Best Way to Keep Attic Cool – 7 Energy Efficient Ways
Fixing the leaks and opening the skylights might help make your attic cool, but harnessing the sun’s power – transforming it from problem to solution – could be the answer to keeping your attic cool. But how can you keep your attic cool using the sun? Well, you can improve attic ventilation by installing solar attic fans.
You can keep your hot attic cool by improving ventilation, installing a cooling system, harnessing thermal reflection, and improving insulation.
Ventilation can either be passive or active. Passive ventilation relies on vents and thermal buoyancy (the expansion & rising of heated air and the relative density of cold air) to cool attics. On the other hand, active ventilation relies on the forceful movement of heated air by attic fans. And with a solar attic fan, you may use the heat from the sun to solve the same problem it creates.
A cooling system such as an air conditioner relies on a coolant to transfer heat from the air in the attic outdoors. While the degree of attic cooling with such a system is significant, the energy bills may also be huge.
Attic cooling using thermal reflection depends on redirecting thermal energy as it hits a reflective surface. It is a pretty straightforward process that tries to keep heat from getting into the attic in the first place. Insulation works like a thermal reflection in that it keeps heat from entering the attic. However, unlike thermal reflection, insulation keeps heat away by blocking conduction.
#1 Passive Ventilation
Without proper passive ventilation, air will absorb heat, become heated, accumulate in your attic, and raise the temperature rapidly.
Passive ventilation is ventilation driven by natural forces. This type of ventilation depends on thermal buoyancy and wind to move warmer air out of a given space. However, for passive ventilation to be successful, you must install a passive vent such as a gable, ridge, or soffit vent.
While wind drives passive ventilation in an attic space by pushing hot air out the vent, thermal buoyancy works thus:
When the air gets warm, it becomes less dense and rises. In its ascension, it is replaced by denser, cooler air. The rising hot air escapes through the vent, while the heavier cold air takes its place and reduces the temperature of the attic space.
A gable is a triangular wall space formed when two sides of a ridged roof meet. This space typically comes with vents, but if yours does not, you may install one to cool your attic.
Gable vents are typically constructed by installing slotted siding or wood on the gable space. In many cases, the slotted piece of wood is installed on two gable spaces. But if you have more, you may install the vent on each space.
Ventilation facilitated by a gable vent is passive. So, its effectiveness largely depends on the presence of strong winds. In some cases, gable vents are combined with other types of vents (particularly soffit vents) for a stronger overall cooling effect.
Ventilation offered by a gable vent works in two main ways, depending on the direction of the wind. When the wind moves perpendicularly to the vents, one serves as the inlet, while the other serves as the exhaust. Cool air comes in through one vent. Then warmer air escapes through the other.
However, when the wind moves parallel to the vents, both vents serve as inlets and outlets depending on the tide of the breeze. In this case, as warm air rises and leaves through the vents, the pressure falls slightly. The fall in pressure drives the entry of cooler air.
While gable vents are a valid way to keep attics cool, they are not recommended for installation in houses exposed to driving rain. This exposure to rain leaves the attic at risk of accumulating excess moisture, which will cause damage. Hence, the non-endorsement.
Over time, a gable vent may accumulate debris, dust, nesting materials, or the remains of pests. When this happens, they will become clogged and closed to airflow. To avoid this, ensure you clean the vents on a regular and repair them when you must.
Should Gable Vent Be Used With Ridge Vents?
If you can, do not combine a gable vent with ridge vents. Both types of vents are installed at almost the same level. This means the air they will draw in or push out will be almost at the same temperature. So, even if the gable vent tries to act as an intake vent, it will not draw enough cold air to reduce the attic temperature.
In fact, using a ridge and a gable vent may lead to forming a stagnant layer of warm air close to the attic floor. Then the said layer of air may trap heat and moisture in the living space.
Soffit Vents (Brings in Cool Air)
The soffit is the area underside your roof’s overhang, and it is the space most used for intake vents.
