Posted by Harold Kestenholz - Hydronic Network on October 20, 2001 at 10:37:36:
In Reply to: Hot Water Radiators posted by Gerard Nardone on October 19, 2001 at 18:55:44:
Cast-iron radiators take a while to heat up because of the weight of the metal and the water inside that must be heated. They also take some time to cool down for the same reason. The benefit of cast-iron radiators was their 'swing-time' which meant that once they were heated, the circulator could be shut off and the radiators would continue to heat the rooms. This was a great benefit in 1920, when circulators would wear their seals out; todays residential circulators can run continuously without a problem.
A lightweight copper/aluminum fin baseboard contains about 1-1/2 pounds of water per foot and therefore does not retain heat. Copper-tube baseboard heats up fast and cools down fast, so a baseboard and a a cast-iron radiator on the same circuit, but in different rooms will heat the rooms differently. The baseboard room will overheat, then underheat, making the room swing in temnperature and the cast-iron room will remain a little cooler. However, baseboard and cast-iron radiators on different zones with separate controls will function well in a building.
All this is less of a problem when using cast-iron baseboard with cast-iron standing radiators on the same circuit. Although cast-iron baseboard can be ten or more times the cost of copper baseboard, it gives long-lasting comfort similar to the standing radiator, can withstand impact, and fits in about the same space as a copper-tube baseboard. Properly controlled with a bypass automatic radiator control, it will provide the comfort you are seeking with a low profile.