In the first three printings of "A Glassblower's Companion," on page 106, first paragraph, there was a numeric mistake. The text reads "The venturi mixer operates on low pressure propane (6" w. c. i.) with a #18 orifice." Please correct the text to read "with a #54 orifice." Subsequent versions of the first edition have been corrected to reflect values shown in the chart below.

That being said, I have published a free paper on the pipe warmer which is very much up to date which is made out of 1" square tubing rather than the round pipe. This design I first saw in the glass shop of Alex Kalish from Hillsborough, NH. He fed it with a small blower/mixer. After initial experimentation using the same hole pattern as I had originally placed in the round pipe design (35 holes at 3/16"), the square design worked great. For the mixer I used a Ransome V050B Venturi using the orifice scheme as shown below in chart.

Suggested Orifice Chart
Natural Gas 6" WC #48 Orifice
Low Pressure
8"11" WC #54 Orifice
High Pressure
1-2 psi
You will not need much pressure
Use needle valve to modulate gas flow
#65 Orifice

The orifice I have in my shop burner is a #65 and it works great. I find the square tubing works a lot better than the round pipe that I originally used in the pipe warmers I first made for Haystack School back in 1982