Advantage:
High seasonal efficiency with outdoor reset control system that allows reduced boiler loop temperatures during milder weather.
Disadvantages:
Highest equipment cost.
Condensing cannot occur when boiler loop temperatures are above 130F, as is often the case when weather gets colder.
Advantage:
Lowest equipment cost.
Disadvantages:
Lower seasonal efficiency.
Limited ability to employ loop temperature reduction strategies such as outdoor reset
.
Combines condensing and non-condensing boilers to offer the fastest payback on investment in a conventional boiler heating system. System utilizes condensing boilers when moderate temperature allows for lower loop setting and condensing operation. System uses less expensive non-condensing boilers to supplement heat output on colder days when loop temperature is too high for condensing operation.
For a slightly more detailed and technical explanation, click here for a pdf document.