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Interesting Buried Condensate Line

Harry_6 Member Posts: 141
Recently, I was looking into a heating system in a mansion, in which the owner reported slowly losing boiler water. Well, you guessed it, he said he had a buried condensate return line. The good news was that this pipe was buried under a brick floor and was only about 10' long (I was assuming concrete or something equally horrible). The potentially bad news was that it was reported to be imbedded in concrete where it went under a load-bearing brick wall. Potentially terrible, again. But what I found was far more interesting. As the attached photo shows, the 2" return was encased within standard (for 1915) cast iron drainage pipe, within which there appeared to be an air gap between the inner and outer pipes.

Now if you've ever tried to plumb one pipe inside of another you know it isn't as easy as it sounds. How do you install and elbow inside another elbow? Well, their solution was this: The end of the pipe visible makes a 90 and comes through the floor, where the gap between pipes was filled with some kind of asbestos material. The outer cast iron elbow isn't a 90, but a drainage tee, since the radii of the inner and outer 90's aren't compatible, and the inner pipe would be displaced by contact with the outer at the turn. Using a (plugged) tee fixes this. The other end of the pipe(s) does go under the wall, but since it's the outer pipe imbedded in the concrete, it was possible to extract the inner without trouble. Once through the wall the inner pipe emerges into a small concrete pit (only about a foot cube) and was tee'd back to vertical with a small drain cock to allow draining the otherwise always-filled, buried portion of the line.

The inner pipe, when extracted, was in perfectly good condition, since it was never in contact with the earth. Ironically, the water loss was because the little pit had been full if cinders for years, and the threads where the drain cock was tee'd to the 2" line had rotted out. The actual buried line, although about 30% filled with sludge, was otherwise fine.

This was, by the way, a Mouat system, retrofitted into the 1880's home of a wealthy merchant, circa 1915, and was, needless to say, very carefully designed and executed. Which may be why they took such care in installing this buried return. Because this was a Mouat, the return temperature was probably never more than around 100 degrees, so I'm thinking the elaborate installation was more to protect the pipe than insulate it.

Has anyone else come across this kind of installation?

P.S. - I'm installing a new 2" black line inside a 4" PVC casing. We'll only have to wait another 100 years to see how well it holds up!
New England SteamWorks


  • Steamhead
    Steamhead Member Posts: 16,727

    Be sure to post the after" pics!

    Do you have one of the little pit where the drain cock was?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • kcopp
    kcopp Member Posts: 4,393
    Well I'll ask.... Why not do it in Copper?
  • ratio
    ratio Member Posts: 3,605
    I have an underground condensate line enclosed with drain tiles too, it went into the ground c. 1950's. Unfortunately mine leaked, considerably, before I came on & had it repaired.

    I found the leak with a Fluke VT-04, a big roundish warm spot on the floor. The plumber called in the middle of the repair to tell me he couldn't find the condensate line, all he could see was a drain pipe of some kind... He was kind of reluctant to bust it open, for understandable reasons!

  • Harry_6
    Harry_6 Member Posts: 141
    Here are a couple pictures of the condensate line as I found it entering and exiting the floor. The little square pit is less than a foot deep. It appears to be poured concrete, but the cinders filling it conceal its exact nature. It probably filled when they scrapped the coal boiler and the cinders stayed there, slowly rotting the nipple into the cock

    I did weigh my options for replacement carefully. I considered copper, black, galvanized, even stainless, but eventually eliminated them one by one. Galvanized is not to be used for steam (although no one seems to have the definitive reason why); stainless would be great, except it's expensive and hard to thread; copper is ok, but I worry about expansion stresses on the sweated joints and having to worry about electrolytic action between iron, damp earth and copper; and I had a hole big enough for a 4" pipe, so I'd have to ad fill. And what about there being insulation value in the air space but not with direct burial? Did I want to use some sort of water resistant insulation, like perlite? In the end I decided that I would just copy what Mouat did and use black inside an outer pipe. After all, he was better versed in it than I.

  • New England SteamWorks
    New England SteamWorks Member Posts: 1,502
    You might want to "Gerry Gill" it instead:

    New England SteamWorks
    Service, Installation, & Restoration of Steam Heating Systems