History of Duck Tape

Like many others, I have assumed for years that the original and proper spelling for the ubiquitous gray cloth tape is duct tape, as in taping duct seams. I was wrong. I just recently learned some of the history of the original invention of Duck Tape by reading about it on a Facebook post by George Lanthier. If you work in oil or gas heat in the northeast, you probably have at least heard of George.  I know he knows what he is talking about, but we are talking about a Facebook post, so I did a little more research. According to Educationalnow.com, the word duck comes from the Dutch word "doek", which means linen canvas. According to thoughtco.com, soldiers called it “Duck Tape” because of the way it repelled water. Perhaps both are true. But that is not really the interesting part of the story.

A mom named Vesta Stoudt came up with the original idea for Duck Tape while working in a factory packing ammo boxes. Before the development of Duck Tape, cartridges were packed in heavy cardboard boxes that were taped and dipped in wax to make them waterproof. The box flaps were sealed with thin paper tape, and a tab of tape was left loose so that it could be pulled to release the waterproof wax coating and open the box. The problem was that the thin paper tape wasn’t strong enough, and the tabs frequently tore off when soldiers pulled on them to open the ammo boxes, leaving them frantically scrambling to claw the boxes open while under enemy fire. Vesta developed a prototype cloth tape to solve this problem. She had a personal reason for her concern about the effectiveness of the ammo box sealing method, she had two sons in the Navy.  Unable to convince her supervisors of the merits of her idea, she wrote president Roosevelt. President Roosevelt and his military advisors liked Vesta Stoudt’s idea, and they asked the Industrial Tape Corporation, a division of Johnson & Johnson, to develop and manufacture a cloth-backed, water-resistant tape with a strong adhesive. Duck tape was made with a layer of cotton canvas (doek) coated in waterproof polyethylene, and a layer of strong rubber-based adhesive. 

Soldiers returning from the war found all sorts of uses for Duck Tape and its usefulness made it popular. Duck tape was not used for duct work until after World War II. Unfortunately, the original style Duck tape is not actually recommended for use on duct work. It tends to dry up and become brittle. However, there are many other practical uses for general purpose Duck Tape.  Manco, now part of ShurTech Brands,  trademarked the name “Duck Tape” in 1980. Today, any tape actually named “Duck Tape” is from ShurTech. Now there actually is tape designed specifically for sealing ductwork, and it is referred to as “duct tape.”  Tape used with ductwork should have a UL 181 rating. The next time you hear someone mention “Duck Tape,” just realize they are being historically correct.

Using Manual D Speed Sheet

The free ACCA Manual D speed-sheet makes properly sizing residential duct work really easy. However, you need to complete three important steps BEFORE you are ready to use the Manual D speed-sheet. You must first do a Manual J room by room load study, select the specific equipment you will be installing, and draw out your duct system in stick form. The speed-sheet will help you size your ducts according to the required heat load in each, the unit output, the unit airflow, and the external static pressure requirements of the unit. There are three basic steps: determining the total effective length of the duct system, determining the design friction rate, and finally sizing the duct.

Effective Length
Manual D looks for the worst case duct run and bases the design friction rate on that longest run. The idea is that if the blower can move the air through the longest run, it can easily push the air through the other ducts. The assumption is made that each run will have a balancing damper, and that the balancing dampers will be used to balance the system airflow once the system is installed. The speed sheet gives you four columns to use for determining the longest effective length. You don’t have to use all of them if the worst case run is obvious. Note that you are NOT entering data for every run, just looking for the longest run.

There are three rows labeled Trunk. They are there for systems which have multiple branching trunks. Most systems will only use one.  Enter the length of the trunk duct from the plenum to the branch takeoff in one of the Trunk rows. Then enter the length of the branch run beside Runout Length. The second set of rows on this tab are for entering the equivalent length of all the fittings. They are arranged in groups of fittings with similar functions. Click on a group to go to the tab showing the different fittings. Choose a fitting that best matches the fittings you will use. You will need to remember it, or jot it down. Click return to return to the Effective Length tab. You will probably NOT have a fitting for every group. Just leave spaces blank which do not apply to your system. Repeat the process for the return. Note that the group numbers change bit because the equivalent length of return air fittings varies from supply air fittings.

Friction Rate
The second tab is for determining the design friction rate. You need to know the specific unit for this part because you will be entering the unit airflow and external static pressure. The idea is pretty simple. All things that the air moves across cause a pressure drop. You list the pressure drop in wc for all the air components. This is totaled and subtracted from the system external static pressure, and what remains is available static to be used for moving air through the ducts.

Since friction charts are based on 100 feet, the friction rate, or wc friction drop per 100 feet, needs to be determined. For example, if your available static was 0.12 and your total effective length is 200 feet, the design friction rate would be 0.06. A duct which would cause a pressure drop of 0.06 per 100 feet would create a total pressure drop of 0.12 by the time the air traveled 200 feet. The speedsheet does this for you based on the total effective length calculated on the Effective Length tab.

Duct Sizing
You need to have a Manual J calculation of the heating and cooling loads for each room before using the final tab, Duct Sizing, Simply list the room name, heating BTUs and cooling BTUs and the speed sheet calculates the duct size based on the friction rate and CFM from the Friction Rate tab. Note that it re-sizes the ducts every time you enter more data – so don’t be alarmed if it tells you the first room you enter requires a 16 inch run. The sizes are not accurate until you have all the room information in.

