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Why Doubling Attic Insulation Does Not Cut Your Energy Use in Half

Some folks think that if the double the thickness of attic their attic insulation that it will reduce their heating and cooling bills by 50%. Doubling the R-value of the insulation in your attic does not cut your home heating bill in half. Here is why.

First, what is R & U all about?

Insulation is rated by its resistance to heat flow and is measured in units of R-value. The R-value is used in selling insulation because bigger is better.

It is easier to sell a product when bigger numbers mean it is worth more. It is harder to sell stuff to people, when lower is better.

R-value is an accepted product labeling number to make it easier for folks to understand that thicker is better. And, worth a higher price.

The inverse of thermal resistance is conductance, referred to as the U-value. The U-value is equal to one divided by the R-value (U = 1/R). Your remember fractions and algebra from school right? 

The U value is important to engineers because it describes how fast energy is traveling in or out of your house. It is the number we use in our heat loss calculations.

In the English speaking part of the world, we count U-values in Btu/square foot-Fahrenheit-hour. You don’t need to remember that. Just hold on to the idea that it is the speed of escaping energy, so lower is better.

So how do you use R-value?

R-value is intuitively easier to understand, the higher the R-value, the better the insulation. R-values of different components can be added. As an example if you have three layers of R 7 insulation in your attic the total R-value = 7 + 7 + 7 = 21

You cannot add U-values as easily. Watch out here come the fractions and decimals. Total U-value = 1/(7 + 7 + 7) = 1/21 = 0.048

Let’s see that visually

This graph shows the speed of escaping energy on the left. Squint so you can see the decimal point. The highest value is point 3 with zero at the bottom of the graph. The R-value is shown across the bottom of the graph.

Look at the graph and notice two things.

One. The speed of escaping energy is slowed a lot for each little bit of insulation until you reach R 14 where it turns the corner.

Two. From R 28 onward, there is very little improvement.

If you were to improve attic insulation from R-7 to R-21, for example, you could cut you energy losses through the ceiling by 65%.

Going from 1/7 versus to 1/21 U-value (or from 0.14 to 0.05) is a 65% improvement.

In most homes about 35% of the heat is lost out the roof, the rest gets out through the walls, windows and by air leaks. Therefore, the overall energy bill for the heating season would be reduced by about 23% (a 65% improvement of 35% of the heating bill.)

In this example, three times as much insulation saves less than one quarter of the heating bill.

The myth persists that, if R-11 insulation in your house saves heat and money, R-22 insulation saves twice as much. However, the energy and money you save by adding more insulation diminishes quickly.

Look at the graph again. Starting with an R-value of 3.5, every doubling of units in R-value cuts the speed of heat loss through the wall or ceiling by about half. The R-value points shown on the graph are selected because they are double the previous number.

As the thickness (R-value) gets higher, the speed of heat escaping through the ceiling soon becomes tiny. It reaches a thickness where adding more insulation costs more than it is worth.

So what do I recommend?

If the insulation in your attic is less than R 30 (9 inches or less of fiberglass) then you should add more.

Because the amount of labor to do the job does not change much with thickness, it is best to do the job once. By that, I mean add as much as you need in one new layer. Make it thick enough so that you will not have to do it again when the price of energy goes way up.

You should target a total of about R-50, plus or minus 10. The number does not need to be exact. R 60 is good for far North America. R 40 is good where the snow melts between winter snowfalls. If it hardly ever snows where you live, R 40 insulation will save on your summertime air conditioning bill.

I recommend going big and do it just once by adding one new layer of fiberglass. Use the thickest available single layer of unfaced fiberglass batt insulation that will get you near R 50. That is about 16 inches of total thickness.

The cost to bring in and set up the equipment for blown in loose fill insulation is the same no matter how deep you fill your attic. So, I suggest you shoot for a total of 16 inches deep.

Yes the material cost for thicker is higher, but by going with one new layer that takes you to a total of about R 50 you only pay the labor cost once. Or, if you do it yourself you only risk falling through the ceiling once.

That will give you plenty of insulation now and still do the job when the price of home heating fuel goes up.

Click here for a free money saving report written by the Energy Boomer titled HOW SAVE MONEY ON YOUR NEXT HEATING BILL

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HOW MUCH WILL I SAVE ADDING INSULATION TO MY ATTIC?

