All You Need To Know About Solar Attic Fans

Are solar attic fans really worth installing considering the material costs and installation costs? What are the other hidden costs that are not visible when you purchase a solar attic fan?

As homeowners, we cannot buy something in the market just because it says it has some advantages. The sellers do their marketing to create that impulse in buyers implying that their product delivers what they promise.

It’s better to know what they say is true or not. But, to assess the pros and cons of a product, you need knowledge. So, let us dig in and do a fact check on what they say about solar attic fans and the reality.

Why do we need an attic fan?

Household ventilation has been a part of architectural designs since the great Egyptian civilization which was brimming with architectural excellence 5000 ago. The architects in that era have developed structures making sure that the building is naturally cooled by constant airflow.

The same concept has been revolving over generations and today we are using an attic fan to do the same thing.

What does the attic fan do?

• Do you know the story of the wind and the sun? As the story correctly represents, too much of sun makes it extremely difficult for us even to stay indoors. Countries in the tropical regions are facing the issue of having to live in increased temperatures. In addition, countries like Morocco, Tunisia, South Africa have extreme temperatures exceeding 50 ⁰C.

These temperatures are unbearable to human skin. The natural room temperatures in tropical countries are considered to be in the range of 260°C – 280°C(Room temperature – Wikipedia, no date). The temperature that’s felt on the skin in tropical regions is much higher than the nominal room temperature.

Not only the temperature alone but there is also another factor that makes the surrounding heated and uncomfortable to be in. That is the humidity. When the humidity is high, we tend to feel the temperature more on our skin. We tend to sweat a lot. Humidity makes us feel the temperature is higher than it is.

This phenomenon is not only present in the tropical regions of the world. In the summertime, most countries face the difficulty of having higher temperatures and high humidity levels.

People use attic fans to get rid of this uncomfortable feeling.

Attic fans reduce the chance of sweating due to high temperatures indoors. It does not have any magical powers, but it does it by forcing the airflow from the inside of the attic to the outside of the house.

When air circulation increase in this manner, the number of water droplets in the air (humidity) will reduce since they are pushed outside of the house from the attic. Then, cool conditioned air will be sucked up into the attic making the living area cooler.

So, you will not feel uncomfortable due to sweating inside the house. This is one of the reasons why attic fans have been an option for in-house ventilation.

This being the primary use of the attic fan, there are some other additional reasons why people use attic fans.

• According to research by Yu and Moore (2015), wood materials have higher degradation rates at high temperatures. When the temperature reaches close to 66 °C, the strength of the wood material goes down by 32% which is a considerable amount. Now, we know that the temperature hitting 50 °C is also very rare.

But what this research says is that there is some degradation due to heat. Although the wooden materials like roof sheath or plywood probably will not be degraded by 32%, it will surely degrade by some amount.

Although this is not a popular reason why people buy an attic fan, this is a very valid reason to consider.

• Third reason to use an attic fan is to reduce the condensation issue. Mostly we might misunderstand that water dripping through the ceiling is due to a water leak. But it is not really.

Obaidi et. Al. (2014) shows that we spend 87% of our lifetime within buildings. As humans, we output a lot of moisture into the air from our activities. It might be due to cooking, bathing, boiling, or even breathing.

All the moisture added to the air is heated. We know that heated particles only go one way.

That is upwards. Moisture moves through the ceiling to the attic and gets stuck in the attic. The temperature in the attic grows more than the temperature outside.

This will start condensation on the inside of the roof. After a while, you will witness water dripping down from the roof. The opposite of this will occur when it is the winter season.

In addition to the above, Yu and Moore (2015) further states that there are several other reasons like higher cooling costs due to heated attic and forming ice on the roof deck in the winter. These are not as popular reasons as the ones given above but they are compelling cases to get your attic ventilated adequately.

These are all the reasons why that the attic needs to be ventilated properly. What ventilation does is circulating air between the outside and the inside of the house. As a result, the attic will maintain the same temperature as the living space of the house and the outside. Attic fans are serving as catalysts to this very purpose.

