What does Infrared actually tell you about your home?

Infrared Imaging, commonly referred to as IR, is a very useful tool for anyone practicing building science. It provides visual images that offer clues to what is happening, temperature wise, in the wall (or floor, ceiling, roof...).

Wait, that last sentence is rather, well, limiting. Doesn't IR see through walls?

No, IR isn't magic. It's simply making a best guess about the temperatures on the surface of the walls based on a lot of assumptions. The operator of the equipment has supplied some of those assumptions as has the manufacturer of the imager. The manufacturer made his assumptions based on solid physics and years of testing. The operator is making his assumptions based on what he remembers from his training and how he is interpreting the conditions of the objects he's imaging. This can be a weak link, and it's where most bad IR interpretation starts to go wrong.

That's the other thing. IR doesn't tell you anything, it gives you information that you need to interpret. The operator needs to understand the workings of the system that's being imaged or the images make no sense. I work with buildings and I'm comfortable interpreting IR images of buildings. Ask me to evaluate an image of a horse and you might as well flip a coin, I'd be way in over my head on that.

Still, IR is a powerful tool to have. Because of the relative speed of acquiring information and because it can present that information graphically it makes diagnosing problems quicker and better. Homeowners get a better understanding as well. Seeing the effect of missing insulation really brings the point home quicker than the proverbial thousand words of explanation.

Let's take a look at a few images. The first one is simple. We're looking at a ceiling on the top floor of a building. The attic above is cooler than the room and the sun hasn't warmed it up yet. This attic had no access so I had to base my interpretation solely on this image. Fortunately when the contractor made an access to insulate the area properly I was proven correct.

The fiberglass insulation is in batt form. One end of a batt is being held up by the can light in the picture and the cold air in the attic is getting under it to the drywall ceiling. This is a classic situation and all too common. But this had been in place for 12 years and until I came in with a thermal imager no one knew about it. If you read my post on gaps in insulation you know how bad this can be.

One of the most useful things you can do with IR is find air leaks. With a reasonable temperature difference between inside and out I can use the blower door to create airflow. Once the door has run a few minutes you can get images like the one below. The cold air flowing from the attic creates the cold (blue) streaks on the warmer surfaces. Not only are these powerful for illustrating the effect, an air sealing contractor can use this as a guide to what needs to be done.

Important note: Ask anyone offering air sealing if they use a blower door and IR to find leaks and confirm results. Working without these tools is like tying your hands behind your back.

Once in a while you run into airflow strong enough that you can see it without a blower door. Every building science professional I have shown this image to assumes I had the blower door running on a cold day. The temperature difference was 20 - 25 degrees between in and out. My blower door was still in the van, so what happened?

I was in the lowest level of a former barn converted to child care. The building was a tall 4 stories and a really good example of the stack effect in a building that is leaky at both the top and the bottom. Think what the airflow would be like on a really cold day!

Sometimes unexpected patterns show up. Below is a small section of wall in a half basement. At the very top right is the edge of the board that caps the wall that is against the concrete wall. (BTW, this should not be done the way it was, that deserves a separate post.) The lower left is just a chair that intruded into the image. The orange-ish section on the right is mostly undisturbed fiberglass insulation under drywall. The center area, with those dark splotches are tunnels and nesting cavities created by mice. We confirmed this by removing the drywall (wearing protective masks and clothing) and cleaning out the mess and damaged insulation. Excluding vermin is really important in buildings both for health reasons and because they can cause damage to insulation and structure.

All of the above information was inferred from the temperature of the surfaces I looked at. With the IR and knowledge and experience with buildings I got the right answers. Ask your prospective energy auditor how much experience they have with buildings. If they were selling cars last month will they be able to adequately interpret the information they gather? Having the tools doesn't give you the skills and knowledge to use them.

Sometimes you can have a little fun with IR. I worked on several child care centers over the past few years. It was the most fun I've had on any project I've done. IR is not ideal for portraits but I got a lot of requests from the kids (Take my picture! Me too! You took her picture. Take mine). This little girl had just been playing outside and she was warming her cold hands on her forehead.

I'm told that IR is commonly being used in some countries as a medical diagnostic tool. The only interpretation I was able to make was that she had been having fun.

When you get an energy audit don't forget to have your picture taken as part of the process!

Little gaps in insulation can let a lot of heat escape.

And I can prove it: q(Btuh) = U X A X ∆T! See, end of post. All done, fini.

OK, that's not fair let's look at some pictures.

This is a small gap in insulation. It is about 1 square foot out of an area of 75 square feet. The insulation is R19 and for the sake of argument we will say that it really is working as R19 The metal top of the fan box is close enough to zero that I will use that. So it would seem reasonable to say that the average R value is 18.75 [(19 X 74)/75].  That's hardly any difference, 18.75 Vs 19? Nothin!

Except that's wrong. Q(Btuh) = U X A X ∆T. "Q" is the total energy flow(measured in British Thermal Units per hour), "U" is the rate of heat transmission (in Btuh/square foot). "A" is the total area and "∆T" (Delta T) is the temperature difference across the surface in degrees Fahrenheit. "U" by the way is the the measure of the rate of heat flow. We just lost R though, where did that go?

Engineers and scientists measure the rate at which things happen. R value is how much that rate slows. Getting from "U" to "R" is easy, divide 1 by either and you get the other. R 2 = U 0.5. R 3 = U 0.33. R is handy as a marketing tool, the higher the number the better. That's pretty easy to understand. Also you can add R values, which you can't do with U.

