Wet return vs. Dry return

michael_15

Most of the diagrams I've seen of one-pipe steam systems have a fairly long wet return -- that is, about as long as the steam main.

However, my system doesn't really have one at all -- just a dry return. The return line is well above the waterline and drops to the floor for the first time right next to the boiler before rising up to meet the equalizer to form the Hartford Loop.

Is there a reason why systems were historically piped with a long dry return vs. a long wet return? Was/is one considered better?

-Michael

Alan(CaliforniaRadiant)Forbes

Excellent Question

I'm just a rookie at steam, but I'll venture to say that dry returns are preferable, but you can't always pipe it that way. Basements have living areas, doorways and windows and the return has to go underground to get back to the boiler.

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Fred Harwood

Dry vs wet

As long as the dry return gets no steam, it's OK. The main vent should be near the end of the insulated main, not furthing into the dry return.

Dave Meers

my two cents

Hi Michael,

Interesting question. One pipe systems do not normally have a dry return. These are usually just on two pipe systems. A dry return by definition is carrying air and condensate above the waterline of the boiler. The air is headed to an air vent, while the condensate is headed back to the boiler. There should never be any steam in a dry return.

A one pipe system can have a dry return if the end of the steam supply main is trapped. Then the portion of the return from the trap that is above the waterline can be considered a dry return, carrying just air and condensate.

Your steam main is considered a return after the last riser, but not a dry return since it still has steam in it.

There are pros and cons for having a long wet return or a short wet return. The building design and the preference of the original fitter usually determined what was installed. Long wet returns add water volume to the system and that can be a good thing. However they also tend to clog up over time and slow condensate return which is a bad thing. Short wet returns are easier to keep clear which is a good thing.

I hope this helps.

Best regards, Pat