But why aren’t attic fans that popular?

Although attic fans are an option to ventilate the indoors, they are not peoples’ first choice. Attic fans are not as popular as air-conditioners which serve almost the same purpose. There is a rationale behind this matter.

1. John et. Al. (1994) states that the grid tied attic fans might not be as energy efficient as they say. Although attic fans can reduce 10% of energy costs of air conditioning (Chiras, 2004), it’s energy consumption can be much higher.

Usually, the power of an average attic fan is close to 250W. If you use this fan for 24 hours a day, it means that the attic fan will consume 180 units (kWh) in a month to keep the house a few degrees cooler. This can be a major reason why attic fans are not that popular among people.

The research by John and Tooley (1994) on the effects of improper use of attic ventilation fans calls the installation of attic fans as “a solution looking for a problem”. They mentioned in their article that if you don’t properly fix the attic ventilation fans, you might end up increasing the cooling costs and heating bills of the house in the winter.

• Secondly, Yu and Moore (2015) also states that if the envelop between the attic and the living space is not sealed properly, it can cause problems like reducing the pressure inside the house. This might lead to negative pressure built inside the house which might affect gas burners and similar appliance. Also, if the air vents that takes air into the attic (soffit vent) is disturbed, there will be a pressure imbalance causing the ceiling to damage as well.

Given above are the main reasons why people hesitate to install attic fans as a home cooling mechanism. It can be understood that the first problem mentioned above is a default issue in the attic fan.

To work, grid-tied attic fans need energy. They get the energy from the grid, and it costs a lot. It is uncontrollable.

The second issue is controllable by us. In order to get rid of the second problem, we have to seal the envelope between the attic and the living space. Then we need to make sure the vent into the attic from outside is clear and the airflow is not disturbed.

But recent developments in solar attic fans might just be a solution to the first issue mentioned above. Solar attic fans are powered by a solar panel. The main difference of solar attic fan compared to the conventional attic fan is that it is not connected to the grid.

Solar Powered Attic Ventilation Fans (SPAVFs)

Yu and Moore (2015) have done research on the performance of the SPAVFs.

This experiment was done in a ranch-style house in Boone, North Carolina in the USA. The attic was around 1440 square feet of area. In this experiment, two situations were considered mainly.

1. Attic temperature without mechanical ventilation
2. Attic temperature with SPAVF

In the research experiment, they have built a solar-powered attic ventilation fan with the following specifications.

• Power: 30W
• Maximum airflow: 1550 cubic feet per minute
• Solar panel capacity: 30W
• Motor: DC motor
• Fan blade: 12 inches
• Base flashing: 24-inch x 24-inch (Yu and Moore, 2015)

In this experiment, under similar conditions, they have taken the solar irradiance readings, ambient temperature, and attic temperature readings for the given two situations above.

It was shown in the results that the attic temperature reduced from 3.9⁰C to 14⁰C after the introduction of SPAVF. Therefore, it is crystal clear that solar-powered attic ventilation fans also have the same effect on the attic temperature as the normal grid-tied attic fans.

Now we know that the effect of SPAVF and the grid-tied attic fan on the attic temperature is the same, let's see why SPAVF is a step ahead of the grid-tied attic fan.

The main difference between the grid-tied attic fans and SPAVFs is that the SPAVF is not connected to the grid. It does not use power from the mains to power the fan motor. Instead, it uses electrical energy produced by solar panels connected to it.

This means that the cost for 180 units consumed by a 250W attic fan is totally saved. This is a huge step forward in attic ventilation. You just have to bear the initial cost of the SPAVF and that’s it.

There are no other costs attached to it like grid-tied attic fans. Although the initial cost may be between $300 – $700, which is more than that of a grid-tied attic fan, it might be a good long-term investment.

