Does a Two Pipe System Need an Air Vent in the Dry Return?

JRice2010

Hi, I just had a steam boiler replacement in my parents house.  The system is a two pipe radiator system with two loops.  One short loop feeds the front of the house and a second longer loop feeds the rear of the house.  The house is a fairly large three floor house with 17 radiators.  None of the radiators have steam traps on their return line. I also have seen no evidence of any F&T traps in the system.  But what are system always did have where air vents.  Two air vents where in the  long front loop main supply and one vent was on the end of the dry return.  The installer of the new system removed all the vents, which I believe were Hoffman 75, and replaced them with vacuum breakers.  Before this work was done, the radiators in the front of the house, served by the short loop, always got hot the quickest and fully.  Some radiators on the back loop didn't get fully hot.  Now the rear loop radiators get fully hot, if the system is turned up fairly high and runs a long time, but the front radiators never get fully hot.  Whet the system is set to a reasonable temp, 70 degree, the system cycles through so fast that most radiators only slightly get warm before the system shut off.  I questioned the installer about why he removed the vents and his response was that two pipe systems didn't need air vents and that he put the vacuum breakers in to relieve the vacuum in the line and allow condensate to return to the system faster.  To me it seems that he is allowing air into the system without any type of exit.

Charlie from wmass

If air can not get out

then steam cannot get in. Not exactly expert steam installation. YES you need those vents! Not all two pipe systems used traps. some used orifices, others used steam vents. Since it is Sunday I am just giving a quick reply, I will look closer at the photos you attached.

BobC

Venting

I agree you need air vents for that system to work correctly. The question is weather the Hoffman 75's are large enough. How long are the mains and what size pipe are they (outside circumference will do)? How long are the returns and what size pipe are they?



The header and mains should be insulated for best performance. It will make the cellar colder but will save fuel.



Bob

Dave in QCA

No vents on radiators, system vents still needed

For a system with absolutly no venting, your's is doing exactly what would be expected.  The little steam that is making its way up part in the system is probably due to some air venting that might be occuring around loose valve stems.

Your contractor probably read that vents are not needed on a 2 pipe system, that is to say, vents on the radiators.  That's becuase the venting of the radiator takes place by air being pushed out through the trap, orafice, or whatever device your system is set up with.  However, in order for the air to be able to be pushed out of the radiators an into the return piping, there has to be a way for that air to escape.  That is what the vents in the return mains were for.  And as for vacuum relief when the system shuts off, they perform that job too.

End of the steam main vents are necessary to allow the steam to run to the end of the main before entering the radiators nearest to the boiler.  If you don't have them, the system is very likely to heat unevenley, with some radiators getting much hotter than others.

I would suggest that you purchase the book availabe on this website, entitled, The Lost Art of Steam Heating.  It is obvious that your contractor needs a copy too!



I would also point out that the near boiler piping looks a little "iffy" too.

Rod

You need Main Vents

Hi - If there isn't a trap on the ends of the mains, they usually are piped into the wet return and have a large capacity vent (Main vent) at the end of the main to let the air out so the steam can take its place. There also has to be a large capacity vent on the dry return which has the exit pipes from the radiators connected to it, for the same reason to allow the air to escape so that steam can move into the radiators. These main vents will release air but close when hot steam reaches them. When the burner in the boiler is shut off and the pipes and vents cool, the main vents open and allow air back into the mains. Where your installer came up with this vacuum breaker concept I haven't clue. As this system is a orifice system, it runs on very low pressure, normally ounces rather than pounds of PSI.

At what steam pressure does you system now run?



As for the boiler piping - You need to look at your boiler's I&O manual (Installation & Operation) as it should show the recommended piping configuration and sizing for your boiler. I think you'll have a hard time matching the drawing to the piping configuration you now have. Charlie is an expert steam pro and can possibly give you a better idea of what sort of performance to expect from your system as it is now piped.

As there appear many irregularities with this installation, I'd go back to square one and check every step out. How did the installer decide on the size of the replacement boiler?

He should have measured all your radiators and determined their EDR then computed the size of boiler required. Have you seen these figures?

Here's a couple of links that explain steam boiler replacement:

http://www.heatinghelp.com/article/11/Hot-Tech-Tips/234/Replacing-Your-Old-Steam-Boiler

http://www.heatinghelp.com/article/11/Hot-Tech-Tips/144/Boiler-Sizing

I've also attached a sheet that will help you compute the total radiator EDR and boiler size needed.

- Rod

Jamie Hall

Egad

Got to have those vents.  I hope you didn't throw them away; if you didn't, put 'em back and chuck the vacuum breakers.  If you did, sorry about that but the guy should have known better.  Get some new ones and install them.  And chuck the vacuum breakers.

Jamie Hall

And furthermore...

it occurs to me that anyone clever enough to remove perfectly good vents and substitute vacuum breakers may also have had some interesting notions regarding pressure.



Therefore, you should check the pressure settings -- if it is a pressuretrol, as I would imagine, it should be set at a cutout of half a psi, if it will go that low, and a differential (additive) of 1 psi -- if it will go that low.  Or as low as it will go, if that's higher.

TomM

whoa

did this guy get paid in full?  the job aint done if it dont work right.  don't answer this question.

-

anyway, first things first- get those vacuum breakers off, and the main vents back on. turn the pressure down. 

-

looks like you might be hangin out here for awhile.  Welcome!

Dave in QCA

make and model of boiler

What it the make and model of the boiler.  I want to find the installation and operation manual.  Would love compare the close boiler piping to what the manufacturer specified.

Charlie from wmass

Just look at the first and third photo

it is clear this is not this persons forte installing steam boilers. Nice guys I am sure and half the cost of those other guys.