Folks want to know how much they will save by adding insulation to the attic of their home. The formula below will help you to estimate the cost effectiveness of adding insulation in terms of the "years to payback" for savings of heating costs. You can also estimate the savings per year.

Years to payback is the time required for the additional insulation to save enough fuel from heating (at present prices) to pay for itself.

The cost of the energy source is a key factor in determining payback. Energy prices vary widely from region to region, and from season to season.

Other factors, such as the rate of production and inventories of fuels nationwide, can also affect local energy prices. Also, the weather  varies, so your energy costs from year to year will vary as well.

To figure the cost of energy, consult your local utility for a rate schedule, or read your energy bills and plug your specific costs into the formula.

Get your paper and pencile ready.

Years to Payback =

       C(i) x R(1) x R(2) x E
  C(e) x [R(2) - R(1)] x HDD x 24

To calculate the payback, you need to supply the following information:

C(i)  =  Cost of insulation in $/ft². This cost per square foot should include the total cost of all materials, labor and equipment divided by the size of your attic. You need the square footage to buy the materials anyway.

C(e)  =  Cost of energy, expressed in $/Btu.

To figure the price you pay per unit, take the total amount of your bills (for oil, electricity, propane, or natural gas) during the heating season, and divide it by the total number of gallons, kWh, or therms you consumed during those months.

The following table provides estimated $/Btu prices:

 

E  =  Efficiency of the heating system. For gas, propane, and fuel oil systems, this is the Annual Fuel Utilization Efficiency or AFUE. Typical AFUE values are 0.6 to 0.88 for oil or propane furnaces, and 0.7 to 0.92 for natural gas furnaces.

Older systems are usually less efficient.

Use E = 1.00 for electric resistance heating.

For heat pumps, use the Coefficient of Performance, or COP, for E; where E = 1.6 to 2.4 for air-to-air heat pumps, and E = 2.8 to 3.5 for geothermal heat pumps.

R(1)  =  Initial R-value of section

R(2)  =  Final R-value of section

R(2) - R(1) =  R-value of additional insulation being considered

HDD  =  Heating degree days/year. HDD information can usually be obtained from your local weather station, utility, or oil dealer. I get HHD data from Weather Underground.com at http://www.wunderground.com

24  =  Multiplier used to convert heating degree days to heating hours (24 hours/day).

Here is an example to help you understand it

Suppose that you want to know how many years it will take to recover the cost of installing additional insulation in your attic. You are planning to increase the thickness of insulation from R-19 (6 inch fiberglass batts with moisture barrier on the warm side) to R-30 by adding R-11 (3.5 inch unfaced fiberglass batts). You have a gas furnace with an AFUE of 0.88. Assume a $1.10/therm price for natural gas and a cost of insulation of $0.18/ft².

C(i) = $0.18/ft²
C(e) = ($1.10/therm)/(100,000 Btu/therm) = $0.000011/Btu
E = 0.88
R(1) = 19
R(2) = 30
R(2) - R(1) = 11
HDD = 7,000

By plugging the numbers into the formula, you obtain the years to payback.

 

Years to Payback  =

 

     0.18 x 19 x 30 x 0.88
$0.000011 x 11 x 7,000 x 24

90.288  =  4.44 years
20.328

If the cost of natural gas increases to $1.30/therm, then the payback period is reduced to just under 4 years. Also, some additional savings will accrue due to reduced energy use during the air conditioning season.

Savings per year estimate

Divide the total cost of the project by the years to payback that you calculated above. The result is the estimated savings per year. The savings increase when the price of enegry raises.

Remember these are just estimates and can be a little off. Actually they are “eneginering estimates” not scientific calculations, but they do give you a good idea of the savings you will get.

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INSULATION BASICS

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INSULATING A HOME WITH BOOKS, MAGAZINES AND FABRIC

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INSULATION BASICS

Adding insulation is the most effective way of saving energy in most homes. Insulation works to slow the flow of heat through the ceiling and walls. It can also help by sealing air leaks. Adding more insulation will save you money during both the heating and air conditioning seasons.