Soffit vents are narrow slits installed in the soffit area. They are not readily seen and are not quite exposed to dust, debris, pests, and adverse weather.
Owing to the position in which they are installed, a soffit vent is also a passive vent – air flows freely into the vents. For this same reason, they mainly function as intake vents. So, if you intend to use a soffit vent, you have to install corresponding exhaust vents. Some exhaust vents you may use with soffit vents include gable vents, turtle vents, ridge vents, and turbines.
The exhaust vents to be installed alongside a soffit vent must be placed higher than the soffit vent. Else, the warmer air will not escape as expected.
So how does a soffit vent work with the exhaust vents? Well, as air is heated in the attic, it rises and leaves through the exhaust vents. This creates a slight negative pressure in the attic. Then this fall in pressure, in turn, draws cold air into the attic through the vents.
While a soffit vent is not quite exposed to dust, debris, and nesting materials, it can still get clogged. So, over time, if you notice that your attic space is getting hotter than usual, examine the vents. If they are clogged, you should clean them. However, if the vents are not clogged when you examine them, you may have to install more units.
Ridge Vents (Removes Hot Air)
Ridge vents are exhaust vents installed on the roof’s ridge (the highest point on the roof). They typically come as a single long vent unit or as multiple short vent units.
A ridge vent also works passively due to its position, size, and the spontaneous ascension of warm air. Naturally, as the air gets hotter, it rises. Then as it is rising, it finds a way to escape through the opening provided by the ridge vents.
Now, not everyone recommends using roofers, especially in a region that sees a lot of heavy rainfall. The position of a ridge vent makes for the potential entry of rain or snow into the attic.
Of course, if rain or snow gets into the attic, there will be a rise in humidity. High humidity levels will support the growth of mold and mildew, and these organisms, in turn, will destroy various items in the attic.
#2 Install an Attic Fan (How Attic Fans Keep Your Attic Cool)
Besides promoting passive ventilation, you can reduce the temperature in a hot attic by installing fans. Like the vents described above, these fans promote ventilation. However, unlike those vents, an attic fan drives ventilation actively.
So how do attic fans work? Remember we said air rises as it gets warmer and then escapes through an exhaust vent? Then as the hot air leaves, it causes a fall in pressure, which drives the entry of cold air. What an attic fan does is promote these processes.
Attic fans are typically used alongside exhaust vents, most commonly a soffit vent. They push hot air out of the attic, causing a fall in pressure. This fall in pressure alongside the pressure created by the escaping hot air promotes cooler air entry through soffit (intake) vents. So, in the end, you get a cool attic.
When using an attic fan, you must be wary of the possibility of cooling loss. Cooling loss occurs when the fans remove more air than the intake vents can replace.
When a cooling loss occurs, the fans try to compensate for the deficit in the incoming air. To do this, they draw cool air from your living area; when this happens, your cooling costs will rise.
To avoid cooling loss, check and clean your intake vents regularly. Also, ensure the attic is completely sealed from your living space.
Does the Size of the Attic Fan Matter?
Yes, the size of the fan you get for your attic space matters, but not only in the way you think. If you get a fan that sucks more air out than the intake vents bring in, the cooling loss may occur.
At the same time, if the fan is too small for your attic space, it will never push out enough hot air to make your attic cool.
So, while choosing a fan for your attic, ensure it is not too big or too small for the normal flow of air in the area.
Should I Use Attic Fans With Gable Vent?
You may use attic fans with a gable vent as the exhaust. But since gable vents are usually almost on the same level as the fans, they do not bring in a lot of cool air. Therefore, they will not be effective as intake vents when used with attic fans.
Types of Attic Fans
Turbine Attic Fan
The wind from the outdoor space drives a turbine fan (a turbine attic vent). It is typically installed around the ridge of the roof and comes with a capped cylinder with angle slits.
The wind goes in through slits and rotates the blades of the fan. The rotation of the blades creates a current of air in the attic that drives warm air outside. Cold fresh air comes in as a replacement with the hot air expelled.
