Issue link: https://read.dmtmag.com/i/133786
SERVICE & SET-UP This Duct Has Two Bills BY GEORGE PORTER Recently I attended a seminar on duct leakage. A person has to look around a bit to find this topic on the agenda of most meetings but there it was. Not two months later I found a use for the new knowledge. Sadly, it made me think about how much I must have missed in the last 30 years of fixing homes. You can learn new tricks even if you are an old dog. Here was the problem: The homeowner complained about walls turning black. All the electric switches and the main electric panel box had wet, soft drywall all around them. What I would have thought was that the area under the home was wet and for some strange reason it was settling mostly on the walls of the house. The floor was not too bad, mostly out of level because of the mud, but not rotting like the walls. I would have figured it was weird, but it was caused by the wet area under the home and a serious lack of ventilation. Yes, these things existed and they were bad problems, but none of these items after they were corrected would have changed the wall problem. The wall problem was absolutely 100% a product of duct leakage under the home. Here's an experiment for you to try. Get a paper bag and blow it up like you were going to pop it with your hand. Don't pop it, just suck a little air out of it and see what happens. The bag will collapse back down to flat just like it was before you blew it up. Now blow it back up and take a sharp pencil and poke two or three holes in the bag. Blow into the bag and your air will leak out the holes but, gently inhale on the bag and instead of collapsing like before, a lot of air will come back in the holes you made with the pencil. Houses work the same way. If you pull or push air out of a home then there has to be some air to replace the air you took out or the home will collapse. The caving in of a home is impossible because of the hard framing, but the pressure of the outside air trying to get to the lower pressure inside the home is enormous. It will find a way and the area of least resistance is around openings in the outside shell of the home. One wall is only half as hard to get through as two walls so when air gets through the outside wall it looks for a hole in the inner wall. The easiest openings it can find to leak through are the light switches, electric outlets and the main breaker panel. The marriage wall mating gasket was not all that tight, plus, these walls have outlets etc. on both sides. This marriage wall was drawing its air from the wet area under the home so it was the most damaged. I knew that this was the problem when I heard about it over the phone because it was exactly what the guy had talked about in the seminar even though he was talking about hotels and restaurants. (Note) Restaurants have a big problem with this because of the giant exhaust fans over the stoves. They push thousands of cubic feet of air out of the building a minute and thousands of cubic feet of air has to come into the building to replace the loss. It affects the heat and air and much engineering is done to keep a correct balance in the structure. You can learn new tricks even if you are an old dog. JUNE 2013 20 THE JOURNAL When I visited the home this summer in a southern state the very first thing I did was to crawl under the home. Sure enough, the crossover duct was blowing the torn plastic and insulation around the openings like flags. This duct had two bills because the homeowner was paying for all the cool air he was blowing out of the crossover duct and he (or someone) was going to have to pay for repairing all the walls that were damaged. The air conditioning bill will be by far the lower of the two. It may be hard to imagine that a little hole in a crossover tube could ruin a whole home but it certainly is possible and it can take less than a few months under the right conditions. If you are an installer, or a dealer that has an installation crew, this duct bill could be yours if you don't take care to make the crossover secure and leak free. If your homes don't have big hoses under them then don't start to think that this does not apply to you. Making a good seal on an in-floor duct at a marriage wall is a fairly tricky thing to do and it is a very hard thing to fix. You will never see the top of that seal again unless you take the home apart or remove a wall. Keep in mind that whatever you do the day you seal it up will have to last for the life of the home, or else there will be duct bills. T J George Porter is a consultant to the manufactured housing industry. His Company is Manufactured Housing Resources, P.O. Box 9, Nassau, DE 19969, (302) 645 5552, Web: www.george-porter.com. Some of his services are both in person and On-line training for certification in many states plus expert witness and investigation for the industry.