So with our exposed fan above how do we figure the actual R value of the total area? Here's the formula: U(avg) = [(U1A1) + (U2A2) + (U3A3) .../ A(total). (BTW, does anybody know how to get proper math formulas with sub characters out of HTML?)

In the example above we have R 19 at U 0.0526316 and R 0 at OOPS, can't divide by 0, lets call the fan R 0.5 = U 2. We have 74 square ft times 0.053 = 3.922 plus 1 square foot times 2 = 2 which adds up to 5.922 which we divide by total area (75) and end up with an overall U value of 0.07896 which equals R 12.66. That is a big difference for missing one square foot of insulation.

Of course there are those joists in there, 16 inches on center, which have an R value of about 5.5, this is going to make things worse. I won't run the whole formula but in a simple framing system like this about 10% of the area is joists, so 7.4 square feet. Now we have 65.6 square feet at R 19, 7.4 at R 5.5 and 1 at 1/2. Result? R 10.9 at most.

See how fast it slips away? What if things were worse?
 

That's a big hole. I didn't calculate the effect because I knew it was coming out. The owners were afraid to run it so it just sat there as a hole in the insulation. It leaked a lot of air too.

Sometimes it just looks like a wall (or an electrical box) until you use the IR imager. Even if you can't see it the effect is still there. What can look like an innocent little gap is really robbing you blind.

Want another way to look at it? Let's start with an R 40 attic.  Lose one percent of your insulation, lose more than 25% of your R value. Lose eight percent and you only have 25% left. Makes you want to hurry into your attic and neaten your insulation doesn't it? Well, do a good job and don't forget about the attic hatch.

Insulation is like a practical pair of shoes. Not sexy but oh so comforting.

The price of solar electric panels, or photovoltaics (PV), is really low. Depending on the source I've seen price guidelines that range from $1.75 to $3.75 per watt installed. That's actually a huge range and part of the reason is that most installers quote costs AFTER incentives (Rebates, tax credits, local tax allowances, etc.) which vary widely by location. But, PV is still a good deal. So why wouldn't it be the first thing you do?

Well, for one thing I work mostly with conservation measures, so it's less work for me. A better reason might be very simple. Conservation, air sealing and insulation, will make you more comfortable, PV panels won't.

Aha! I saw your head turn. You like to be comfortable, right? I can do it for you and save you money. Those PV panel can save money but they won't make you feel all warm and secure on a cold winters night. Let's have a little chat about the least sexy part of this, air sealing.

Air sealing involves some really dirty work, see least sexy above. You climb into attics, move insulation raising all sorts of dust (you are wearing a really good dust mask aren't you) and seal every large, medium and small hole you can find. The temperature in the attic is probably between very hot and hotter-than-people-are-able-to-survive-at. All the sweating you are doing will make the dust you are raising stick to your skin. The good part is that when you come out of the attic you will feel chilly. Even if it's 95F and humid.

After the attic you can do the crawl space and/or basement which will be cooler, but could be nasty in a different way. All in all this is pretty unglamorous. But if you have eliminated most of the big drafts in your house you will be more comfortable (no cold air blowing over your skin) and saving money. The more holes you fill the more you save.

Insulation comes after air sealing. Almost always. Sometimes insulation is air sealing, but only if it is rigid and not fluffy. Depending on your choice of insulation you will be dealing with materials that are either itchy, dusty, or both. Unless it is rigid, then it will cost a lot more. And you will be back in the attic and crawlspace. YIPPEE!

So how will insulation make you more comfy? It will warm up the surfaces near you. OK, that's not the same as warming up you, but really it's better. Just a bit of physics, that's all. Heat behaves very consistently, it goes to cold. That is, a warm thing will give up heat to a cold thing. Since you're typically warmer than the walls and ceilings, or you should be, you will be giving up heat to them. The warmer they are the less heat they will take from you. That make you more comfortable. Simple right? Just not very sexy.

That's OK. Now that you're nice and comfy you can sit around and plan how you're going to get that PV system installed.

Questions or comments, or if you want to complain that I really dumbed down the physics just use the comment box below.

Radiant barriers are seldom the cost effective option, especially in the north.

This is the current perversion of a bit of science into over enthusiastic marketing. Radiant barriers can, when properly installed, reduce radiant transfer of energy. The question is whether this is the best use of your home improvement budget. In my opinion the answer is almost always a resounding NO!

Before we go any further download this information from the Oak Ridge National Laboratory (ORNL) http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&ved=0CF0QFjAE&url=http%3A%2F%2Fwww.ornl.gov%2Fsci%2Fees%2Fetsd%2Fbtric%2FRadiantBarrier%2FRBFactSheet2010.pdf&ei=MIY3UdahKsSo0AGfnYAg&usg=AFQjCNHP3S7G_7P2KLEhesLTMuIOId31NA&bvm=bv.43287494,d.dmQ

This rather dull fact sheet lays out the case for and against the radiant barrier in different climates, with savings estimates for several starting points. In short it finds that even in warm climates radiant barriers are not always the cost effective solution. Cold weather climates really offer little opportunity for savings.

Have you ever been approached by a salesperson for this technology? What was your reaction to the pitch? Leave me a comment below.