Odd Steam coil piping….help

Onepipe

So I will be replacing a boiler in the next week and while I was waiting on the new boiler to be delivered I wanted to get some work done at the house to save time on the job. (please ignore the reduced and bull headed header…..that’s going)Most of the main vents and rad vents were failed so I went around and replaced all the vents, increased some main vent sizes, flushed the boiler and put in some 8way to try and clean as much of the sludge out of the system prior to the new boiler and that’s where I came across this steam coil.

problem: (see pic) the coil is piped to the top off the main and the return comes off the bottom. The return is dry and is 30” above the boiler water line. There is a functioning check valve in the return line and a MoM with a #5 vent in it (vertical 3/8” pipe in the pic next to the coil) on a call for heat the coil heats up, the vent closes and the fan turns on, then when the boiler reaches about a 1lb of pressure (roughly 20 min run time) the vent opens up and spits water.
I am wondering if the check valve is holding back condensate wile backed by the operating pressure from the drop the the wet return and when the fan coil cools and allows the vent to open the 3/8” pipe supplying the vent is partly or all the way full of water is blasted sky high. I was thinking about removing the check valve with the new install and installing a smaller rad vent. 

Any thoughts would be appreciated. Boiler operating pressure is between 1/2 to 1 1/2”lb steam. New boiler will have a vapor stat with between 4 and 6oz. Boiler seems to be correctly sized to the house based on EDR and heat cycle is about 20 min and rarely hits max operating pressure. 

clammy

Is your condensate from that coil tied into the wet return not a dry and does it have a water seal . I would get rid of that check valve . Most coils on a single pipe system are bottom feed and use a non freeze tube in tube coil construction w a air vent and vacuume breaker installed on the top usually feeding top and return bottom requires a trap or a water seal . You could build a deep water seal and have your vent before the water seal and drop down and pop up into the bottom of your dry return . Remember to make your water seal deep enough to handle the pressure your running a 36 inch to 42 inch seal should be more then enough being your using a vapor stat . I believe I would go w the water seal over direct pipe into the wet return . Peace and good luck clammy

Mad Dog_2

Agreed Mad Dog 🐕 

Onepipe

@clammy , thanks for the info. So just so I am understanding correctly. Th e preferred location for the air vent with vaccum breaker is on top of the unit.

second. The preferred way to pipe it is rather than direct into the wet return, I would drop down to the floor and then rise back up a min of 36” (creating a water trap) and then take a dry return back to my wet return for the boiler?

Please see the drawings below that show both the existing pipping and my interpretation of what you are recommending.

questions: do you have a recommended type of airvent with a vacuum breaker? Will my MoM work?

can I keep both my supply pipe and return water seal loop all 1 1/2” pipe or do I need to reduce my dry return to 1 1/4” until I get to the wet return?

lastly, I’m assuming that I would want to pipe in a clean out drain at the bottom of that water seal trap but it can’t tie into the mud leg of the wet return right? I must keep it separate until I rise above the 36”
 

Onepipe

Also just cuz I the type of person the will go crazy not knowing why something is not working. Was I correct in my thinking that the current way it is piped, the check is holding back the condensate and when the coil cools and calls for more steam the puddles condensate is being pushed up into the now open airvent? Thanks for all the help and happy thanksgiving. 

dabrakeman

@Onepipe Sorry to sidetrack here but I was curious how you obtained the EDR for the steam coil in your boiler sizing? I am trying to do the same but not sure how to approach it.

clammy

If you bottom feed it just run your feed straight down into the wet return no loop seal and have a tee on the vertical drop below your coil inlet and pipe it from the tee to the inlet of having it pitched of course . You should be alright w just an air vent in the top unless heating outdoor air .
Peace and good luck clammy

Onepipe

@clammy thanks. Is there a preferred way to position the tee under the coil? See pic? I could bull head it ( option 1) or supply off the branch (option 2). Also should all the piping be the same size from the main take off to the wet return? Or should any pipe be increased/reduced. I plan on supplying it with either 1 1/4” or 1 1/2”. 

Thanks

Onepipe

@dabrakeman so I scoured the internet and information that I had and I could not find any information on the specific steam coil that I had. So…..what I did is calculate all the EDR for all other radiators in the building and then looked at boiler sizes. My EDR fell between two sizes so I chose the larger boiler size. I am assuming it’s adding roughly 10,000btu to the system. That guess is from experience but like I said earlier it’s just a best judgment. Hope that helps.

clammy

I would avoid that horizontal piping on the supply I prefer ,Just dropping straight down w the supply into your wet return . Cut in a tee and Use 2 elbows to connect bottom of the coil so as to get pitch back to the supply drop ,this way your condensate from the coil will flow back counter flow to the supply run out and back to the drop n into the wet return . This way should get some fairly dry steam to your coil w all condensate in the supply piping dripping into your return limiting any real carry over . I de put a union on the steam coil outlet . As I call it a over head drop or a nipple straight up and double 90 then facing down this alone will limit most condensate carry over it’s my preferred way to feed a counter flow system w the mains just extending and getting a 90 facing down fro the condensate . Just a little trick in my Felix the cat bag .
Hope that help peace and good luck clammy