wet return question

Steve Nichols

Hi all,

I am in the process of getting bids to replace my old (circa 1930's) steam boiler.  The system is 1 pipe steam.  The wet returns are very long and have slight pitch to them as they travel across the front wall of the basement.  As they turn the corner and head towards the boiler, they pitch more steeply and then finally enter the bottom of the  boiler. One of the wet returns is positioned about 1' below the other and runs parallel to the other one.

This system is very old so no hartford loop, equalizer or such.  System has run fine, no banging, etc.

I have had two different opinions on the existing wet returns.

One contractor wants to repipe the wet returns and bring them down to floor level.  He was not happy with the current configuration.

The other contractor said there will be no problem and the location works in our favor.

I re-read a portion of one of Dan's books and this seems to be similar to an example he gave that produced negative results for the installer.  With the existing boiler, if you measure up 28" from gauge glass center, those wet returns are indeed wet; 95% of that piping is below that line.

If we go to a shorter boiler, over half of that "wet return" piping will be above the 28" measurement.  Will this cause banging upon startup?  Am I missing something here?  Both contractors are listed on this site, so I'm getting confused and a bit leery.  If pictures will help, I can post.

Thanks in advance.

Dave in QCA

28" is Dimension "A" for Steam Carrying Lines

Steve,  It sounds like you have a good project in your near future!

I think you are confusing something in reference to the 28" measurements.  Dimension A (28" above water line) states that all steam carrying pipes must be at least 28" above the water line in the boiler.  That has nothing to do with the level of Wet Returns.

A wet return MUST be below the water line of the boiler.  This means that all portions of the wet return must be below the water line.  Since the water line can fluctuate, having it several inches below the water line would be advisable.

The big question will be what is the water level of the new boiler compared to the old boiler.  if it is lower, and it probably is, then you need to get to work and measure the level of the wet returns to makes sure they are all below the water line.  If they are not, you might consider a different model boiler, or setting the new boiler up on blocks, or lowering the wet returns, or installing a false water line set up.

Hope this helps, and also if I have missed something, one of the Pros will jump in add to or correct what I have stated.

Steve Nichols

Wet returns definitely above water line

Thanks Dave.  I was under the impression that if the wet returns are above the boiler water line that they too become steam carrying pipes.  As it stands now the wet returns are mostly above the existing boiler water line.  They are pitched ever so slightly as noted in my first post.  These returns average at a good 4' above the ground for a good portion of their travel back to the boiler.I don't know how high the boiler would need to be placed to achieve the same result.  Maybe if I can get some dimensions on the new units I can figure this out.

I know people have said this before but here it goes..."well the system has run fine so far.. no banging, etc....so I'm at a loss as to why it has worked with the wet returns so high."

I am hoping that the cost to repipe the wet returns isn't too large b/c the cost is creeping ever higher...

Hap_Hazzard

What kind of shape are they in?

If the wet returns are about to rust through you're looking at re-piping in a few years anyway. They tend to rust through first at the threaded ends, where the pipe is thinnest.

nicholas bonham-carter

High returns

If your pressure is high enough, the return water level is probably rising due to boiler pressure, and making the needed water-seal to keep steam out. If the pipes are in good enough condition, you could find an upstream joint, to make a vertical drop to the floor, and reuse the dry sloping return as a new wet return. Dry returns are frequently pretty clean inside, and may be good for another 20 years. Put in some flushing valves at the boiler end to keep them free from rust particles.

Make sure you get a good low-pressure gauge (0-3 psi)on your new boiler, and enough main vents to keep the venting back-pressure below 2 ounces.--NBC

Steve Nichols

Wet Returns, the saga continues

Hap and NBC, thanks for the input.

Hap: The wet returns are in good shape from what I can see. 

NBC: Boiler pressure when running never goes above 1.5psi.  I think I understand about dropping the lines down to ground level and reusing the piping, but I guess my question still focuses on with the way new boilers function (sensitive to water level, much less water within the boiler, etc.) should these returns get dropped below the new boiler water level to avoid problems?

And...as a follow up, if a wet return is defined as return piping below water line, how much piping is necessary for these new boilers or is that not an issue?  I have about 15' of return piping that is below the current water line and about 25' above. 

Would a false water line work in this case as was suggested and do most steam professionals know how to do this?

I'm not at all against repiping to accomodate the new boiler but I want to make sure I understand what is needed since I am getting conflicting views from contractors currently placing estimates on the job.   The old boiler will be removed and abated first week of september so I'm trying to tie up all the loose ends.

Sorry for all the questions, I want to do this boiler replacement once and have it be correct.  Thanks for all the help you folks offer.

 

MikeyB

Pictures

Steve. post some pictures of the existing system, boiler, boiler water line, return lines, dry/wet, and see what the guys have to say

Steve Nichols

1 pipe steam system pictures

Good Idea MikeyB,

Attached you will find 5 pictures. 

The first should show the location of the returns relative to the steam line supplying the front of the house.

The second should show the returns "rounding the corner" and increasing pitch as they approach the boiler.

The third should show the returns drop close to ground level and enter boiler.

The 4th shows the water line relative to the wet returns shown in the background.  I know that the perspective is a bit off.

The 5th shows all elements together, the two main steam lines, the returns and the gauge glass. 

Fire away with questions/suggestions if you have them.  She's a beauty of a system, eh?



Steve

Dave in QCA

Veddddy Intahresting! --Arte Johnson.

As an owner of a system that has many major installation errors, but still seems to work reasonably well and quietly, I find your system equally interesting.



