Blowing Smoke

April 30, 2012
May/June 2012
A version of this article appears in the May/June 2012 issue of Home Energy Magazine.
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Long ago, when I started in this business, I wished for a pair of glasses that I could put on to see how the air was moving. (Now I wear glasses all the time just to see where I'm walking!) I still can't see the air movement without some sort of marker, like cobwebs, dust, or smoke. It is exceptionally useful for leak testing and combustion analysis to see how the air is moving, where it is going, and where it is coming from. Since we can't always get the spiders to build cobwebs where we need them, and dusty shafts of sunlight don't always penetrate into the basement when we are firing up a water heater, we need to rely on a device that creates a visible marker that can be carried around on the air currents.

Paul Raymer
is chief investigator of Heyoka Solutions, a company he cofounded in 2006. He has been wandering through the mysteries of building science since 1977. He has multiple BPI certifications and is a HERS Rater.

Air currents can be made visible with smoke, dust, or fog. To make smoke, you can burn something that will emit visible particulates, riding on the column of heated air, or you can create a chemical reaction. To create a dust cloud, you can whack one of the pillows on the living room sofa with a tennis racket or you can puff a packet of air through a dusty substance like talcum powder. To create fog, you can take a hot shower in a cold bathroom. The problem for the designers of smoke testers is to come up with some sort of contained air current visualizer that is easily seen, is as nontoxic as possible, is reasonably priced, leaves minimal residue, and responds on command. Not a small order.

Some of these devices generate a single puff or cloud that is carried along by the air currents. Some of them generate a constant cloud. So it is difficult to divide a constant source into puffs in order to provide a cost per puff scale. Since these devices are used to track air currents, in some cases a very short puff will get the job done. In other situations, like evaluating the air leaks around a window, a constant flow of air current visualizer is handy. I have chosen to arbitrarily divide the performance of these devices into relative, 30-second puffs to arrive at a puffs-per-dollar scale. Note that all of these devices are, or use, consumables that must be replaced—sort of like batteries or sensors.

I tested four devices: the Retrotec AC107, the Regin S201PR Powder Smoke, the Regin S220 Smoke Pen, and the Chimney Balloon Smoke Pencil Pro. My findings are summarized in Table 2 at the end of the article and are discussed below.

Right ImageChimney Balloon Smoke Pencil Pro. (Paul Raymer)
Right ImageRegin S220 Smoke Pen. (Paul Raymer)
Right ImageRegin S220 Smoke Pen. (Paul Raymer)

Retrotec AC107

This air current visualizer has been the workhorse of the industry for a long time. It is simple to use and very responsive. Inside the red Teflon plastic tube is a 10-ml glass vial of titanium tetrachloride (TiCl4). Bending the red tube until the vial breaks activates the tester. With the chemical activated, squeezing the tube will push out a puff of smoke.

The AC107 comes packed in a storage tube that includes an absorption packet, two cleaner sticks, two spare nozzles, and one extra rubber tube. The cap or nozzle seals the opening when the AC107 is not being used. It can be rotated and reinserted at the end of the rubber tube to provide a fine stream of smoke or removed entirely to produce a large stream. The AC107 has an unlimited shelf life before activation. After activation, the instructions say that it is "good for 1,000+ puffs or one year (with cleaning)."

The AC107 has no electrical component or lighting to illuminate the smoke flow, so under some conditions the smoke it produces can be difficult to see, but under most conditions the cloud is dense enough to serve the purpose. The AC107 functions by mixing the TiCl4 with water vapor in the air surrounding the internal, broken glass vial. This produces a cloud of titanium dioxide (TiO2) and hydrogen chloride (HCl). When TiCl4 comes in contact with water vapor, it rapidly forms other compounds as well; these include hydrochloric acid, titanium hydroxide, and titanium oxychlorides. All of these compounds are hazardous. Although TiCl4 breaks down rapidly in the air, you should take care when handling it. The AC107 instructions include handling warnings as well as a complete MSDS (material safety data sheet). It is always a good idea to read the instructions. The smoke shouldn't be directed toward electronics or metals, for example, because it can be corrosive. Make sure that there is no leakage from the container into your tool bag.

Because the Department of Transportation considers the AC107 a hazardous material, it must be shipped as such, which makes shipping difficult and expensive. Buying just one tube is as complex as buying 25. The cost of one tube shipped alone is $337.50. The cost of each tube in a pallet of 25 is $50.20 (including shipping). After January 1, 2011, the AC107 became difficult to find. See Table 1 for my ratings on the AC107 and the other devices.

