trane vapor system piping

Flip

need to install a new boiler to replace one around 80 yrs old.wondering about the return piping.really what to do with the return trap , check valves etc. also thoughts on the need for a reciever/makeup tank.

nicholas bonham-carter

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

Flip

vapor system

calculated 470sq.ft of radiators.came up with the need for 113k boiler. two pipe system. assuming the new boiler will be much smaller and should make steam much faster don't want to run out of water before condensate makes up. the house is about 2200sq.ft. two story.also one of my concerns is the return piping as far as keeping the return trap and associated check valves etc. the water line of the new boiler will be lower than the exsisting one.will havw plenty of highth for the A deminsion.will use a vapor stat on new unit.

SWEI

Unless you *completely* understand that old system

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

JStar

Trane

You can keep the return trap and return piping. Here's an example of a boiler we replaced on an old Trane system.



http://www.heatinghelp.com/forum-thread/144681/Job-Pictures-1930s-TRANE-Vapor-system

Jamie Hall

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.

Flip

pics

that is the same piping at the return to my boiler. thanks for the pics . BTW good job on that change out. looks like I should be able to use the pics as a guide. still have concerns about the new boiler water line matching the old. the existing boiler sits in a pit aprox. 1ft deep finished concrete which makes the existing water line about 18" to 24" above finished floor so this old boiler holds a fair amount of water which is why I am concerned about the new boiler running low on water before the system stabilizes and there is enough return to maintain water level. thinking of filling the pit in after old boiler is removed but the new water line will still be below the old one guessing by about a foot. maybe that's not a problem though?

Your Thoughts?

Flip

vapor system

Mr. Hall  ty for the come back. I guess a little back ground is in order. Have been in the HVAC/R ind.  for 30yrs. mostly service though. Have not been involved in a change out of  steam systems but after reading The Lost Art I'm sure I've seen many after the fact done wrong. This job is in a duplex we own and reside in that has two identical systems in it we want to change the older boiler out to get something more efficient.

Any way after all that being said I do have some working knowledge of steam and this system BUT would be a fool not to add that I learn something almost everyday.

Don't have the exact measurements but to match water lines on the boilers I'm thinking I would have to build up quite a base for the new one to sit on.

I do have access to all the equipment needed for repiping should that be a better option.

Your thoughts?  and thanks again.

JStar

Water line

As long as all of the returns stay wet, and don't leave a chance of mixing steam and condensate in a horizontal pipe, you should be okay.

Jamie Hall

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.

Flip

trane vapor

all returns come in high above the boiler then drop down at the boiler.

Dave in QCA

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.