jeffab

The run from the underground pipe to the heater is about 4 feet.

I am using 3/4" from the underground connedction. The pipe is buried to the meter so I can't tell you how big that is but I can tell you this is a replacement heater and my previous heater (not Raypak) did not whistle. The meter is a standard household meter (not an expert here). The whistling starts when the heater fires and doesn't stop until the heater shuts off (reaches temp).

I had a PM266a heater installed in May that has emitted a whistling noise ever since. Numerous phone calls top Raypak, my installer, and a local service company have not yielded any results except that the local service company made it clear that this is an issue with their heaters. It is annoying and I wish I knew this before I bought it