Trunk sizing is as easy as clicking a box for each branch duct that t trunk feeds. Note there are probably more rows for trunk ducts than you will need.  Returns are also sized the same way. You click the box of each supply run which you believe will be served by that return. This is obviously not an exact science. However,  it is important that each supply run is selected in a return. If you have return trunks, you size them by selecting the return branches which feed into the return trunk.

Creative Application of Manual D Speed Sheet
You can use the Manual D Speed Sheet as a teaching/learning tool by varying some of the entries. For example, play with different equivalent length fittings to see the effect between best case and worst case fittings. Try different external static pressures and airflows to see the effect on duct sizing. Thi is a great way to see the effect different design decisions can have on the end result.

Duct Cleaning Cuts Allergies

Occasionally I have a "guest speaker" provide the weekly article. This week, Gary Arena provides a some insight into the benefits of duct cleaning. Enjoy.

Allergies
Allergies can be a serious problem for someone’s overall health. The high concentration of pollen has been at an all-time high this summer, and overall allergies are increasing each year. Sensitivities to mold, mildew, dust and dirt can make everyday life a struggle. When a home air adaption is supplying air that contains these allergens, life can be quite miserable.

Benefits of Air Duct Cleaning and HVAC Restoration:
By removing this containment from a home air adaption, the effect is greatly reduced. Clean, healthy, circulating air is a must for those highly sensitive people. It is not unusual for a person to realize immediate relief upon completing a cleaning of a home heating, ventilating, and air conditioning adaption.

 
Here are the top 9 triggers that contribute to asthma attacks and allergy symptoms:
1. Dust Mites

2. Mold

3. Second-Hand Smoke

4. Cockroaches and Pests

5. Pet Dander and Hair

6. Wood Smoke (solid burning fuels)

7. Outdoor Air Pollution

8. Nitrogen Dioxide (from gas burning appliances and utilities)

9. Chemical Irritants

When dirt and debris are removed from ductwork, the fans and motors that power a furnace no longer need to work as hard to distribute air. Advising people to routinely get their air ducts serviced and inspected is important. Not only does this properly maintain a building, but it keeps the quality of indoor air as pure as possible!

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Written by Gary Arena from DUCTZ of Greater Lancaster and York Cities. Gary is the owner of the professional air duct cleaning company in central PA and is proud to serve a locally and family-owned franchise.

Tape is Tape NOT!

I must admit that when Glenn Walter of Shurtape offered to do a presentation on duct tape application for my class I thought “Oh HOW exciting!” (Yawn) After all, how much can there be to know about duct tape? It can’t even connect to the internet! But then I really hate to turn away help and I like having people from the industry come talk to my students, so we set up a class. One thing I have come to understand about life in general: whenever I think there is nothing to know about a particular subject, it is only because I know so little I don’t understand how ignorant I truly am. When Glen started his presentation I quickly realized that there is whole lot to know about duct tape. What follows is a cliff notes version.

Duct tape consists of a backing and an adhesive joined together. There are four types of backing: cloth (the old standard), film, foil, and foil-skrim-kraft (FSK).  There are two large categories of adhesives: acrylic and rubber based. Most techs know that codes require UL 181 tape. However, did you know that there are two general categories of UL 181 tape: 181-AP and 181-FX.  AP is rated for use on rigid ductboard and FX is rated for use with flex. Note that there is no specific UL rating for tape on metal duct systems – UL 181 is for ducts made out of manufactured materials. You may have also seen tape with a UL 723 rating, which is a smoke and flame spread standard. It makes a difference WHICH UL rating your tape has. Just because you see UL does NOT necessarily mean your tape is correct for the job. Even two tapes with the same UL rating can have different application specifics. Also note that the UL rating is not based on the backing or adhesive, but the tape performance in specific tests. Shurtape has 181-FX tapes with foil, film, and cloth backing with both acrylic and rubber adhesive. They are all approved for use with flex duct, but each has a specific application where it is better. For example Shurtape’s film backed tape with acrylic adhesive is rated for application between -20°F and 220°F. Their other FX rated tapes won’t stick at -20°F.

Most codes now require mastic for sealing metal ducts, but many people still use tape underneath the mastic. Did you know that many duct tapes are not rated for that use? Mastic does not stick well to film tapes. Not all cloth tapes play well with mastic because the chemicals in the mastic and the chemicals in the tape adhesive may not be compatible. The cloth tape might turn loose, then having the tape underneath the mastic just creates a place where mastic is not fully adhered to the duct. Foil tape usually does fine under mastic.  You should check with the tape manufacturer before using a tape underneath mastic.

Finally, the tape application is not complete until you apply pressure. For foil backed tapes, a plastic tool with a stiff rounded edge is preferable for working the tape into the duct. The pressure is needed to fully activate the adhesive on the tape. The adhesive undergoes a chemical process, similar to glue setting. Duct tape is not fully adhered until this process has been started through pressure application and completed with time. Believe me, there is a LOT to know about duct tape. If you would like to learn more, contact Glenn Walter of Shurtape at gwalter@shurtape.com