Most types of insulation use air bubbles or trapped air to slow the flow of heat through the insulation. Air conducts heat more slowly than solid materials. Air trapped in the insulation slows the movement of heat.

The ability of insulation to resist heat flow is measured in units of R-value. Think of the R-value as, “Resistance” to heat flow. The higher the R-value the better the insulation does its job. The best air-filled insulations are rated about R 4.5 per inch of thickness.

There are three common types of insulation: fiber, foam, and reflective.

Fiber Insulation

Fiber insulation is available as loose fill or batts. Loose fill is generally fiberglass, cellulose, or rock wool that is blown into wall and attic cavities. It can provide better coverage than batts. R-values per inch for loose fill insulation are R-2.2 for fiberglass and R-3.2 for rock wool or cellulose.

A contractor using special equipment usually blows loose fill insulation into place. Some suppliers will rent you the equipment to blow the insulation into your own attic, as long as you buy the material from them.

I do not recommend blowing insulation into walls yourself. An experienced contractor is needed to avoid damage to the wall structure.

Batt insulation is easier to use for do it yourself projects. Batt insulation is available in rolls that are made to fit between the lumber in walls and ceilings. Rolled fiberglass batt insulation is sold in several different thicknesses. The R-value for fiberglass batts is about R-3.2 per inch of thickness.

Foam Insulation

Foam insulation comes as rigid sheets or as a spray. Rigid foam is generally more expensive than fiber insulation. It has higher R-values per inch than fiber insulation so it is a good value.

Sprayed foam insulations, such as low-density plastic foam, can achieve R-values as high as R-11 per inch. Most are spray foams are rated around R-5. Spray foams can help seal out drafts by blocking airflow and insulate at the same time.

Reflective Insulation

Unlike the other types of insulation reflective insulation, does not work to restrict conductive heat flow. It works by reflecting radiant heat away from where ever it was going. It works like a mirror.

Radiant barrier insulation is available in a couple of forms. The most common is a reflective foil made of two layers of aluminum foil. The layers of foil are put together with the shiny sides outward. Thousands of pinholes are punched in the foil to let water vapor through.

Reflective foil insulation should be installed with an air gap between it and any other materials.

Radiant barrier chips are pieces of lightweight reflective material. They can be blown into an attic as a topping over other insulation.

Evaluating the R-value of reflective insulation is difficult. Much depends on where in a building it is used. While it may have a high value of as much as R-8 in some applications, it is much less effective if relied on as the only insulation in walls or attics.

The Next Generation of Insulation

A broad array of new insulation types are in development. They hold the promise of offering values as high as R-20 or more.

One idea being researched is gas-filled panels. They use pockets of a low-conductivity gas such as argon, krypton or xenon.

Researchers are testing vacuum insulation panels. They rely on a vacuum between two layers of metal to create very high R-values. These work like a thermos bottle.

Aerogels are low-density fibers of silica or other materials. They can offer R-values as high as R-35 per inch.

Hopefully new insulation materials will be easy to use as well as cost effective.

Click here for a free money saving report written by the Energy Boomer titled HOW SAVE MONEY ON YOUR NEXT HEATING BILL

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EASY ADD ON STORM WINDOWS FROM THE INSIDE

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INSULATING A HOME WITH BOOKS, MAGAZINES AND FABRIC

If you live with a quilter, you know about a fabric stash. My wife has a huge collection of pieces of cloth that are too small to use. She keeps them stashed away in plastic tote boxes all filed by some color matching system that I will never understand.

To be fair her collection also includes some fabric samples that are large enough to use some day.

I do not complain as long as the fabric stash is pushed up against the walls of the house as insulation.

There also are several garbage bags full of fluffy stuff. They are the trimmings from the middle layer of many quilts. Filler, batting or what ever it is called. Some if these garbage bags of pieces too small to use have made three moves with us.

I do not complain as long as the above-mentioned material is pushed up against the walls of the house as insulation.

My wife also has 30 years, or so, of saved magazines. All saved because hidden in those pages is a quilt pattern that may some day make it to the book of “Quilting Projects to be Done.”

The “Quilting Projects to be Done” book is a three volume set now with about 100 projects in each volume. At a completion rate of, 10 or 12 projects a year, the backlog will last a while.