Turbine attic vents are generally inexpensive. However, in the absence of wind, they will not function.
Electric Attic Fan
Unlike turbine vents, an electric fan is powered by the household current and is installed in the gable. As the blades rotate, these fans also push hot air out of the attic. While some never stop running, most are crafted with a thermostat.
The thermostat ensures the fan only comes on when the attic temperature reaches a specific minimum value. The thermostat also turns the fan off when it senses extreme temperatures. This way, if there is a fire, the fan will not stay on to keep it burning.
Solar Attic Fan
You could say a solar attic fan is an electric attic fan. However, unlike the conventional electric fan, it is powered by solar energy, not the household current. Also, a solar fan will not affect your energy bill, unlike the conventional fan.
Why Is Solar Attic Fan One of the Best Ways to Keep Attic Cool?
Like the other fans described, solar fans rotate to drive warmer air while making colder air. However, compared to the rest, it offers better energy efficiency, it is more eco-friendly and safer, amongst other benefits.
#3 Fix the Crack and Gaps
While trying to keep your attic cool, you must ensure no cracks or gaps in the attic.
With gaps, holes, or cracks in the attic, hot air will seep in during the summer, leaving the attic hotter. Through the same openings, moisture will seep into the attic. As we mentioned earlier, elevated moisture levels in the attic will cause damages such as wood rot.
If you notice any cracks or gaps in your attic, you should seal them. For those measuring less than 0.25 inches, sealing can be achieved with caulk.
When sealing such holes or gaps around the chimney, ensure you use heat-resistant caulk.
If the cracks or gaps are larger than 0.25 inches, you should seal them with an expandable foam spray.
#4 Install an Air Conditioning Unit
Installing an air conditioning unit is perhaps the most effective way to lower attic temperatures. However, it is also one of the most expensive options.
Apart from the cost of buying and installing the air conditioning, you may also incur increased electric bills. But in the end, the cooling you get would be worth it.
Installing an air conditioner to keep your attic cool is especially recommended when converting the attic to a functional space. An air conditioner keeps the attic cool, improves air quality, and keeps the whole house chill in the summer and warm in the winter.
If you intend to get an air conditioner for your attic, opt for a mini-split, ductless, or portable air conditioner.
As the name says, portable air conditioners can be moved around easily. They are generally small, and they come with wheels. Portable ACs stand alone. However, they must be vented to get warm, stale air out of the attic. They will often come with a window kit for the said purpose. If your attic has a window, installation is pretty straightforward. But if it does not, you may have to create a hole that leads outside for venting.
On the other hand, mini-split ductless ACs are not stand-alone. They come with an indoor evaporator cooler and an outdoor compressor, which must be connected through a line. However, unlike portable ACs, you only need a small-sized hole (about 3 inches) for the said line.
#5 Install Radiant Barriers
By installing radiant barriers, you dispel radiant heat before it is transferred into the attic space.
Radiant barriers are constructed with reflective materials such as aluminum foil. These materials basically keep the sun’s radiant energy out of the attic by reflecting them outdoors.
Besides aluminum foil, you may use oriented-strand board sheathing or foil-faced plywood as your reflective material. These two options are relatively more solid than aluminum foil.
When installing radiant barriers, let them droop in such a way there is no less than a 1-inch air space between the bottom of the roof and the radiant barriers. This space makes for effective radiation.
#6 Improve the Insulation
Proper insulation is vital to any effort you make to make your attic cooler. With the right attic insulation, you can spend 20% less on your heating and cooling costs. Appropriate attic insulation will also improve the overall energy efficiency of the house.
Insulation basically works by blocking the transfer of heat through conduction. So, as the radiant heat from the sun heats the walls and roof of the attic, the insulation materials shut them out from the attic space.
Some of the materials used for attic insulation include cellulose, high-tech foam, cotton, mineral wool, and fiberglass.