Regin S201PR Powder Smoke

Regin is the exclusive distributor of smoke products manufactured by Bjornax, AB, of Sweden. The S201PR Powder Smoke is comprised of a plastic bottle with a snap top mounted in a base connected to a rubber hose that is connected to a rubber bulb. Inside the plastic bottle is a pulverized silica chalk powder. When the cap on the bottle is opened and the bulb is rapidly squeezed, a puff of dust is emitted that is light enough to float on airstreams and then dissipate, mixing with other dust particles in the air.

The S201PR is simple enough to use: Take it out of the package, open the cap, and squeeze the bulb. It is certainly responsive; the more aggressive the squeeze, the bigger the dust cloud. Pointing the bottle down and puffing, however, causes a glob of dust to be emitted. The particle cloud is a very fine dust, so it is not always easy to see. It is nontoxic and odorless. The particles are lighter than air and naturally sink. The initial container is relatively expensive, but the refills will bring down the long-term puff-per-dollar cost.

Regin S220 Smoke Pen

The Regin S220 Smoke Pen looks like a pen. It is 5¾ inches long, and it has a black plastic cap at one end and a silver push button at the other. Removing the cap provides access to the wick jaws. Before first use, you insert the wick into the jaws, allowing the wick to extend about 3/8 inch beyond the pen. The kit comes with the pen and six spare wicks in a plastic carrying case.

To use the pen, you light the wick, let it burn for 10–15 seconds, and then blow it out. The wick will continue to smoke until it is completely burned or until the cap is replaced. The wick is pure cotton coated with stearic acid, a waxy solid that allows the wick to continue to smolder after the flame is out.

The smoke is a thin stream that works well in relatively gentle airflows. It is generally easy to see in most light conditions. It has an odor that irritates some people and could be objectionable to a homeowner, although it isn't much stronger to my nose than an extinguished candlewick. It is important to remember that, although it is a tool, the Smoke Pen is burning. Don't put it down anywhere before it is extinguished—but it is much easier to extinguish than an incense stick.

Since the smoke stream is continuous, Regin breaks the cost down into 30-second burns; it estimates that you can get 360 of these burns from each wick.

Table 1. Device Ratings
Right Image
Table 2. Smoke Tester Summary
Right Image

Chimney Balloon Smoke Pencil Pro

Unlike the other products described here, the Smoke Pencil Pro runs on batteries. The manufacturer highly recommends that you use rechargeable batteries, because they will extend the life of the unit. The Smoke Pencil Pro can be purchased separately, together with a 3-ounce bottle of smoke fluid, or in a field kit that includes seven alkaline AA batteries (six for the base unit and one for the adapter tip described below); a 3-ounce bottle of smoke fluid; adapter with two tips; a Phillips screwdriver; an extra bottle top; extra nozzle instructions; and a carrying case.

Begin by installing the batteries. Then insert the smoke fluid into the FILL chamber. Squeeze the power/vapor lever gently to illuminate the LED power light and allow the vapor generator to heat up until a thin stream of smoke starts to flow from the vapor chimney. A large cloud of smoke is produced when the lever is pulled in firmly and then released. The lever can be pulsed in this way to keep a steady stream of smoke flowing. Don't grip down hard on the vapor lever; this can cause the system to malfunction. Read the instructions and practice until you get it right. Operating this device effectively takes some finesse.

The fluid is a mixture of high-purity, food grade, kosher USP propylene glycol; glycerin; and distilled water. It does produce a condensate that is supposed to run back into the EMPTY chamber, and the chamber should be drained when the unit is refilled. It can be sticky if it drips or overflows. The LED is a nice touch, providing some needed illumination to the smoke in dark corners. The adapter tip is another nice touch; it contains a very small fan that forces the smoke stream through a narrow cone tip for a narrower and denser stream. The on/off switch on this attachment is subtle, and since you can't hear the fan at all, I have personally left this switch on and totally drained the battery.

learn more

Download The Agency for Toxic Substances and Disease Registry's fact sheet on TiCl4.


Until recently, the Retrotec AC107 had the energy efficiency market pretty well sewn up. Most competing products were created for laboratory applications and did not work well as a buildings diagnostic tool in the field. But competing products have improved. It is very important to be able to visualize the airflows when setting up a house in worst-case conditions, looking for leaks with the blower door running, checking out the seams in a duct system, or checking for draft in a category 1 combustion appliance. Most of these things can be done in other ways. You can use a mirror to see fogging from combustion spillage. You can use a piece of toilet paper to sense the airflows in adjusting doors for worst-case conditions. A theatrical fogger is a great tool for exposing the leaks in a duct system. But having a reliable smoke generator is as handy as having a corkscrew for opening a wine bottle. It's the right tool for the task.

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