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What book to buy, or other sources of wisdom

I have a rather large hydronic system in a 4500 square foot Victorian house. It was installed as gravity feed and the pipes maintain a seemingly consistent cross sectional area. Long ago it was converted to a circulatory system and about four years ago I replaced the old boiler with a new mid efficiency unit which was replaced under warranty when it burned through the case and caught fire. The heat loss calculations on the building were about 90,000 BTU. I am an electrical engineer and felt compelled to do the calculations my self and they agreed with the HVAC company with in a few BTU.

I would like to replace the large pipes that drape across my basement with something a little more reasonably sized, say 1", either copper or PEX. There are about 21-22 radiators in the house spread across three floors. If I change the water resistance of the system I assume I need to look at changing the pressure capacity of the circulator to maintain the required hot water flow through the system.

Do any of "Dan's Books" have the required information to not screw this up?

If not, is anyone aware of an on-line site that might have the required info?




  • Dan's book "How Come" will help you understand how the system worked under gravity and why the pipes are so large. It will also give you an idea of what's going on once the system was changed to forced circulation.

    If you really want to make the sort of changes you describe, I would suggest a completely modern book like "Modern Hydronic Heating" by Siegenthaler.

    Be forewarned that making such modifications is far from simple or easy. If you just reduce the size of the mains without resizing ALL of the branches appropriately for forced circulation you will absolutely screw up your system. Any semblance of balance will be gone and some areas may not receive any circulation.

    An alternative to this is "home runs" for supply and return to EACH radiator. These will connect to mainfold(s). In a house of the size you describe, multiple manifold locations may be greatly preferable to one near the boiler.

    Another alternative (what I did in my house) is to relocate branch lines (using the SAME SIZE PIPE) up into joist cavities as much as possible. While not utterly required, it's a good idea to use considerate plumbing when doing this such that everything still drains back naturally to the boiler and that you create no up-and-down "air traps" to cause problems when filling. By doing this only my mains are now hanging low and nearly everywhere else I have the full ceiling height. Since mains travel parallel and quite close together, they're usually not too problematic.
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