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Posted by rick on March 27, 2005 at 16:06:39:
In Reply to: Re: Temp. overshoot posted by HeatPro on March 27, 2005 at 11:02:12:
: The gauges and the hottest water are often in different sections of the boiler while the boiler is running. Different flows can be in different sections of a boiler while the burner is on; but the water mixes when the circulator stops. This is often because the water flow is restricted to the rate of the tubing it is attached to. If the piping is changed to a loop-subloop configuration so the water flow in the boiler is at maximum no matter what the flow rate required for the radiation, the variation would most likely cease.
: The charm of cast-iron is that it 'holds heat' and it has a somewhat delayed transfer of heat that keeps the fire side hotter than the water side when the burner is on and the water flowing. This helps assure that the fireside remains above condensing temperature, as water on the fireside of exposed hot cast-iron will rust it severely. Stop the water flow and the higher fireside temperature is then transferred to the water side. Another possibility is to add a delay to the circulator control so it continues running for a minute or so after the fire dies so the fireside heat is absorbed and distributed through the system rather than heating the still water inside the boiler.
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Mr. Pro. you're right on because if indirect hot water tank calls for heat, since the pipe size going to it is identical to the pipe coming out of the boiler (1 inch), the temp variation is less than 10F whereas radiant Ipex tube is only 1/2 inch. And this overshoot happens with radiant heating, not so much in HDW heating.
but I don't know if I understand your circulator suggestion. I know my circulator is always on as long as there is a call for heat. Therefore, if there's a call for heat, the cirulator will stay on after the flame goes out which theoretically transfers and distributes the fireside water to mix with the not-so-hot water like you said. So, why is there the disparity in temp?