Further, solar attic fans are run by direct current and not by main alternating current. This makes it easy to control the speed of the DC motor connected to the fan. In other words, SPAVF has the ability to change the rate of airflow which again can save more energy compared to the grid-tied attic fan.

When you calculate the return on investment using the Attic Breeze Energy Savings Calculator, the answer you will get is between 4 – 7 years. When you check most of the SPAVF products nowadays, you can see that almost all the manufacturers give generous warranties.

Most of them are over 20 years and some even give a lifetime warranty for their products. Therefore, a payback period of 4 – 7 years is quite good considering the benefits reaped out of it.

Unlike grid-connected attic fans, SPAVFs are much simple to install. The reason being that there is no connection to the mains at all. The product comes as a package. It includes four parts.

1. The motor, outer cover and the solar panel.

The DC motor, the outer cover, and the solar panel comes as a ready-made part making it much easier to install. The DC motor and the solar panel are selected optimizing the costs and the power. A monocrystalline solar panel is used generally to produce more power and it is already tilted in a particular direction to receive the maximum amount of sunlight possible.

The outer cover is usually made out of military-grade aluminum used in fighter jets to make sure that it does not rust or deform in any manner. The blades inside the fan are symmetrically built-in in order to balance the stress and reduce the vibrations projected into the roof. This part is the main part of the whole system.

• Stainless steel screws

• Sealant

• Flashing skirt with rubber membrane

How to Install a solar attic fan?

Step 1: The first step is to locate the place to install from the attic. Drive a screw in the center of the location penetrating the roof surface. From the top of the roof measure the circumference and cut a hole of adequate size to insert the fan with the solar panel.

Step 2: Lift the roof material (asphalt shingles/tiles) and insert the top part of the flashing skirt underneath the roof material. This is done to make the water flow over the flashing skirt without penetrating the attic through the hole.

Step 3: Squeeze the sealant onto the rubber membrane and place the fan with the motor and solar panel on it in such a way that no air or water will be penetrating from the outside wall of the fan.

Step 4: Use the screws to firmly fix the fan and the flashing to the roof.

It takes only simple four steps to install a solar attic fan. Nobody needs an electrician to do this. This is a DIY (Do It Yourself) work.

SPAVF Operation

The operation of the solar-powered attic ventilation fan is quite simple.

The main power source is sunlight. The solar panel will harness the sunlight and store in a battery (if available). The electricity generated is being used to drive the motor. The fan also consists of a power electronics control board. This is to vary the speed of the fan in order to control the airflow.

The speed of the fan is dependent on the temperature of the attic. The temperature of the attic is sensed by a temperature sensor connected to the control board, When the attic temperature exceeds a certain limit, the fan will start and with varying temperatures, it will vary the speed accordingly.

As a safety precaution, to reduce the chance of spreading a fire (in an event of fire) due to the SPAVF, a “firestat” is installed in some SPAVFs. This is done to reduce spreading flames in an event of a fire by shutting down the electricity supply to the fan.

Variety of SPAVFs

SPVAFs are available in different sizes. capacities, colors, and vents. Usually, the power of the motor in the SPAVF is between 10W – 40W. According to the power of the motor, the solar panel capacity might also vary from 10W to 40W.

The outer cover is made out of aluminum, and you can buy it in many colors that suit your roof.

SPAVFs for Thought

At the beginning of the article, we looked at why attic fans are important and why they aren’t very popular among people.

Although it is important to have an attic fan, one main drawback of the conventional grid-tied attic fan is that it is not cost-effective. It will increase the electricity bills significantly.

SPAVFs are different. They aren’t connected to the grid at all and hence there is no increase in electricity cost. The cost of the ventilation system might be high due to the additional solar panels.

However, the return of the investment is much better compared to the conventional grid-tied attic ventilation fan. The total cost will be covered within 4 – 7 years where you will have a warranty over 20 years up to a lifetime.

Warranty varies from one manufacturer to the other. But all in all, it sure seems to be a solid long-term investment.