Radiant Heat Barrier

Radiant Heat - Home Energy Savings

2009-06-19T20:19:00.001-07:00

Using radiant heat or radiant heat barriers is a great way to strengthen your homes overall wall insulation or attic insulation or both, and can greatly affect your overall home energy. Your home energy saving value is closely tied in with your home energy efficiency but they are not necessarily the same thing and many people try to fix one with the solution for the other. Confused yet? Read on..

The concept behind radiant heat and radiant heat barriers is simple: make the insulation that is already in your home work more efficiently from an energy standpoint that it ends up saving you home energy over the long haul. The problem that currently exists with today's attic insulation is that it is highly inefficient because of the fact that the ambient temperature in your attic during the summer is quite high, while in the winter time it is rather low. In each case the conductive value of this temperature transfers into the insulation material itself and reduces the overall home efficiency or home energy factor of your wall insulation or attic insulation. Many try to solve this problem by adding more and more insulation, piles upon piles and layers upon layers of attic insulation. The problem with this lies in the fact that during the hot summer months, the added layers of home insulation heat up as well and as hot as the original layer, and together as one giant fireball of heat it passes that hotness right down the ceiling and into your living spaces. This is an example of poor energy efficiency, not poor energy savings.

Back to the concept behind radiant heat: radiant heat is that heat that "radiates from" or through the material and passes onto other spaces. If you heat up a metal pan on the stove top and then pick it up without a hot pad, you will feel the heat that has transferred through the metal and into your hand. You will also learn some new curse words that you did not realize that you knew. The same thing happens with the insulation in your attic and walls: the heat from the exterior and sun builds up in those small oven like spaces of your home, such as the attic and the pockets between the rafters, between your wall studs, and in your floor if you have a sub-floor.

And when you think about it, all of these areas are directly attached to your main living spaces- your living room, your bedrooms, the kitchen and on and on. The radiant heat acts like heating pads surrounding you during the hot summer months, and it forces your cooling system to work extra hard in order to not only repel the normal heat getting in from the doors and windows but the radiant heat constantly snuggling up to your through your walls and ceiling. This is what radiant heat is and this is how it works it way into your house and ultimately, into your pocketbook. Again, radiant heat has to do with poor energy efficiency.

So if this is radiant heat then a radiant heat barrier would be what? Don't get ahead of me here, I am the author. A radiant heat barrier basically inhibits the radiant heat from transferring from one pocket to the next and hopefully, it prevents the heat from getting into your living space. No home insulation material prevents 100% of the heat or cold loss, but by containing the heat that is already existing inside of each pocket of your attic and walls, radiant heat has achieved a measurable home energy efficiency factor. Radiant heat barriers are typically reflective in nature, just like aluminum foil, so all that they do is to keep the heat off of your current home insulation by reflecting it back into the void space, such as your attic, instead of letting it constantly sink into the insulation. In this way, a foil radiant heat barrier can improve your home energy efficiency factor because it lets the insulation do it'd job properly. Any heat that comes into your attic or walls through normal conductivity is reflected back into the void space and effectively out of your living area. Most good reflective heat barriers can reflect between 90% and 99% of the radiant heat, thus rendering your home energy efficiency more effective.

This is the whole reasoning behind breathable spaces in your home such as the attic or the pockets between the walls - to allow the the air to breath in and out and among other things, prevent accumulation of moisture that could cause further damage. Most good brands of foil reflective barriers are perforated just for this reason, so that they can reflect the radiant heat without compromising the purpose of the pockets - to allow air to freely pass through so that the moisture does not build up.

Radiant Heat Barrier Installation

2009-05-23T19:19:00.000-07:00

Did you know that there are numerous ways in which radiant heat barriers can be installed in both an existing home and also a newly constructed one. All radiant barriers possess a minimum of one low emissivity (reflective) surface, either of which can be aluminum or a sheet or both. We express emissivity with a value between 0 - 1. We compare this to a black substance that has zero (0.0) reflectivity. A radiant heat foil barrier should be able to reflect about 90%, thus having a reflectivity of .9 or 90%. In order for the foil to work properly, it must be facing the the interior space.

The easiest method for radiant barriers installation is most likely when you build a new home, although if you want to you can still add a pretty decent radiant barrier to your existing home.

Basic Radiant Barrier Installation:
A basic after construction installation type is called over the attic style, and it generally involves laying the reflective barrier right on top of your current and existing insulation. If you are installing your own radiant heat barrier, be sure to read the manufacturer's instructions. You can place each sheet right on top of your current insulation, making sure that the shiny side is facing toward the interior of the attic space. Also, it is generally a good idea to let the individual layers of foil overlap one another at the edges instead of nailing or tacking it down to the ceiling joists. This will help you in the future in case you have to access some electric wiring or furnace ducts or cable wire or anything else that runs through your attic. Also, you must take care not to allow the shiny reflective side of the radiant barrier to directly touch your existing home insulation. You want to maintain a healthy amount of 'dead' area between the two types of insulation so that the foil does not do the opposite of what it is intended. If the foil barrier were allowed to touch your existing insulation directly, then it would simply transfer all the heat it is reflecting right down through the insulation and you would be counteracting the intended purpose.

