Posted by Harold Kestenholz - Hydronic Network on March 05, 2001 at 11:59:32:
In Reply to: General - Hot water heating system ? posted by Brian Fish on March 04, 2001 at 11:58:57:
Gravity systems were installed because electricity and dependable pumps were not available early in the last century. The water has been running around the system for nearly a century without a circulator. The problem is that a gravity system is not very fast. When the first boiler was installed, it burned wood and or coal all day and never had an off cycle, so there was not much heat-up time. You can change the heating pattern to the original by installing an indoor-outdoor control that will keep the water just warm enough to give off a constant and comfortable heat all the time. The cold weather outside does not go on and off with a switch, it changes gradually, so an indoor-outdoor reset control can follow the weather. In this way, you can get the system back to the original intent and not need a circulator because the radiator will not get cold until the system is shut down in late spring.
If you want to have a hot water system act as an on-off system like a warm air system, then you can add a circulator. This will not make the radiator warm up quickly unless your boiler is 3 times larger than you need it to be. Your boiler must heat itself up, plus 1 ton of pipe and radiators and another ton of water before the heat is at its necessary temperature for the radiators. As the water circulates by itself, you need only install the weakest circulator you can find to help it along. Put a big circulator in and your entire system will whiz cold water around until the boiler can heat up the tons of mass.
The many gallons of treated water inside your system a re pure gold because it is deoxygenated as much as possible. Draining the water out introduces air containing 15% oxygen to corrode the pipes and boiler more. Adding fresh water introduces 5% by volume of air in the water to corrode. Doing nothing but having the water checked for acidity level and treating it to neutral is the greatest help. Your local plumbing supply or county agricultural center can test the water Ph.
Corrosion on valves is a matter of time and exposure to the air and leaks. Prevent leaks and clean the valves to minimize corrosion.
You can find out more about hot water systems at http://www.hydronic.net