Stacks of magazines add to the insulation of the house, so I can’t say much.

The few walls that would otherwise be bare hide behind bookcases. The reason I can’t complain about the fabric and magazines is that most of the books in our collection are mine. When we moved out of our big house up North, I think that the count for my share of the books was something like 60 packing cases.

We have given away books. I have sold books. Some books were water damaged and black with mold and had to go. I still have many books that I have not read yet. I think that when you leave books in the dark too long they multiply.

Every once in a while we visit a fabric store or bookstore and purchase more insulation for our house.

Just think of the energy savings and extra warmth you get when you have floor to ceiling insulation made of your favorite things.

P.S from the Energy Boomer’s wife: Please note the basement is full of boxes of his model train supplies that insulate the walls!

Click here for storage boxes from Amazon

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How Much More Attic Insulation do I Need?

Generally, the more insulation your house has the more money you will save. You save during both the air conditioning and heating seasons.

60 million homes in the U.S. are estimated to be under insulated. By heading straight to the attic and adding insulation, homeowners can make their homes greener and save money.

Adding more insulation is the single most cost-effective way to reduce greenhouse gas emissions.

In the heating season, insulation reduces both your electric bill and your fuel bill. If you have an all-electric home, your really need the maximum recommended amount of insulation just to keep the electric bill smaller than your mortgage payment.

The flow of heat is slowed down by insulation. That reduces the amount of heat needed per month from your fuel. It also cuts the electric bill by reducing the running time on your furnace blower or hot water circulation pump.

Spring and fall are the best times of the year to do the work when it is not too hot or too cold. As the seasons change, your work will start paying off immediately. You can plan the job and learn exactly what to do any time of year.

Remember, you get no benefit until the job is done.

Before you poke your head up into the attic, you will need some tools; a flashlight, a flash camera, a ruler or tape measure, and a zip lock sandwich bag.

Do not climb into the attic unless you know how to avoid putting your foot through the ceiling.

Your first step should be to look into the attic and answer three questions.

1. What kind of insulation is there now, take a sample to go in a zip-lock evidence bag.

2. Where is the vapor barrier located? Look for paper or plastic film. Is it beneath the insulation or on top? Is it missing? If it is there put a small sample in your evidence bag.

3. Make a note of how deep the insulation is. Notice if it is fluffed up or packed down.

While you are collecting evidence, take a couple of flash camera photos. Shoot one that shows the end wall of the attic. Shoot another one that shows the area at the eaves where the slope of the roof meets the side walls of the house. Finish the film if you have an old style camera like me.

Take a good look at the attic and decide if you are going to tackle this job yourself or hire a pro.

When you have your photos and evidence ready it is time to go talk with the friendly folks at your local building supply store. They will enjoy talking with someone who is as prepared as you are. Their recommendations will help you select the type of insulation. The big question is to decide about a vapor retarder. This is the reason that I am avoiding giving specific advice. The need for a vapor retarder and where it should go question needs to be decided on a case-by-case basis. Take your time and get good advice on this item.

Most likely, there is a vapor retarder beneath the existing insulation. If it is there, all you need to do is add insulation that has no paper face on it.

If there is less than 6 inches of insulation now you may have to add two layers. The first lays is to fill the space between the joists. The second layer is to build depth running the other direction across the joists.

The recommendation is an attic should have between 16 and 22 inches of insulation with a minimum total R-value of 49. To learn more about R-value and reducing home energy consumption go to the Owens Corning site with this link.

The labor needed to install insulation is about the same regardless of the thickness you are adding. I recommend that you add the thickest blanket of pink fiberglass insulation that you can.

That means add the 9-1/2 inch thick R-30 pink fiberglass insulation to what ever is already there. If you have 6 inches, add 9-1/2 inches running across the joists. If you already have 8 inches, add 9-1/2 inches. You get the idea. That may take the total to more than the minimum recommended R-49. When the price of fuel doubles, you will not have to climb back into the attic and do it again.

Remember the benefit is worth the hassle. For most of us adding insulation to what is already in the attic will cut the amount, we pay on the fuel bill and on the electric bill by a large percentage.

Click here for a free money saving report titled HOW SAVE MONEY ON YOUR NEXT HEATING BILL

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