A second method of installing a radiant barrier is to attach the radiant barrier foil sheets to the roof. You an use several different methods to do this and it really depends on what stage of construction you are in. If you are just constructing and doing the frame and roof job then you might want to consider attaching the foil radiant barrier to the underside of the roof boards. However, if you live in an already built home or you already have your roof decking attached, then you may want to look at option two: have the foil radiant barrier attached to the underside of the roof decking but between the rafters. Again, make sure to leave that all important dead space -- at least a good 1" to 3". Both ways are generally acceptable and will go a long way in reducing your overall energy bills. The addition of a radiant barrier in your attic can also make your furnace run more efficiently and last longer, especially if it is located in your attic, which many are.

Another way to install a foil radiant barrier is to put it in the walls as you build. Obviously, this is for new construction and must be planned for in the blueprints so that your contractor can work it into the job in the proper order. Even if you live in an existing home, installing a foil radiant barrier in your walls is a possibility if you use a professional. It can be a messy job though and an expensive one. Just keep in mind that you need to calculate what your total return on investment will be and when you will potentially break even. Often times doing the foil on the interior of the walls of an existing home is not cost effective unless you plan on living in your home for over 15 years. The radiant barrier should always be installed with the reflecting side facing the vented air space.

Another thing to keep in mind during radiant heat barrier installation is that your attic space must be adequately vented so that the house can breathe. This is a concern because the radiating foil will be reflecting or deflecting thermal heat from other areas in your home towards the space in your attic and you need to make sure that it can escape properly before it turns back into water moisture, which ultimately will lead to major problems such as the water vapor condensing and freezing and leaking. Consider this when you choose your building materials; you may want to select perforated soffits and otherwise well vented products.

Also, some of the foil radiant barriers are now equipped with perforated holes in order to allow the proper airflow. This is always an option be you will need to choose one that does not compromise on reflectivity as saving energy dollars is the main goal for the install.

Radiant Heat Barriers Properties

2009-05-06T19:27:00.000-07:00

Radiant heat barriers typically have either one or two sides of reflecting material and both versions work extremely well in preventing heat and cold home energy loss. There are various types and brands, but all will have this reflective quality and the good ones will have a few more features.

If it is installed directly on top of your current fiberglass insulation in your attic, then it is vital to have the reflective side of the radiant insulator facing the open air space of the attic.

Also, radiant barriers used directly on your attic floor must also be manufactured to allow water vapor to pass through. This is essential so that the natural water vapor that escapes from the living area outward does not condense and freeze onto the insulation. Several problems would ensue if this were to happen. It is not necessary to allow water to pass through, only the water vapor.

Many kinds of radiant heat barriers offer this feature, some using perforations throughout the material and others a different method. Although the perforated version is the easiest to make, be careful about those that have large holes or too many of them. These excesses will also allow heat and cold to pass through them thus reducing their effectiveness overall. Look for a brand that offers a passable water vapor element but also one that has the lowest emissivity.

Emissivity is measured on a scale of 0 to 1, with scores closer to zero being the best for home insulation purposes. The lower the score, the less heat or cold (overall energy) is being lost. If your radiant barrier has an emissivity of .09, then your insulation is reflecting 91% (know as reflecting value or reflectivity).

Look for a manufacturer that offers a high reflectivity (or low emissivity). A good number is around 96% to 98%. Again, perforated types are actually okay as long as they have a high reflectivity. Try to get second opinions about brand choices as the numbers published by the manufacturers are usually estimated in-house. Ask about potential home energy savings. Many will claim 30% to 40% but the reality is usually 10% to 15% savings. It does take time to measure this because seasons vary so much in their severity and so is can be hard to gauge the effectiveness of your insulating barrier, though, and usually by the time you have enough data to calculated your savings, the warranty is usually expired.

What are Radiant Heat Barriers?

2009-05-02T13:03:00.000-07:00

What is a Radiant Heat Barrier?

A radiant heat barrier is basically a membrane made of a reflective substance, normally used to deflect or reflect sunlight and heat. The most common uses are in the construction industry, where radiant heat barriers are being used and are starting to become more commonplace. You might even already have a radiant heat barrier on your house and not even know it. To be specific, radiant heat barriers are building materials that are being used in both commercial and residential construction as a means to insulate against heat penetration. The primary usage for residential heat barriers is in attics; helping to reduce the work that your air conditioner and heating system have to do. By insulating against the heat during the summer and against the cold in the winter, the radiant barrier can effectively shield your home from energy loss. Radiant barriers are not, however, a typical insulator.

