Would a "remote Hartford loop" cause any problems?

Erik_Midtskogen

I'm working on a two-pipe low-pressure steam heating system in a 164-year-old church. I have studied the basics of how two-pipe low-pressure steam systems are supposed to work, but I am certainly no expert on them.

The problem I'm currently trying to solve concerns keeping steam out of a very long condensate return line. This church's foundation consists of two small full-height basements—one at the eastern end, and another at the western end—separated by a roughly 80-foot-long crawlspace. The ground level of this crawlspace is several feet above the boiler's waterline. The boiler resides in the eastern basement. In the western basement there is no steam trap of any sort separating the steam main from the condensate return. As a result, the entire condensate return line going all the way back to the eastern basement is filled with live steam. This problem is made all the worse by the fact that this return line is ridiculously oversized at 2" IPS, parts of it are slightly buried in the dirt of the crawlspace, and the rest is basically lying right on the ground. Insulating that pipe would be a major project and the result still would not be ideal. Digging a trench the full length of the crawlspace and lowering the return below the boiler's water line would definitely work, but it's far too big a project.

I was thinking that the simplest and cheapest way of dealing with this situation is just to drop a loop under the far end of the steam main in the western basement. This loop will fill with condensate, and that will prevent the steam from travelling more than a few feet past the end of the main.

Would there be any problem with this idea?

Thanks,
Erik

Jamie Hall

Is there an independent dry return from the far end of the church? Or is that line which concerns you (quite correctly) supposed to be a dry return?

If there is no dry return, where do the returns from the various radiators go? And how are they vented?

A "normal" two pipe system will have at least two pipes, and very often three: a steam main, a dry return, and often a wet return. As you are probably aware, the basic operation is that steam is conveyed to the radiators in the steam main, while any condensate formed -- and the air which was in the radiators when the system started -- is sent to the dry return. There are several different approaches to keeping steam out of the dry return, but the important point is this: steam never reaches the dry return.

Now the steam mains also have air in them on startup, and that air has to be allowed to escape. There are three ways to do this: through the radiators and back to the dry return, through what is called a crossover trap (which is usually a standard radiator trap, but piped above the steam main) into a dry return, or through main vents. Any one of the three works, although the crossover trap is the simplest -- assuming there is a handy dry return.

Your long condensate line should never have steam in it -- particularly if it is also the air return for the radiators. That you have steam in it means that something is missing (besides being a waste of steam...).

So... your first step is to determine where the returns from the radiators in that west end go. To what pipe do they connect? That pipe must be protected from steam, and must be vented for the air, and must be pitched to the condensate can get back to the boiler somehow. It must NOT be directly connected to a steam main at any point. If there is a hard connection, that connection must be trapped or must be protected by a water seal. If it does have a water seal, there must also be a vent on both the main and the return at that location.

So... something is missing in your west basement. The "something", if that is the only return line, may have been a water seal -- which is basically what you are contemplating (a loop which goes from the steam main down to floor level and then back up to your problem pipe), and that will work -- but again, only if the steam main is vented in that basement, and only if the problem pipe is vented (probably at or near the boiler0. You could omit the vents in the west basement if the problem pipe is vented near the boiler by installing a crossover trap from the steam main to the problem pipe, in addition to the water seal loop.

To recap: your objective is to allow water and air to go from the steam main to the problem pipe, and keep steam out of it, but allow air to get out of it freely.

Erik_Midtskogen

Thank you for this information. I believe you have correctly understood the design of my system. Every radiator takes steam from the steam main in at one end, and drains the condensate into the return from the other end. There are two radiators located over the east basement (where the boiler is located). These are fed by their own steam main. This steam main has its own, somewhat large air vent at the end of it. The radiators each have their own smaller air vents mounted directly on the body of the radiator, as well. Each of these radiators drain their condensate into individual risers that go directly down to the wet return pipe that runs along the bottom of the basement wall, and back to the boiler's Hartford loop. It looks just like another low-pressure steam system I have gotten to know, and that one is working just fine. So, I see no serious issues at the east end of the system.

