Without a doubt the most common problem we see today
is the over sizing of the boiler, in all types of hydronic heating systems.

    Several things have contributed to this problem. First is that insulation and construction values have changed dramatically in the last fifteen years. Heat loss requirements have went from an average of thirty five Btu. per square foot to less than fifteen Btu. per square foot. This has taken heat loss requirements for a three thousand sq. ft. house from  over one hundred thousand Btu. to less than fifty thousand Btu.
    Second is the fact that boilers have increased in efficiency from about seventy five percent to eighty five percent. 
    Third is that boiler construction has changed, today's boilers weigh about one half to one third of what they did twenty years ago. This contributes to higher fire side temperatures, and a lower boiler mass to absorb thermal shocks, leading to a shortened boiler life.
     Fourth is the reduced amount of water in the boiler, many of today's boilers hold less than five gallons, often boiler cycles are reduced to three or four minutes, this can reduce efficiency to less than fifty percent. Installing a primary boiler loop with a secondary heating loop will not increase the boiler volume appreciably. Most radiant heating systems require less than two gallons per minute if only one zone is calling for heat.
     Last and not least is the nature of the average plumber, who like all of us, if he has not run an actual heat loss on the structure, wants to make sure he is not under sizing the system. With increasing house sizes, shrinking boiler sizes and shrinking heat loss requirements, it is nearly impossible to guess the proper size of boiler.
    With most residential new construction, sizing the boiler at twenty Btu's per sq. ft. of heated space is more than adequate, many of the more advanced construction methods are realizing heatloss under 10 Btu's per Sq. Ft..
     Combo systems that hold twenty or more gallons of water are immune to these problems and over sizing has no effect on the efficiency or life of the heater.
     All radiant systems should use a modulating boiler or a tank type heater.