by Bill Smith, president of Elite Software

Computer technology continues to extend its miracles to more and more hvac professionals. One recent advance is new computer software for sizing gas vents for category 1 gas appliances. Young Supply Company, an hvac distributor in Saginaw, Michigan, has found that using software for sizing gas vents has provided substantial time savings and much greater precision in design. According to Rick Rhodes who handles insides sales for Young Supply, the software has also greatly improved customer service and boosted the sales of vent pipe.

With thirteen branches located throughout Michigan and northern Ohio, seventy five year old Young Supply is no stranger to the heating market and gas equipment. Young is often called upon to supply engineering expertise in sizing heating systems, vents, and connectors for both residential and light commercial projects. The good advice and design aid that Young offers, facilitates the sales of all kinds of hvac equipment, parts, and related supplies.

Rhodes notes that much of Young’s work involves retrofits where older existing chimneys need to be carefully reevaluated for the venting of modern high efficiency equipment. He observes, “The technology has changed dramatically from the old furnaces of twenty years ago that used monster stacks and large eight inch diameter chimney flues. Nowadays, with modern high efficiency equipment, you can rarely use an existing chimney as it stands. The new heating equipment is very prone to causing acidic condensation which can literally dissolve brick mortar. If the chimney doesn’t have a flexible liner or it has the wrong size flue tiles, in a few years, the chimney could be laying in the front yard.”

Rhodes explains more of the difficulties involved in vent sizing. “If you size the vent system too small, you can have real problems with the equipment not drafting correctly and operating inefficiently. Inadequate drafting can cause furnace gases and flames to roll out the front of the furnace creating a fire hazard. This can also cause carbon monoxide buildup as well. Poor venting on higher efficiency furnaces will often cause the furnace to ‘light hard’ resulting in more wear and tear on the furnace.”

Rhodes continues, “On the other hand, if the vent is oversized, flue gas condensation will drip back into the furnace and cause premature damage and corrosion in the heat exchanger and other furnace components. Oversizing commonly occurs when a contractor buys larger, more expensive vents in the mistaken belief that bigger is always safer.”

Rhodes recalls manual vent sizing procedures in the recent past. “Until 1993, we relied solely on the Gas Research Institute (GRI) venting tables as published in the American Gas Association (AGA) manual entitled, Venting Tables, Category 1 Central Appliances. On a typical job, a customer would come to us wanting to size a chimney vent system. I would help the contractor decide what type of connector to use with the chimney, either single wall or type B double wall. Next, we had to check whether the chimney was tile lined, and if so, was the internal area too big or too small.”

“Using the venting tables is usually straight forward, but there are lots of them and you’ve got to be careful to select the right one for your situation. The design precision is totally dependent on finding the right table in the AGA manual, and this is often a time consuming process. Complex systems with multiple appliances or systems with more than one furnace in a manifold were especially difficult to find in the manual.”

Modern heating equipment often requires small vent sizes so as to minimize the chance of condensation. Rhodes notes, “It’s not uncommon to have to use a metal vent liner on a fully tile lined masonry chimney that has too large an internal area.” In order to minimize costs, Rhodes would always first evaluate whether the internal area of the existing tile lined chimney was in the allowable range. This meant looking in the venting tables for the minimum and maximum allowable internal chimney area for a given btuh rating.

Rhodes felt like he was always having to design the vent system twice or more. First, the tables would be consulted for using a standard tile lined masonry chimney. If the existing internal chimney area proved unsuitable, he had to use the appropriate tables for type B double wall vents and then apply a derating factor of 20% onto the capacity values he read from the tables. If he had more than two elbows in the vent system, the capacity must be lowered by another 10%. Likewise, if the lateral length of the vent connector exceeded certain values, capacity must be reduced again.

Note only did Rhodes have to consider the effects of over 30 notes and exceptions on his designs, he had to constantly perform tedious interpolations on the values read from the tables. The tables necessarily cannot list every possible combination of vent height, lateral distance covered, and connector rise. Thus, it was common to land “in the gaps” of the tables. Rhodes would often have to decide whether to “eyeball” interpolate or perform the painful math of true interpolation. Rhodes was always having to avoid using guesswork in his designs.

Any changes brought up by the contractor just added that much more agony to the design process. Rhodes remembers, “Back then, we spent a lot time going through the tables and making sure we did everything just right. Last minute changes caused us to waste a lot of valuable time that we were never compensated for.”

In hopes of automating laborious vent design, Rhodes purchased Elite Software’s GasVent program for Windows in 1993. The program is available for both Windows and DOS, but he chose the Windows version for maximum ease of use. He also liked the fact that the program is based on the exact same tables that he had been using manually. In this way, he could easily check the program’s accuracy and have confidence in the results.

Rhodes soon discovered that a typical vent design could be done in minutes versus the hour he used to spend. Rhode notes, “To use GasVent, we only have to know the btuh rating of the equipment, type of vent system (tile lined masonry, single, or double wall), vent height, lateral distance, connector rise, and whether a fan assist or natural draft is used. We enter the information into the GasVent program and vent sizing results are displayed instantaneously. Changes and alternative scenarios can be evaluated in just minutes. The ability to enter our own equipment btuh ratings into GasVent’s equipment database also makes designs that much quicker.”

One recent job Rhodes worked on was a multi-story apartment complex with three furnaces. Rhodes states, “To size this job from the AGA manual might take over an hour, but with GasVent its done in fifteen minutes with great accuracy and a professional report. Before computerization, we would spend most of that time trying to make the job fit the tables. Multi-story vent systems are complex and working through the AGA manual for those situations is very time consuming. There are also more chances to make mistakes.”

Rhodes continues, “With GasVent, we can use exact figures, dimensions, materials and equipment ratings rather than trying to pigeon hole the design into a certain table. The program also guards you from impractical and unsafe designs. If you enter unreasonable data, the program will alert you to the unacceptable design.”

“With GasVent, we get precise, properly sized vents and connectors. We are also advised on the combustion air requirements for the given equipment and venting situation. This means that the customer’s equipment (furnace, water heater, stove, etc.) will operate at maximum efficiency and save them money. More importantly, we are able to offer the customer an exceptionally safe venting system.”

Rhodes adds that the program’s reports play an important role in creating customer confidence in the designs they recommend. Before GasVent, Rhodes would typically give customers a verbal report or maybe a handwritten note. Rhodes reflects, “It’s critical that the customer feel good about our designs. GasVent’s report’s are impressive, persuasive, and professional. The reports lists all input data as well as showing the minimum and maximum allowable sizes for all vents and connectors. It’s important that the customer have something in writing and a recommendation on paper. Our customers trust GasVent’s clean and credible reports. For Young Supply, customer trust means good customer service and more sales.”

Rhodes exclaims, “The speed of GasVent means that I can do three or four jobs in the same time I used to do one by hand from the manual. This is very important as our work is seasonal and a large percentage of our sales occur in a short period when we are very pressed for time. I also feel more confident with the results from GasVent as I believe there is less chance of making a mistake or forgetting about a sizing rule.”

Rhodes concludes, “These days, things are moving fast with everybody using computers. GasVent is not only fast computing, it’s also very easy to learn and use, much easier than learning the manual process. In our business, we have to size it right the first time every time. In the end, everybody wins. Our customers get fast, accurate results, and we save time and sell more equipment. Its a good program.”

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