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Posted by HeatPro on October 19, 2005 at 16:50:00:
In Reply to: Split a whole house one Zone into 2 posted by WSteger on October 19, 2005 at 15:58:23:
An old gravity system was installed when the concept of zoning didn't exist. The wood or coal boiler that fed it was fired up in the fall and shut down in the spring with the fire made bigger or smaller according to the weather. In other words, it was meant to flow water all the time. The circulators were added later as a 'new thing' but were never really needed for a well-designed gravity system. Circulators called 'boosters' might have been added in poorly-designed ciruits.
In other words, the large amount of water in the system makes it a poorly controlled system to start and stop water after the heat is needed.
You would do better to use the system in the old uninsulated house in the manner it was designed and then consider changing it to a small-pipe on when you find you can no longer afford the pink elephant and insulate the house, cutting your fuel bill to 1/4 of what it uses.
Have the circulators wired to run the water constantly as the old gravity system did. Have a HeatManager from R.W. Beckett installed to control the burner along with the thermostat, so it will regulate the water temperature as needed. The cost is much less and comfort will improve.
You wouldn't want to wait an hour or so for heat to come up from activating a zone valve or starting a circulator to heat up all the water and radiators in the zone that was off on setback while the other zone dropped in temperature as the whole water content resettled down to the average and then came back up to temperature.
If you left the thermostats set at one temperature, there would be little difference with two zones compared to leaving it as is and doing as suggested about the circulator(s) and Heatmanager and the HeatManager will save you money.