

Attics act as moisture buffers for living spaces. If allowed to become humid, moisture can condense on wood, insulation and other surfaces. This leads to mold, mildew, rot and structural issues.

Ventilating attics to the exterior minimizes humidity-related problems. Fans prevent damaging condensation by diluting muggy air and circulating drier outdoor air.

Power attic ventilators with built-in humidistat controls run faster when humidity is high. This further enhances their ability to actively lower moisture levels.

Can roof exhaust fans lower air conditioning costs?

As discussed previously, properly installed and sized roof exhaust fans can significantly reduce air conditioning costs in warm weather. There are two main ways this occurs:

1. Attic heat reduction – Removing hot air directly lowers attic temperatures, reducing heat transfer into the living space. This means ACs don’t have to work as hard.
2. Preventing issues causing energy loss – Ventilation inhibits moisture, mildew and insulation damage. This prevents energy leaks making ACs run longer.

DOE studies found that enhancing attic ventilation can lower air conditioning costs by 10-25% per year. The Florida Solar Energy Center saw AC savings of up to 17% in homes using power roof ventilators.

Savings vary based on climate, home construction, fan model and use. But properly installed roof fans consistently demonstrate reduced cooling costs over homes without them.

Do roof exhaust fans add value to a home?

Installing a roof exhaust fan can potentially increase a home’s value in two main ways:

1. Lower ownership costs – Reducing utility bills makes the home more affordable, attractive to buyers.
2. Prevent deterioration – Ventilation prevents moisture, humidity and heat issues that can degrade home materials and structure over time.

In addition, exhaust fans provide benefits like cooler temperatures, lower humidity, fresh air, and improved air quality. These can make a home more comfortable and healthy for occupants.

Homes with features that improve comfort, indoor air quality and operating costs tend to have higher resale values. As an inexpensive upgrade that accomplishes all of this, roof ventilators can be a smart investment when selling.

Conclusion

Roof exhaust fans offer a wide range of benefits, from cooling attics and lowering AC costs to preventing deterioration and improving indoor air quality. While fairly inexpensive to purchase and install, roof ventilators can generate significant savings and added comfort over their lifespan.

Carefully following sizing, location and installation guidelines is crucial to maximize performance and return on investment. But overall, adding roof exhaust fans is an extremely cost-effective way to enhance ventilation and reduce humidity and heat buildup year-round.