trane vapor system piping

Boiler replacement

What size system is this?

Generally the correctly-sized boiler will have enough water capacity to make steam capable of filling the entire system without running out of water. When new boilers run low on water while steaming, the cause is usually excessive steam pressure forcing water out of the boiler, up into the returns. A receiver/feed tank is just another unnecessary complication/hindrance to operation. Keep the pressure below 2 ounces (by correct sizing), and maximize the main venting so it is the equivalent of an open pipe.--NBC

Unless you *completely* understand that old system

you might want to raise the new boiler up so its waterline matches the old one.

Oh dear

You mention at one point that the new water line will be lower than the old one.



NO NO NO!!!!!



Match the new water line with the old one.  Otherwise, you will be in a world of hurt.  They do depend on the water line in the boiler being high enough so that all of all the wet returns are, in fact, wet -- that is, several inches below the lowest permitted static water line in the boiler.



As SWEI said, unless you take the time and trouble to completely understand how that system was intended to work, and you make the necessary piping changes to make it work with a lowered water line, don't lower the water line.  Just don't.



As to having enough volume of water in the boiler to fill the pipes with steam.... that's usually not a problem.  Consider that one cubic foot of water makes about 1,000 cubic feet of steam!  The most common reason that the water line drops as a boiler is steaming is not that the water boils away -- that might give you as much as an inch of drop, but not much more -- but that the pressure is too high, and the water itself is backed out of the boiler into the return piping.  Keep the pressure down.  The other reason is that the return piping is so crudded up that the condensate simply can't get back to the boiler in a reasonable  time.  The obvious solution to that is to clean -- or in an extreme case, replace -- the offending return.

Quite so

JStar is right; I'm just somewhat conservative!  If you go through the whole system and find every single place where a drip -- either from a steam line or a dry return -- comes into a wet return, and set your new water line at least a few inches above that, you'll be fine.  The trick is to find them all; even one will mess you up -- which is why I prefer setting the new boiler up on a pedestal (think of it this way -- you're paying enough for it, why not put it up where you can admire it?!).



Repiping is, of course, an option -- subject to the same comment on finding every single place where a drip comes in and making sure you are low enough.

you should be OK

If the level of the return piping after it drops down near the boiler, that part being the horizontal run where the check valves are located in the piping on either side of the Trane Direct Return, is near the floor, or at least well below the water line of the new boiler, you should have no problem.