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I need to remove a section of 3" copper, and replace it. Has anyone ever done this with a single Mapp gas torch? I'm not sure if its going to have enough heat to get it done. I probably could get it out without too much of a fuss, I just want to have a bit more confidence I can sweat the new one back in without making a mess.

I'd think it could be done with a pair of Mapp torches, but its probably generally done with acetylene?

  • Guessing, but if you focus on heating one area at a time and work your way around the joint I wouldn't expect it to be too hard. Yes, there's lots of heatsink area, but that's true any time you're sweating copper joints. If in doubt, you could always grab two pipes and a spare coupler and try the experiment "on the bench" before trying it for real... – keshlam Dec 17 '14 at 23:46
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You might have luck using two brazing torches, like these. My concerns usually aren't about making a mess; it's getting it to work without burning holes in it and physically getting it back together after a de-solder. I'd start over, but it's worth a shot on a $20 fitting. I'd say my re-solder success rate is 50\50 without doing more work than just using new, clean fittings. I've never done 3" and I wouldn't without a wrap-around torch head for an acetylene kit.

These brazing heads really are nice and make quick work out of plan old soldering.

ac brazing torch Source: refrigerationbest.blogspot.com

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I ended up getting it done without a fuss. It wasn't bad at all. I have very limited experience, and still struggle on 3/4" ball valves, but 3" copper is no big deal as it turns out. I used one of those hardware store Mapp gas torches and a half a tub of flux. Took a whole lot of sanding to get the old stuff down to bare copper, but the 40 year old copper had no problem, nice fillets all around.

For those wondering, I was putting a drain water energy recovery stack into a home with existing 3" copper drains. So, its no real pressure, just can't leak. My joints look way nicer than what the plumber did when the home was made. Looks like he tinned both ends and shoved the pipe in, theres no fillet but it looks like it never leaked.

  • I'm still looking for real-world info on how much energy DWER systems really save. Unfortunately my place's plumbing just isn't suitable for one -- I'd have to re-plumb all the grey-water drains, at least, to bring them together and make this work... and that seems to put it into the "forget it" price range. – keshlam Dec 20 '14 at 2:32
  • Well, if you've got copper drain pipes, any heat you're losing thru 'em is probably helping to heat the house so you already have a bit of recovery going. My question is 31% savings of what -- showers in particular (which it will do better on due to continuous flow), all hot water use, other... It does make sense, I just hope it pays off as well as claimed, esp. at today's copper prices. I keep thinking that there has to be a way to recapture more of the drier's heat... – keshlam Dec 20 '14 at 13:28
  • The problem with drier heat is that air doesn't have the surface-following or heat capacity behaviors water does, and if you have enough surface area to transfer the heat effectively you run into risks of lint accumulating and clogging the system. Best thought I've had would be to bubble the exhaust thru water before running it outside, extract the heat from the water, and change the water (and/or filter it, and/or refill it?) on a regular basis to keep lint from accumulating. I do have friends who just let the drier air escape into the basement thru a filter sock and then dehumidify... – keshlam Dec 20 '14 at 14:22

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