Typical insulators rely on thickness or density or both in order to blanket the home's roof, attic, walls, or sub-floors. Radiant barriers, on the other hand, reflect heat away or deflect it back into the living space, thus reducing the overall load of your furnace and, theoretically, increasing efficiency. Think about it this way: if you live in a seasonally warm climate such as Texas or Arizona or Florida, etc, then your home is exposed to high quantities of sunlight and heat almost year round. Normally, that heat is concentrated on your roof face and penetrates (transfers) into your living space. Fighting against this invasion is only your air conditioning system. The heat has the free and mighty power of the sun behind it, your air conditioner has only a small amount of electricity, inefficiency, and your bank account backing it up. It is an unfair fight in most cases. The heat usually quickly succeeds in driving through the roof and into the attic. Unfortunately, most attics are designed in a such a way that they act like a oven- few openings, little circulation, a heating element (the roof and air), and a small tight "box" in which to build up heating momentum. And that is exactly what happens once this heat does penetrate - it cooks your home. Once inside the attic, it quickly surrounds, penetrates, and is absorbed by your attic insulation. Next, it gets into your living space and goes head to head with your cooling system. This is an ongoing battle and it is usually offset by forcing your air conditioning system to work harder. This, as you can guess, increases your energy bills as your HVAC system requires more and more power in order to fight off the harmful summertime heat.

Today's attic insulators are usually either normal fiberglass rolls that you normally see, or are the "blown-in" cellulose insulation, which is quite loose and not inhibited by the paper backing. Although both kinds are effective to a degree, they each lack the true ability to prevent the heat from getting into your living space. This is because it is up against RADIANT heat - it radiates through the airspace and everything around it - like water but without the weight of water. And in most all cases, the insulation in the attic only slows down the heat penetration. Radiant heat barriers take a approach but use a different and more efficient method. Instead of insulating the home with a quilt-like blanket, radiant heat barriers rely on causing the heat to turn tail and run. They act as mirrors, and once the heat hits this reflective film, it goes the other way. Often times, the amount of heat that actually reaches your living space can be reduced by up to as much as 50% when the radiant heat barrier is installed properly. This is a hugely significant amount of energy loss reduction. And, used in conjunction with traditional insulation, it can become a quite proficient means of protecting your homes energy and livability qualities.

Radiant heat barriers, however, reflect or deflect the heat and light. In the summertime, the radiant heat barrier can reflect the sunlight away from your home altogether or else can reflect it once it has already penetrated your attic. This depends largely on how it is installed, and there are a few options for radiant barrier installations. In the wintertime, radiant heat barriers can deflect the heat that your heating system has produced. It deflects it back into the living space, thus preventing it from escaping as lost energy.

How Radiant Heat Barriers Work

2009-05-02T12:33:00.000-07:00

How do radiant barriers work?

Radiant heat barriers work by inhibiting the heat transfer process that is characteristic of your roof and attic setup. Typically, the heat soaks into the roof and heats up your attic space, whereupon everything in it heats up, including your conventional fiberglass or cellulose insulation. Once the materials in your attic warm up, they start to give off heat themselves, just like if you were to put a pan in to a hot oven, after a while in there the pan would start to give off it's own thermal heat. And, to continue the example, when you remove the pan from the oven it keeps giving off heat. This is quite common and as matter of fact, more people burn themselves touching hot pans than do touching the hot oven chamber. That is because you cannot always see thermal heat, and therefore it is easy to forget which pans have been in the oven and which have not. This form of heat transfer is called "emissivity" and it is a quality of all materials. Scientists use a scale ranging from zero to one to determine how much thermal home energy any particular substance will give off; it varies depending on the material and the surface temperature (which is directly influenced by the ambient temperatures. And the same is true of the relationship between your attic heat and your living space heat. The roof heats up because of the hours and hours of exposure to direct sun. The heat transfers through your roof and begins to heat up your attic space and everything in it. Once that happens, then everything in your attic serves as a heat source, like hot lava on top of your ceiling.

This is where the real value of a radiant heat barrier really shows. Basically, the radiant heat barrier is able to deflect this thermal, or "radiant" heat. This is known as "reflectivity" and is also measured on a scale of zero to one, again with one being the high reading.

. For a material that is opaque (that is, it does not allow radiation to pass directly through it), when the emissivity and reflectivity are added together, the sum is one (1). Hence, a material with a high reflectivity has a low emissivity, and vice versa. Radiant barrier materials must have high reflectivity (usually 0.9, or 90%, or more) and low emissivity (usually 0.1 or less), and must face an open air space to perform properly.

When the heat from the sun penetrates your roof, a radiant heat barrier is able to reflect a portion of that (usually between 70% and 90%) back towards the roof and out, thus keeping your ceiling and insulation much, much cooler. In these cases, your air conditioning has to work much less vigorously. This is why we say that the radiant heat barrier reduces the stress placed upon your A/C system.

Under simlar conditions, a roof mounted radiant barrier can work by reducing the amount of radiation present on the insulation. Because the amount of radiation hitting the top of the insulation is less than it would have been without a radiant barrier, the overall insulation temperature is significantly lower and the amount of heat running throughout the insulation is also curbed.

Radiant barriers tend to also reduce indoor heat losses through the ceiling in the winter. Radiant barriers reduce the amount of home energy radiated from the top surface of the insulation, but can also reduce beneficial heat gains due to solar heating of the roof. The net benefits of radiant heat barriers for reducing winter heat losses are still being studied.