An installer sets up a zoned distribution system. To keep it simple, he uses the same size piping for the headers and all the distribution circuits. The heat source is a low-mass copper tube boiler with high flow resistance.
An installer who is used to boiler replacements may view the mechanical room aspects of changing from a boiler to a geothermal heat pump the same as a boiler changeout; just swapping out one “box” for another. Unfortunately, this can lead to some significant operating problems.