Arkansas HVACR NewsMagazine January 2024

HVACR NewsMagazine January 2024

Tech News

Troubleshooting 90%+ Gas Furnaces By Bryan Orr

furnaces in that they have a dedicated air intake, a primary and secondary heat exchanger, and a condensate assembly. We get more energy efficiency out of these furnaces because there is more heat transfer over a greater surface area, which we owe to the secondary heat exchanger. With that added efficiency, we get cooler flue gases and condensation; since water vapor is a byproduct of combustion, cooling it will cause it to condense into water. Water vapor changing state to a liquid releases many BTUs of latent heat energy. Condensation on an 80% furnace will eventually lead to corrosion because acidic flue gases are involved, but 90%+ furnaces manage condensate removal by design. As a result, 90%+ furnaces have unique troubleshooting challenges compared to less efficient appliances. When it comes to piping condensate assemblies, we must be mindful of where we direct the water. That water mixes with flue gases and will be acidic, so we must keep the water away from corrosive materials, including metal plumbing pipes, or use an acid neutralizing device. 90%+ furnaces typically use specialized PVC for condensate drainage for that reason. Inside the unit, our secondary heat exchangers are usually made of stainless steel to reduce corrosion, but they’re not immune to it. Pitching the furnace slightly forward can help keep acidic water from accumulating inside the furnace’s secondary h eat exchanger. Common Problems with Water Management

This tech tip recaps the livestream by the same name, featuring HVAC School contributors Matt Bruner and Adam Mufich and special guest Ty Branaman. You can watch that livestream on our YouTube channel HERE and visit Ty’s at https://www.youtube.com/@love2hvac. While 80% gas furnaces are relatively commonplace in the Southeastern United States, where HVAC School is based, 90%+ high-efficiency condensing furnaces are popular in more northern markets. 90%+ efficient furnaces have the fastest return on investment in the northern climate with longer heating seasons. They are also commonly used in well-sealed high performance homes, such as homes with spray-foamed attics. These high-efficiency furnaces differ from 80% induced-draft