Trap in Condensate Return Piping


Old 01-02-17, 08:56 PM
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Trap in Condensate Return Piping

We have a two-pipe steam heating system in our house (1918). The condensate return line that exits through a bathroom floor has rusted out and broken off.

There is no access under that bathroom. I can route the condensate return line through a wall, and then in to a crawlspace, and then into my basement where the boiler is located.

Because of the spacing, I will have a slight u-trap (2" of rise) in the condensate return piping. Is this permissible on my low-pressure steam system? [My condensate piping is pure gravity feed, there is no condensate pump.]

I assume that the trap I would create would stay full of water, but old condensate would u-tube on down the line as steam filled that radiator. The bottom of that radiator might stay wet by 1/4 to 1/2". I didn't know if that would create a problem, so I thought I would ask the experts here.

-- I think the correct way to do the project would be to hang the radiator about 6 inches higher and then re-plumb. However, that makes it a much bigger project, and I have to mess up my wife's nice finish on the bathroom!

Any advice would be appreciated.
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Old 01-03-17, 10:01 AM
Join Date: Oct 2013
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To make this as simple as I can, all pipes must be pitched towards the boiler for proper condensate drainage. If there is condensate that stays in the rad and does not drain the rad will not heat and when the steam meets the water you will get banging and a very noisy rad. Depending on the amount of water sometimes violently noisy.

Chances are the water will continue to collect and back up into the supply line for more problems.

The bottom line is no traps unless it's a condensate trap on the rad when the job calls for it.

Dan Holohan has some great steam books out. He is the steam guru. You may be able to google him or you tube may have some more info.

If you're interested in steam he has a book THE LOST ART OF STEAM. A must read if going to work with steam, also you can go to which is his web sight.

Hope this helps a little.
Old 01-05-17, 10:15 AM
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Thanks for the help. I knew I wanted to keep my gentle pitch, but there is just no way to get pipe from Point A to Point B without creating a trap at some location along the run.

The good news is that the "rise" of the trap would just barely be above the condensate pipe exit on the radiator. Theoretically, steam pressure of 0.43 psi should be able to "lift" water (condensate) by 1 foot. I thought this might be enough pressure to clear the small level of base water in my radiator on each cycle.

I will certainly check out your recommended help source.

Any other thoughts from the experts?
Old 01-06-17, 09:31 AM
Join Date: Jan 2014
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I'm not an expert in steam heating, but...

Could you find a low spot to install a condensate pump that would pump back up to the existing pipe?

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