Water Hammer in Weil McClain Steam Boiler

MRC

Working at a home in St. Louis on Friday that has two Weil McClain EG-40 boilers installed. One for second floor and one for first floor. The original call came in due to water leaking from under the boiler serving the first floor. I found a boiler section leaking from years of rusting.
The topic changed to the second floor boiler. In 2012 the homeowners had installed a Fujitsu Mini Split with four heads. At first I assumed it was for cooling only and the boiler was still being used. They purchased the home a few years prior to installing the mini split. The homeowner said they used the boiler for some time but the water hammer just got to be too much and that is why they installed a heat pump mini split. The boiler has not been used for two seasons. It is a one pipe, parallel flow system. I asked the Homeowner if he remembers at what point in the cycle the wh occurred. He remembers it being during the beginning of the cycle.
I checked the hangars on the main. They did not seem to have come loose causing sags. With a level and tape measure, measuring from the subfloor, I checked down the mains at intervals of approx 10'. I found drops of 1/2" approx at these points. I say approx because I was measuring to the insulation on the pipes. The riser off the boiler goes straight up to an elbow. The total rise above the water line is approx 3-4' before entering the first elbow. The main then travels 8' then another elbow where it starts its trip around the basement. It is this 8' section that I suspect. It is virtually level its entire length from ell to ell. I am suspecting that there is condensate on start up being picked up by steam and slammed into that second 90 degree elbow. When I mentioned this to the homeowner he somehow remembers the hammer coming from the dry return that is less than 8" away from the steam main that is level. I am thinking that he is actually hearing the hammer in the main. I have not heard the hammer since the boiler is not operating at this time. Also, there is 4A quick vent on the return just before it drops down to the boiler. There is discoloration on the subfloor where steam has been shooting out of the vent. The homeowner said he thought this was normal. I have posted some pictures if anyone cares to comment on them. I am putting on a new vent and am recommending that downward pitch be added to the 8' section by installing a longer 2" nipple in the main riser off the boiler.
I have also included a picture of the return piping near the boiler. I believe the return drop should drop lower and then up to create the Hartford Loop.
Any help the Forum can provide is, as always, greatly appreciated. Also your patience with a "student"!

Mike Curran
St. Louis

MRC

Sorry Forum! Here are the pictures.

Mike Curran

Fred

From what I can see, The near boiler piping is all wrong. There is no Header and it looks like the eaualizer (what is suppose to be an equalizer is piped off the side of the riser. It should be piped off of the end of the missing header. How many mains are there? They should each be tied into the header, not elbowed off of the riser. Is the Hartford loop a couple inches below the boiler normal water line?
Looks like the only thing done right on that install was the use of threaded black pipe. Have them look at the owner's manual or pull one down off the internet and take a look at how it should be piped.

EDIT: Are the wet returns below the water line?

nicholas bonham-carter

The supplies, and Hartford loop definitely need to be changed to the Mfg's specs. Probably there is very wet steam traveling up, and causing much of the hammering. Do that first, and then see if any pipes need to be repitched secondly.
You may find that one boiler can handle the job of the two floors, as each boiler may be oversized, but add up the EDR of the rads to be sure.--NBC

Fred

Actually there isn't even a Hartford loop there. It looks like a dry return is tied into what is suppose to be the equalizer. Where is the wet return(s) tied into the boiler? That Dry return should drop down to the wet return, below the water line and then the wet return is carried up to become your Hartford loop in the equalizer.
EDIT: That is probably the source of the water hammer. When the boiler is running, if the water level in the boiler drops enough for the dry return to be exposed to steam, that steam collides with return water in the dry return and causes the hammer. The HO is probably correct that he hears the hammer in the return pipe.

nicholas bonham-carter

Once again, good call Fred. It's amazing the oversights of these installers from even somewhat long ago!
It's not necessarily a matter of "you can't fix stupid", but more likely the newest of their techs was sent out to do do a seemingly less important residential job.--NBC

MRC

Fred, I believe this boiler had to hammer from the day it was installed. That is a dry return that 90's into what someone thought was a Hartford Loop. Looks like I some work to do there! But something tells me the homeowner is going to give up on the steam system and just continue heating with the mini splits.
Thanks everyone for your wise counsel!

Mike

icesailor

Which would be a shame. Because there is no Mini-Split that can equal the comfort of a hydronic system. Steam or Hot Water.

Fred

I hope you can convince them to keep the steam. Once you make the needed fixes and do 2 or 3 skims (which you should eirther plan for in your cost estimate or show them how to do it) i am sure that system will make them very happy. I just hope sitting there for a couple years with the water at the waterline that it hasn't created some rot at that line.

ChrisJ

I'm curious the cost difference to run minisplits vs steam on natural gas.

Not including the cost to replace the equipment after it fails, which will add up as well.


Mike Curran, from a homeowner, thank you for being a true HVAC professional that takes the time to figure out how to do things right.

SWEI

ChrisJ said:

I'm curious the cost difference to run minisplits vs steam on natural gas.

That depends (rather dramatically) on COP, which in turn depends on the outdoor temp at the time you measure it and the design of the specific heatpump. Given current NG price trends, the crossover point is higher than it was a few months ago.