heaterman said:
Gooserider said:
I don't see why... I can't think of any real advantage to running a closed system over an open one as long as the column is over about 25 feet or so, in order to get a boiler pressure in the 12-15 psi range (FWIW, I think I can get 30' in our house) a properly set up column should have very little evaporation, or heat transfer into the top expansion tank.
I'm also not sure that a savvy inspector would let you get away with it... There are a few differences in the setup that would make it obvious that you were trying to pull a fast one - a Euro-column setup does not need or have a use for, a conventional bladder expansion tank in the system, but an expansion tank is vital in a closed system - seeing a bladder tank would be a real red flag that something was odd. Also I would imagine that code would get very sticky about having valves in the line that would allow shutting off the column line to the tank. While in theory it shouldn't matter where in the system one tied into the column line, I suspect that code would require that line to be a direct run to the boiler room and be difficult, if not impossible to shut off w/o disabling the system... I'm not a code guy, but to me it's a pretty obvious thing to require...
Gooserider
The only real pain I see is the amount of overflow you'd need in an open system with 1,000+ gallons of storage. You'd need something like 40 gallons of acceptance at the top of your 33' line to run 14psi and 1,000 gallons of storage.
Mt suggestion was more of a joke...but if someone were to do it they would obvioulsy have to make the modifications after inspection, not before....
I very seriously considered trying to do a Euro-type "vertical column" system rather than a bladder tank- both when I was still thinking of pressurized storage (I have the same problem as others of no way to shoehorn propane tanks into my cellar), and even for the boiler-side of the heat exchanger after I opted to go with un-pressurized storage. The couple of things I saw as drawbacks on the "vented tank with a vent way up, using weight of the water" were (1) needing to make sure that wherever the expansion tank would be located would be strong enough to carry the weight of the water; (2) making sure that the same spot would not be potentially prone to freezing if it was above or outside of (attic, etc.) finished/ heated space. For those who have ways around those constraints, great. One other factor- even though the "semi open" elevated expansion tank system is apparently common in Europe, I have to wonder if (a) all inspectors would understand it; and (b) whether a boiler manufacturer or importer would have heartburn over such a "semi-open to atmophere" system if the owner happened to have some problem with leaks, corrosion, etc.
In the end, for me, it was simplest to put a modest sized expansion tank in my primary loop on the boiler/ pressurized side of my system.
