Help me understand my mains

David Nadle

I'm planning to replace my boiler on a one pipe steam system. The pros I've brought in to look at the system have been scratching their heads a little when looking at my steam mains, and I'm confused too. Does this piping make sense? I'm afraid I'm going to have problems when the new boiler goes in.

The mains do a circuit around the basement, but the way the pipes are sloped it seems that the steam heads off in two directions then meet at the far corner. There is no main vent. I'd like to add one with the new boiler, but where?

The system worked pretty well last winter. A very small amount of hammer. And enormous gas bills...

I've attached a drawing. I'll be grateful for anything you can share with me and that I can share with the firm I hire.

[Edited to fix an error in the drawing.]

Brad White

Interesting

Nice loop- I have to imagine that your required pressure can be very low, ounces. If you have TRV vent valves on the radiators, the loop really becomes an asset because if one side of the house is in sun or is at temperature and the TRV's close, the steam will wind around the other way. Essentially your furthest radiator at any time is served by two mains, such low pressure is needed.

As for venting, obviously right now all air gets out by the radiators. If I were to put in a main vent, the highest corner (upper right at the 15" mark on your very nice diagram) would suit me fine.

The real key is the near-boiler piping. The full arrangement is not entirely clear. I would suspect that a good dropped header, decent equalizer and Hartford loop would do a world of good. You may even have them now, but it is not clear. Can you post a photograph?

Also, insulate the mains if not already.

What is the connected EDR and what are the pipe sizes? 2" all around?

David Nadle

So you don't have a problem with the slopes or the two mains meeting at the end? Good to learn. Unfortunately even though I measured 15" at that high corner there isn't really that much clearance there. I suppose we can put in a tee somewhere near the corner where there's room for a 6" nipple, etc. Right?

I didn't focus on the near boiler piping because I'm expecting it to all be replaced for a new boiler. There is a Hartford loop. If I understand the term correctly it's not a dropped header. Also, the header connects to the riser with a bullheaded tee (again, not an expert here) which I understand is not ideal.

It's 2" pipe all around. The pipes to the radiators are 1 1/2 except for one really small pipe feeding an upstairs bath, an obvious late edition. equalizers and the wet part is also 1 1/2. I do plan to insulate. I also plan to put trvs on the two upstairs bedrooms.

I'm expecting that with new equipment, vent, and insulation I'll be able to set the pressure low. The current stuff is so old I'm afraid to touch it. I think it's cranked up pretty high.

Many thanks to Mr. Holohan's books and this board for helping me be comfortable with all this.

Brad White

Slope of pipe

No problem with the slope, just noting that the steam and condensate are always flowing counter to one-another which slightly decreases the carrying capacity. That may well be the reason that the loop was made, to compensate for counter-flow.

As for venting, yes, go to a place as remote from the boiler as you can and with enough height to get a good main vent in there or make a Menorah up in the joists if you can. The mains should vent very nicely in both directions.

The bullhead tee is a no-no as you say; a challenge steam does not need. Even if you do not make a dropped header, a well-sized header with the take-off well downstream of the boiler risers will work well for you. If two risers off the boiler, exit the header downstream of both, not between them (you know this of course).

A good vaporstat to control in the range of ounces will be the icing on the cake. If what you have is "cranked up pretty high" yet only bangs occasionally, imagine what ounces will do.

Sounds like very large risers to the radiators. What is your connected EDR? What is your "A" dimension?

Do share photos, before, after and progress if you would.

David Nadle

EDR and boiler sizing

I have 280 ft^2 EDR connected. Another constraint that has popped up is my 5.5" flue liner. The boiler models with 5" flue are slightly undersized. Should I be concerned about a 3% to 5% deviation? Utica has a model that's right on the money. Any opinions on Utica?

David Nadle

Split loop into two mains?

Some of the pros I've been talking to about my boiler replacement have recommended breaking up my main loop into two separate mains and adding two main vents instead of adding a single vent near the high point of the loop. What do you think?

(I attached a diagram of the loop to my first post.)

Paul Fredricks_3

It seems to me...

That one side of the mains, from the high point to the boiler, is 1" and then reduces to 3/4". With the pressure up the steam will move fairly slowly so the condensate can get back through the 3/4". If the you drop the pressure down, the steam will move much more quickly and hold the condensate back.

I was thinking that all the main piping should run uphill from the boiler and the end of the 3/4" drop into a wet return. Either that or replace that half of the main with proper piping size to handle the radiation. Then vent the end of both mains.

And if the pressure is dropped, the vents on the radiators need to be pretty slow or the condensate won't be able to get out of the radiators.

Is this making sense or is my thinking flawed? (not hard to imagine)

David Nadle

All main pipes are 2\"

Paul, all the main (dry) pipes in the loop are 2".

The 3/4", 1" on the diagram are inches slope per 10 ft. Sorry for the confusion.

Paul Fredricks_3

Oops

Ok, that makes more sense.

clammy

counter flow mains

your steams mains are set up for a counter flow steam and condensate flowing in oppisite direction and i believe the pitch should be at least 1/2 per ft for proper operation ,you could disconnect the flange union and cut back and cap each branch and also add a main vent to each capped main ,re establish the proper 1/2 per ft back pitch on the mains and add a vent on each main,these type of systems love dry low pressure steam,get a vapor stat pressure control instad of the standard 1/2 psi cut out type which comes with the boiler .I would seperate the mains by the boiler if they are bull headed and do a nice over sized drop header and leave the main drips full size and drop to floor level with drains and tie them together before tieing into your equilizer and hartford loop .Also flush out your mains and insulate them this will help put steam where you need it and also lessen the amount of steam condensing in your mains and also lessens the amount flowing back to your drips ,to much condensate flow will eventually grove the bottom of your mains ,make sure who ever installs your new boiler and fixes your piping knows what they are doing and knows what they are looking at it's no place for time life heating contractors ,peace and good luck clammy

David Nadle

half inch per foot?

clammy,

From what I've read 1" per 10' is a good slope for counterflow. That's pretty much what I've got. It sounds like you advocate splitting the loop at the flange joint. Seems like you could eliminate that whole pipe at the bottom of the diagram by cutting and capping just after the lower left runout and ending the upper mains at the flange. You'd have to modify the pitch of the right-hand pipe to aim up instead of down.

I guess the big question is: does it make sense to do that vs. adding a single vent and leaving all else alone?

Jamie Hall

a comment on slope

it it isn't hammering, and you aren't seeing the boiler overfill (your condensate is getting back OK), it ain't broke and you don't need to fix it... the slope of the mains, that is!

V8toilet

The water hammer could be caused by the lack of insulation you have on your steam mains.

clammy

splitting mains

Even though i advocate splitting the loop and using 2 vents ,this is only because i have encountered a fair shair of counter flow systems is some older homes and alot of them operated very well and had more then 1/4 per ft back pitch on them and alot of them also ran out in what seamed like a single take off from the main header,in the other cases where the loops where step simalar to your set up and had no main vents and pitch was mimiun and intianal start up hammer was occurring it just seemed eaiser to myself to get what needed to be done done by cutting the main and capping both ends and adding main vents and it also made re pitching the mains a little easier ,it can sometime be hard to re pitch a main and still maintain proper pitch on your raditor supply run outs ,but this is jmho ,i hate complaints and a promblem not solved issue peace and good luck clammy