Posted by Harold Kestenholz - Hydronic Network on December 26, 2000 at 17:43:46:
In Reply to: 1912, 6000 sq.ft in the South posted by Daniel on December 26, 2000 at 06:34:12:
If your system is a water system, not a steam system, when you close valves radiators upstairs, water will not be pumped upstairs. If your system is filled to the top, a pump is not required to pump water to the top, its only job is to circulate water through the system. So if you closed the valves to the radiators upstairs, and the pipes are getting warm, it is because you have gravity flow within the large vertical pipes, which happens in pipes 3/4-inch and larger.
If you want these pipes to be cool, then you will need to introduce valves in the basement to prevent all flow through the vertical supply pipes. You can zone by installing zone valves on each riser to the upstairs radiators. Unfortunately, zoning was not a concept in 1912, so the gravity systems installed then used two-pipe systems that ran risers to each radiator upstairs from the downstairs main. This means that even the warm water in the returns will make some gravity flow up and down within the return pipes when you put zone valves on the supplies.
You have choices:
1. Repipe the mains so there is a section of the house you want to heat from a smaller main and tubing - and the rest of the house on the remainder of the original main making the house a two-zone system.
2. Settle for the zone valves on the risers - then some heat will circulate within the radiator return risers.
3. Repipe the risers with 1/2-inch tubing run inside the existing risers using the risers as pipe chases so gravity flow will not occur to heat the riser pipes.
4. Leave the pipe alone and spend the money on insulating the building. This will give the greatest payback.