DIFFERENCES IN HYDRONIC SYSTEMS

Roy Rantilla

My old house and new house have similar hydronic heating systems, except:
1. Circulator in old house pumped out of the boiler, new one pumps into the boiler.
2. Circulator in old house ran whenever boiler water was above about 130 degrees, new runs only when thermostat calls for heat.
Is either right or wrong? What are advantages, disadvantages of each?

Paul Pollets

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Brad White

Distinctions and Differences

Chances are the old boiler was correctly piped, more specifically if it was pumping out of the boiler it may have also been piped downstream of the expansion tank connection point. That it was piped that way is not absolute but is more likely than what you have now, pumping into the boiler.

Always pump AWAY from the expansion tank. To do so will avoid air problems. Put another way, if you DO pump toward the expansion tank, you will likely create air problems, a cycle of venting and filling that cannot be a good thing.

Operationally, the answer is more complicated because there are issues of boiler protection involved. The 130 degrees is not arbitrary but a minimum setpoint for a HW boiler. Gas or oil should be kept in that range, with gas usually requiring a slightly higher temperature.

Operationally, you wind up firing your boiler yet not delivering the heat until the boiler is warmed, good and ready. Thermostat calls, boiler fires, aquastat makes contact and the circulator runs.

What you now have may well have the boiler maintained at temperature and the circulator can deliver immediately without a wait. But here you are keeping a hot boiler, perhaps.

Not a lot to go on, just some general principles that seem likely to me.