Clamp-on BTU meter(Ultrasonic heat meters) are available

RBFM series Clamp-on Ultrasonic heat meter(BTU meters) are available.
RBFM Fixed Clamp-on ultrasonic heat meters (BTU Meters) employ the proven transit-time ultrasonic flow measurement technique combined with two PT 100 temperature sensors (or customer-supplied RTD sensors) for calculating total and instantaneous energy consumption. Flow measurement may be achieved via clamp-on, spool piece, or insertion-type sensors. Our microprocessor based, user friendly field programmable flow measurement technique creates no interruption of the process flow and allows for easy installation.

RBFM Fixed Clamp-on ultrasonic heat meters(BTU Meters) Features:

•  High accuracy - ±1% of reading
• Bi-directional flow measurement
• Wide range of fluid velocities - 0.03 ~ ± 105 feet/sec.
• Transducers for pipe sizes ranging from ½" to 240" (15 to 6000 mm)
• Measures energy consumption rate and total
• No moving parts,
• Fixed and Portable version
• Proven ultrasonic technology for flow measurement and PT 100 for temperature
• Clamp-on, spool piece or insertion mounting for flow measurement
• RS485 and Modbus communication protocols available
• 4-20mA and pulse outputs with available relays and alarms
• Data logger function - includes time & date, totalizer, diagnostics
• Fast response time - less than 1 second
• NIS
  
  http://www.rbflowmeters.com/Applicantion-HVAC/Clamp-on_Heat_Meters.htmlT traceable calibration certificate （optional）