Forced hot water

Old 10-31-05, 08:02 PM
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Forced hot water

I have a forced hot water with big cast iron radiators. I am considering adding glycol to prevent freezing and augmenting the control system to have a delay to turn the circulating pump on and off. Right now the thermostat pulls in a relay and the circulator pump and ignition start at the same time. I am thinking that if I delay the pump for about 5-10 minnutes so the [pump is not circulating cold water. I also think that if I were to delay the shutoff of the pump so that it would run for a little while, I could effectively lower the thermostat and still be comfortable. That way I am not losing heat under the house. Will this work, if not what can I do to make my system more economical?
Old 11-04-05, 06:56 PM
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To begin with, you need to circulate water through the boiler when it is running or it will go off on high limit. That is why the pump comes on when the boiler fires up. In addition, if the water in the boiler is not circulating, you could create hot spots which would prematurely cause failure to the water jacket.

With regard to the pump continuing to run after the boiler shuts off, you could install a aqua stat on the system wired to the pump to keep it running until the temp drops to the desired temperature.

This would have to be installed by a plumber or heating contractor for it to be installed properly.

Old 11-05-05, 05:51 PM
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You do not have to circulate water any time the burner is firing. Any boiler with a domestic coil often fires without the circulator being on.
Old 11-06-05, 06:06 AM
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You will find better comfort if you circulate water anytime the thermostat calls for heat and let the boiler heat up gradually. It lets all the radiators get some heat and they can gradually get as warm as they need to be until the thermostat shuts the system off. The boiler is most efficient when the water in it is cooler. A post-purge would be good as long as it did not drive the room temp over the setpoint. If your boiler holds a lot of water, overshoot could be a problem. Instead of home brewing something, perhaps you could find an outdoor reset control that would achieve the desired result in a tried-and-true package. would be a place to start looking.


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