When insulating with foam, spray foam insulation is one of the most popular options, understandably so. Spray foam comprises polyol resin and isocyanate. When these 2 substances mix, they expand rapidly and create millions of air bubbles.
Spray foams block the 3 methods of heat transfer. For one, the space created by the air bubbles blocks conduction. At the same time, the air bubbles trap heat gained by convection. Then since the spray foam has bright color, it deflects radiant heat.
Beyond making your attic cooler, proper insulation helps maintain a fairly constant temperature in the attic. Then in winter, it can maintain warmth by trapping hot air inside the attic.
The Significance of R-Value When Insulating an Attic
When choosing an insulator, you should pay the most attention to its R-value. The R-value is a number that depicts how well an insulator can keep heat out.
The R-value of an insulator depends on the type of material, its density, and its installation process.
Generally, insulators with high R-value numbers are more effective at trapping heat. However, when trying to make your choice, these are the general recommendations:
- An insulator with an R-value of R30 is the best for hot climates.
- In mild or temperate climates, an R38 insulator would do.
- Then, in cold climates, an R49 insulator should work fine.
So, all in all, before choosing an insulator for your attic, consider the climatic conditions of your environment. Then consider your budget and the state laws. In some places, the law specifies the R-value and type of insulation material for use in attics.
#7 Install Reflective Roofing
Reflective roofing works in the same way a radiant barrier does. It keeps heat out of the attic space through reflection. And if the heat from the sun is reflected, the attic will not absorb it. Consequently, the attic will not heat up.
As with a radiant barrier, reflective roofing uses reflective material to dispel the radiation from the sun. However, unlike a radiant barrier, the installation of the reflective material is on the roof, not beneath it.
FAQ How to Keep an Attic Cool
Does a Hot Attic Make House Hot?
Yes, it does. As the attic gets hotter, there may be an accumulation of hot air around the floor of the attic. This, in turn, may lead to the trapping of moisture and heat in the living space. Consequently, the house becomes hotter.
As described above, the air conditioning unit will have to do extra work to keep the house cool when the house becomes hotter. Consequently, you may end up with higher heating and cooling costs.
Why Does My Attic Get So Hot?
As the rays from the sun travel towards your attic, they can heat the attic in various ways, including convection, radiation, and conduction. However, this will only happen in the absence of certain fittings.
For one, if the attic is not well-ventilated, the sun will heat it by convection. Then again, if the attic has no proper insulation or seal, it will absorb heat from the sun through the walls and the roof.
So, all in all, your attic gets so hot for the following reasons:
- Traps or absorbs too much hot air.
- It does not keep out enough hot air.
- It does not take in enough cold air.
How Hot Is Too Hot for Attic?
Generally, an attic becomes too hot when its temperature exceeds 130 degrees Fahrenheit or 10-20 degrees hotter than the outdoor temperature.
Benefits of Keeping My Attic Cool
- A cool attic improves energy efficiency and prevents steep energy costs.
- The air quality in a cool attic is generally wholesome.
- If your attic is cool, you will not have to worry about ice dams in winter.
- Of course, when your attic is cool, it becomes inhabitable. So, you can use it as a playroom, office, or extra bedroom.
- With a cool attic comes lower humidity. This, in turn, reduces the chances of mold and mildew growth. In the absence of the said organisms, you would not have to worry about wood rot.
- A cool attic makes for improved energy efficiency for your HVAC system. Since the HVAC will not have to do extra work, it can do more heating and cool with less energy.
- Cooling your attic also ensures your roof and shingles last longer. Prolonged exposure to high temperatures can shorten the life of the materials used in constructing your roof.
You might get the best cooling for your attic with an air conditioner or a solar fan. However, the best way to keep the attic cool is by combining the various methods listed above. All in all, keeping an attic cool is pretty simple. Once you understand the climatic condition of your environment and the principles of heat transfer, making the right choice should not be hard. However, if you are unsure of what to do, reach out to a technician.
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