Venting risers after the supply valve?

Jim_from_Worcester

I have a question regarding venting of my one-pipe steam system. I intend to vent my mains, and max venting would require 4 Gorton #2’s on one end and 3 on another. However, some of the risers are of considerable length from the mains and two even rival the short main in terms of volume (3ft^3+) and are 2-4 times the volume of the other risers. Having looked up some information from previous Wall posts and armed with Dan’s recommendation for venting oversized radiators, I thought it worth to ask if anyone has ever used the tappings on the radiators closest to the supply valve to aggressively vent the risers, as opposed to venting them before the valve, and a normal (say, Hoffman #6) vent in the typical far position to heat more slowly from that point. I figure this way I will have a better chance of balancing the system without all the hassle of tapping the risers.



The system is of modest size (267ft^2 EDR, radiators only, and 64 MBH), but has clearly been tinkered with (some of the radiators do not appear to be original). I have not performed a manual j for the house yet—I’m just getting my feet wet in that regard—to see if the system is sized properly. If my calculations are correct, the boiler (WM SGO-3) seems to be 34% oversized (358 ft^2 steam/86 MBH), but does provide DHW.



As a note, I still have the old asbestos on the piping (none on the near boiler) and plan to have it removed this summer and reinsulate. There appears to be a ¾” tapping at the end of the short main, but I can’t seem to locate one on the other main (I am hoping for a pleasant surprise when the asbestos is gone). So, in short, I won’t be experimenting with the vents until the fall, most likely. I was also wondering if anyone has had luck with balancing a system with the Macon or Danfoss TRV’s—seems like overkill for the $ but I figured I’d ask, especially if it could prevent buying additional vents for the radiators.



Thanks!

nicholas bonham-carter

Main venting question

If you can find a tapping at the end of the dry return (assuming it is a parallel flow system), then the main vents would be best there, close to the boiler where you can see their action.

These generous main vents work best at making all the radiators get heat simultaneously when the radiator vents are slower, causing the mains to empty of air, and fill with steam first before any riser has filled. A good low-pressure gauge will tell you when you have enough main venting, or you can calculate the volume of the pipes plus the volume of the boiler steam chest plus a fudge factor. The gauge is easier, as it will show the resistance of the venting to the air escaping, which is the key. 2 ounces is the ideal back-pressure during the venting phase, to prevent the gas company from making too much money from you.

Any insulation which is removed should be replaced with fiberglass, so you may wish to keep the asbestos insulation, and cover it. Insulation is very important to get the steam into the radiators without loss of heat from bare pipes.--NBC

Dave in QCA

Step by Step

I'm in complete agreement with NBC.  Address your main venting first.  Keep your main vents on the mains, not the radiators.  If you remove old insulation make sure you replace it with new.  If you do not have connections for vent, you can have a welder come out an install a "thread-o-let" on your main.  It is probably the easiest and cheapest option.



Remember, vent your mains fast and your radiators slow, very slow.   Once you have completed all of the above you can see if you still have any balance problems.  If you do, then you could proceed to venting that riser and/or increasing the venting on the slow radiator.

Jim_from_Worcester

My system

Is a counterflow arrangement. I do plan to vent the mains and insulate, no question there. I have tried to balance the system using the existing adjustable vents which I boiled in vinegar for about half an hour. I calculated the piping volume (but not the steam chest--I will add that in!) and set the vents according to a matrix for supply volume. The system was much improved after that, but there is still quite a bit of lag time between the first and last radiator starting to heat. I have adjusted the vents accordingly, but have not been able to improve things much since the initial changes.



Before I spring for new vents I wanted to explore these other options, however (venting risers and TRVs), especially now that I have the summer to tinker with it. I have seen many folks on this forum who have vented their risers on a counterflow system by adding vents before the radiator supply valve. I don't really want to do that. My question was whether I could get decent results--if needed--by venting the individual risers using the near-valve tapping on the radiator. It seems to me that the air would favor an aggressive vent close to the valve, and that is where the steam would arrive first, shutting that vent, which would allow the rest of the radiator to vent slowly through the far, normally sized vent.



It also seems to me that if that is the case then folks on this site would have already tried it--which makes me think I missing something, and I think that something may be this: when the steam enters the radiator with two valves it will push all the air out of the bigger vent first, regardless of where it is on the radiator, defeating its purpose of venting the risers only. I'm trying, like Dan says,  to think like steam, but I kind of lose my way here.



Thanks!

Dave in QCA

Last Resort

I think you will likely see great improvement when you at venting to your mains. 



However, in direct answer to your question, I do believe that I have seen a few threads where folks have done exactly what you're proposing and that it was successful.

Jim_from_Worcester

Thanks Dave

That is good to know if I still have some issues after the main vents go in.

Jim_from_Worcester

Thanks Mark

I will check this out. Been reading your posts about the Midco--great stuff. I am looking at a conversion with a Riello 40-G120. Do you have any suggestions of what I should be looking for? Per my plumber neighbor I am assuming I will need an indirect HW tank, but not sure what I should get--metal flue liner as well?

Jim_from_Worcester

DHW

Is supplied by a tankless coil--5 gpm. It already struggles to keep up with demand at times (laundry, dishes and bath time are not a favorable combination). We have two youngun's and often either my wife or mother-in-law are home during the day, but even so, I love the idea of the "scheduled setback." Not sure it's best option considering our situation.



My dream is put a one room addition on the rear of the house with solar HW, but I figure a small storage tank now to keep pace with demand could be scaled up later with a larger tank and heat exchanger. I will certainly take a look at Icesailor's post.



It is an oil to gas conversion. There is old supply line which is unused and I'm expecting will need to be replaced (I think the house was originally built with a small gas furnace and then converted sometime in the 1920's or 30's). I expected the need for the metal flue liner. We will likely install a gas range once we have a new supply line in.



Thanks for all the info.

Charlie from wmass

The gas line was probably

used for cooking and maybe hot water when the boiler was coal fired. If it comes in the basement wall it will need replaced.

nicholas bonham-carter

Counter flow measures

You could try putting a manifold on the last radiator of 2 gorton d's, with all the other rads vented slowly with Hoffman 40's.

Remember that you are balancing the system by having an equal resistance to the escaping air (back-pressure) on each rad, except for the last one which is now the main vent. This is where the 0-3 psi gauge comes into it's own by showing you that back-pressure (2 ounces)..--NBC

Jim_from_Worcester

Thanks Nicholas,

I will see where I end up when I put the main vents in.



Jim