It seems like boilers, in a lot of cases, are not sized well to match their duty. 

We've been trying to look at data on heating systems, Load = GPM * DT, and then comparing that to monthly natural gas bill data. There seems to be a big gap between the design loads and the actual. Most importantly, the boiler systems spend a LOT of time at low loads (Where i think efficiency is pretty bad, and the data seems to back that up)