If you look at The lost Art of Steam Heating, you will find tables that will indicate what size dry returns and wet returns should be based on the EDR that they are serving.  Your lines look at least one size too small.  However, the installer appears to have attempted to compensate for that by adding unusual amounts slope.  So.... do you have wet returns or dry returns?  They are dry returns, except that the last portions of the lines are too low. They should travel at the recommended rate of fall until getting to the boiler, and then drop vertically down to well below the water level.  The horizontal portions of the piping should be no lower than 28" above the boiler water line.  The other option option would be to drop straight down at the end of your steam mains and run them back as wet returns.



The question remains as to why your returns are not banging up a storm.  It appears to me that your main vents are probably located at the end of the main near the point that the drip line drops into the dry return.  If that is the case, it leaves the return line un-vented, which is OK.  We all know that steam cannot travel into a pipe, radiator, or whatever, unless the air can get out.  If your dry returns are not vented, the steam can't get in, and thus there is no banging.  I would certainly expect, in spite of the slope of your returns, if steam was to get into them they would probably bang a bit, mainly because of the small diameter combined with the amount of condensate traveling in the line as well.



What works well with your old boiler may suddenly change when you install a new boiler with higher exit velocities and a different water level.  If it were my system, I would re-pipe your returns.  Wet returns are notorious for filling up with sludge so I think I would opt for dry returns.  However, I would increase the pipe size to correspond with the recommendations in the tables in TLAOSH.  I would keep the main vents at the end of the steam main, assuming that you already have vents at this location. If not, I would install them at that location.  I would leave the dry return unvented and then there is not much need to insulate it.  When the lines come around to the boiler, they should drop to well below the water line before they tie together, then they should rise up and connect to your new equalizer line in a manner to form a proper Hartford loop.



You're gonna love your new boiler!

Steve Nichols

mains are vented

HI Dave,

You are correct, sir!  The two steam mains are vented as you describe, just before they turn into the returns.  It would make sense now that with no venting after this, the steam would have a difficult time getting into them, thus no water hammer.  I'll go back and revisit the wet return pipe dimensions based on the EDR for each pipe. 

If as you suggest, I opt for dry returns, are you saying that they should be at least 28" above water line, then before entering boiler, drop down? 

JStar

My opinion

I would favor a dry return over a wet return, whenever possible. I've noticed that a return like yours, with so much pitch toward the boiler, does not cause as many issues as you would think, as long as the return drops fully below the water line. It's the truly horizontal pipes that may be a concern.



You could always fix the piping after the new boiler is installed. See how it reacts, and gauge its priority.

Steve Nichols

that may be a good option

Thanks Jstar for providing that information.  I just got a quote for repiping the returns down to the floor and it's a budget buster for me. 

If the new system works fine with the existing return piping, that would be great.  That is what I am hoping for and somewhat what I am paying for (good results).

The option for repiping later is something that I didn't consider.  

I guess at some point, I need to trust that the individual doing the work will do it right and deliver the expected results as I'm not a specialist, just a curious and concerned homeowner who likes steam heat.

JStar

...

I would at least drop the end of the return down to the floor before rising up into the Hartford Loop/equalizer. That should be easy, because you'll need to cut those pipes anyway to remove the old boiler.

Dave in QCA

exactly

Yes, that is what I meant to say.  Even though you may not be getting steam into those returns, it could be possible.  Any steam carrying pipe should be at least 28" above the boiler water line.

Also, check the pipe sizes and see if they are adequate.  If they are smaller than they should be, it may be working because of the steep pitch of the pipes.  If you raise the low end and decrease the pitch, it may cause a problem if the pipes are undersized.

As mentioned, you could leave the return piping alone and see if it works.  Of course, it needs to drop down low at the boiler, then tie together, then come back up to the new hartford connection.

nicholas bonham-carter

Do it yourself?

Would you consider a little piping project yourself?

The 2 dry returns could be dropped down into 1 bigger wet return which then goes back to the boiler. Use plenty of venting at the drop-down point, and keep the pressure low, so as not to prevent the condensate from getting home to the boiler.

Your installer could work with you on this, cutting the final short nipples to fit, while you do the initial pipe assembly. Put the pipe on bricks instead of directly on the floor, and don't forget the flushing/draing valve at the Hartford loop end!--NBC

Steve Nichols

always willing to work!

NBC, thanks for that idea.  I'm very handy and am sure I can tackle something like this.  Ultimately this will depend on the willingness of the professional who gets the job.

BobC

One more thing

A modern steam boiler is going to produce steam a lot faster than a converted coal boiler that is 80 years old.



I think that means you have to be careful to keep a dry return's A dimension in mind and may have to drop down below the waterline earlier especially if the slope gets very shallow towards the end. From what I've read on this board it takes a lot of experience to know what will work (that i don't have) and what might cause problems. Make sure you build in the ability to flush out whatever wet return you end up with.



Bob

nicholas bonham-carter

Do it yourself wet return

In my case, our contractor supplied the 2 in. Pipe, and I laid out the pieces, and threaded them together with unions, leaving the pro's to cut and thread the final short lengths, in the connections to the dry returns. I was able to do this pre-assembly before the old connections were cut off at the old joints (removing the thin circles of threads in the tappings).

This enabled the new wet return to be connected in one day to 6 dry returns. It was done in early February, when the temperature outside was 10 degrees, at 4am, I cranked up the heat for an hour, and then with my helper, cut the old pipes out of the way, before the pro's arrival. What a difference it made to have the wet returns finally piped as they should have been in 1952! I laid my new pipes on bricks on the floor so they would have some air circulation.--NBC