The issue is the west end of the church. It also has two pipes only. It is actually designed identically to the east end of the church, except that what would otherwise be a wet return is actually a dry return because that return pipe has to be elevated above the water level of the boiler in order to make its way through the crawlspace connecting the two basements. I'm confident that air venting is not an issue, because (just like the east steam main) the west steam main has its own air vent at the end of it, and even if that one wasn't sufficient, each radiator has its own air vent, as well. The big issue is that there is nothing stopping steam from the main from blowing through directly into the roughly 100-foot long, 2" IPS pipe that is currently acting as both a dry return and a radiator that provides heat for the earthworms, raccoons and stray cats that live under my church.

So, based on what you're telling me, the loop of pipe I'm considering adding near the end of the west steam main (that goes approximately 48" down to the floor and back) is called a "water seal", and as long as all the vents are in place, the system will function correctly during step-up and operation, allowing condensate to return to the boiler without allowing steam to go very far past the end of the main. I just want to make sure I'm not about to waste time and money doing something silly.

Jamie Hall

No -- that should work very nicely. The only real trick will be to keep your steam pressure down -- a 48 inch loop is only good for about1.5 psi before the steam will blow through it.

Erik_Midtskogen

Thanks for that assurance. I don't believe we get anywhere near a delta-P of 1.5PSI. One of our not-easy-to-fix problems is that our furnace is only 175,000 BTU, which is so small that I'm deliberately capping off one large branch of the system I haven't mentioned yet, with the goal of bringing the total EDR load down to around the roughly 450 square feet that our furnace can successfully step up and saturate efficiently. (A couple of electric heaters in the Sacristy hall will just have to do for now.) So, I'm not anticipating a fire-storm of steam blowing a high delta-P on our system.

kenlmad

I need to add a loop/drain to my system that was degraded by the previous homeowner that wanted pipes raised out of the way in their remodeled basement. The Lost Art book doesn't say what size pipes to use for the water loop. How do you size it properly? Would 3/4" work as long as the bottom of the loop is designed to be flushed to keep it clean? Thank you.

Erik_Midtskogen

I'm not an expert on low-pressure steam systems specifically, but my knowledge of physics tells me that the diameter of a pipe has no bearing on this area of concern, just the same way that the pressure per square inch exerted by water at the bottom of two buckets depends only on the depth of water in those buckets, and not on their width.

Jamie Hall

kenlmad said:

I need to add a loop/drain to my system that was degraded by the previous homeowner that wanted pipes raised out of the way in their remodeled basement. The Lost Art book doesn't say what size pipes to use for the water loop. How do you size it properly? Would 3/4" work as long as the bottom of the loop is designed to be flushed to keep it clean? Thank you.

That should work -- there's not much flow in there.

EBEBRATT-Ed

You can put a loop seal to keep the steam out of the return but you need vents at the end of the steam mains to get rid of the air.

The other solution which everyone will hate but will work is a condensate pump

mattmia2

Was this originally a 2 pipe air vent system or has it been knuckle headed in to one? The returns from each radiator need to individually go under the water line so steam from one radiator can't enter the return of another radiator.

Another option besides the loop at the far end to drop below the water line is a false water line at the boiler to bring all of that piping through the crawlspace below the water line. Presumably the original boiler had a high enough water line to keep all of that below the water line.

If you do a good job of balancing everything at least in theory the steam should partially fill all of the system but you will have to slow down the supply to the radiators that heat first to make that happen.

Erik_Midtskogen

No, this is a true two-pipe system. It would be hard to change that. All the gradients would have to be reversed over fairly long distances, or else the whole thing would very quickly flood.

The false water line is an interesting idea, but the crawlspace is so shallow that there is very little room for a riser at each end to keep a separate water line through it sealed. There are two radiators that send their condensate directly down into the dry return as it passes through the crawlspace. But those radiators are fitted with thermostatic steam traps at their return ends.

Jamie Hall

You don't need anything besides that water seal loop in the remote basement, and a vent on the steam main in there as well. Keep that line in the crawl space as a dry return, and vent it at the boiler or where it turns down.

Erik_Midtskogen

Will do. Thanks!