to moniotor  the heat flow,u need 2 things.1-  a liquid  flow meter & 2-  a temp. tranimitter. And then  u need an indicator which will receive signals  from both flow meter and temp.trans.
 then it will calculate and display the heat flow rate.

 u have to install the flow meter and TT in the flow line.

 but this will b a costly one.

If you want something really simple you could turn into the calories meters that are used in homes to calculate the cost of central heating systems.
They essentially assume a constant flow rate (I don't know if this is your case, of course a circuit with constant configuration is required) and integrate the hot temperature over time, also assuming an essentially constant return temperature.
A more sophisticated type of meter includes a rotary meter and is hence capable of accounting for flow too.
This kind of meters are in the consumer market, so their cost shouldn't be very high, however they are normally limited to small flows (a few cubic meters per hour) and temperatures below 100°C.

prex

http://www.xcalcs.com
Online tools for structural design

CRG!

The meters are already available. The math, memory and metering is built into one. They are called BTU Meters. Check with Spirax Sarco Metering Division. (Krone, a subsidiary of Spirax manufactures these meters)Endres+Hauser also has these meters but computational part is given separately.

If you don't have a control system better go for those relatively expensive meters. Otherwise I would suggest using two temperature transmitters for inlet and outlet loop temperatures.

www.onicon.com
Clyde

A company we use for BTU Meters is ISTEC
Check them out at:
http://istec-corp.com/productstop.html