As today's modern world looks to improve energy efficiency in appliances such as washing machines, furnaces and HVAC systems, new motor technologies have evolved. Some of these technologies utilize switched dc pulses. Although fast switching helps keep efficiency at its best, it can also increase the probability of an RFI problem. 

Unfortunately, these problems can be challenging to solve. Warrantee issues, for example, might require that an approved fix be installed by an approved service technician to an expensive new furnace or central air conditioning system. Even without warrantee issues, attempting to access a motor inside something such as a furnace or air handler is beyond what many hams might choose to attempt. 

While it’s always best to check for potential RFI issues before making a purchase or signing a contract, this doesn’t help in the event of a pre-existing problem. A good first step in this case is to check with the manufacturer or your contractor for technical support. A number of furnace manufacturers, for example, provide RFI kits for their products. After that, information on this web page will hopefully be of help.

• Resolving Furnace and A/C RFI (Radio Frequency Interference) Problems: Lessons Learned, by Roger Hillson, KM4LHZ.  A presentation for the Virginia Wireless Society.
  
• Ray Anderson has also put a Video of Roger Hillson's 35-Minute Oral & PPT Presentation given as a club talk.  (Please note that this version has subsequently been revised.  The latest PDF version is posted above.)
• August 2021 Zoom Presentation by Steve K9SAN and Roger KM4LHZ
• August 2021 PDF slide deck for the Zoom Presentation