Water Side Scale

I don't know wheither general or broad statements would be of real benefit. But, IF the heat generating process and using process are constant, then an equalibrium would be reached between the two processes, and constant stack and water temperatures would result which could be an indication of the amount of scale. However, any variation in any condition of either process would result in variations in either or both the stack and water temperatures. I don't think is would work.

If the heat generating system is a closed system, such that the water is recirculated and reheated, and assuming a reasonablly tight piping system, once the water is neuturalized, you shouldn't have a scaling problem. This system could be tested when put into operation and the water would be treated, as required, to prevent scaling. Periodic testing then is all that is required to maintain proper condition of the water. A water meter installed in the makeup water line would provide a history of the amount of makeup as an indication of leaking or otherwise any loss of water.

If the system is an open or once through system, the water would be treated prior to entering the heating system. The size of the system or amount of water required would determine the type of treatment used to treat the water. There are several methods depending on the quality of the water. Major ones would include filtering, chemical, reverse osmosis and distillation. Several manufacturers provide relatively inexpensive instrumentation for record keeping and/or as controlling treatment.

Properly filtered feedwater low in organics? Low total dissolved solids [TDS] feedwater? pH around 8.5? Antiscalant and oxygen scavenging chemistry in use? Blowdown at around 2000ppm TDS? Regular visual inspections by an insurance inspector to look at the mechanical aspects of the boiler?

No. You need to install both a gas flow meter on the burner and a steam flow meter on the outlet main of the boiler. Both these will then indicate and monitor drop in efficiency which you can improve by tuning burners and cleaning tubes, insulating exposed surfaces etc., close monitoring and drop in efficiency will indicate propable scaling but not amount or quantity. Then Automatic Boiler blowdown system to be incorporated to minimize. But still quantity / amount cannot be indicated.