What is this \"trap\" and original flow direction?

Al Roethlisberger

I have an old(ca. 1929) overhead gravity hot water system that was converted in the early 1990s to a closed circulated hot water system, and I've had some questions about the direction(supply/return) they piped in the new(in 1991) boiler, and have believed for some time that it may be backwards.

Like a lot of these old systems, there seems to be some idiosyncrasies depending on the old men who installed it that leads to different answers on this topic, some contradictory, so I basically have to put together the clues and look at the system as a whole.

One clue may be represented by the "trap" outlined in the red rectangle in the photo below. Please take a look at the attached photo and see what you think this "trap" was for, and if it indicates supply versus return direction in any way.

Currently the water is returning to the boiler in the direction indicated by the red arrow. The green arrow would represent supplying water to the system.

I think I had read somewhere that a trap like this was to prevent reverse gravity flow, but am not sure, and am not sure if it matters if it were on the supply or return side.

Thanks,
Al

Mike T., Swampeast MO

On a relative scale at least, overhead gravity systems had abundant motive force and did not suffer from the same difficulties found in many multi-floor gravity systems. They were of course, VERY expensive--all that big pipe going to the attic never came cheap...

When your system was converted to forced flow, I suspect that the "trap" you see was intended to arrest gravity flow, but I highly doubt its effectiveness; especially on the return where the forces above would easily overwhelm such a shallow "trap" at the very bottom. Even if it were installed on the supply, I have a sneaking suspicion that flow in the system could reverse itself when the circulator is not running.

The original supply line(s) will be VERY large and will follow as short and direct a route as possible up to the attic with NO branches until the where the main(s) turn horizontal.

From the attic down, piping can get quite complicated in a multi-floor system. Remember that BOTH supply and return are moving DOWN towards the boiler. Usually the supply would be carefully "split" to supply rads that may or may not be on the same floor. Sometimes the return from an upper radiator can become the supply to a lower radiator. Were I truly a "dead man" I would have used the return from an upper floor bathroom to supply a lower radiator.

With the exception of what should be VERY short horizontals in the supply, everything horizontal you see in the basement should be the original return. In a larger home (where these systems were usually installed) I would expect to see a fairly complex system of returns in the basement, likely with two or more branches gradually increasing in size as they near the boiler location where they may have merged.

Bob Harper

chimney

I don't know about the trap but the venting has an issue or two. Black stove pipe is intended for solid fuel use only. The chimney must have a cleanout below the breeching. The chimney connector must be removable for inspection and cleaning.

I would recommend a level II inspection of that chimney.

Al Roethlisberger

The chimney venting is new


I had a certified chimney sweep/inspector out before last season, and he inspected both chimneys and even resealed the chimney breach/thimble after finding it was loose *shrug*

The boiler is gas fired, and came with the black steel chimney vent with auto damper. It is a Dunkirk boiler(rebadged as Carrier).

The chimney has a cleanout at the base.

Thanks,
Al