Single Pipe Steam Main Return Temperature - Warm? Hot?

NancyQueensNY

Could someone please explain the basics of the temperature for Main return. I am observing room temperature pipe even when the supply mains are scorching hot. I believe the 2" main makes a loop totaling ~60-80ft ft. I am getting some plumbers say that the return pipe will be at most "warm", but not hot.

Is steam ever supposed to make it to the return or by that time all the latent heat juice is out and its all warm'ish.

ChrisJ

I would say it depends on how long the system runs and how hot the radiators are.

if the majority of the radiators are heated most or all of the way across it's likely the return piping will be quite hot, perhaps even close to steam temperature.

Under most conditions I'd expect them to be fairly cool though. My wet return gets very hot if it's below zero out but is usually barely warm.

If you're talking about a dry return (not along the floor) it also depends on where the main vents are. If the main vents are at the end of that return which many are, that entire return will be filled with steam and very hot.

Jamie Hall

As you may have concluded, a pipe will be steam hot where there is steam. Otherwise, maybe...

A true return -- dry or wet should never be steam hot, vents or no vents. If a system is really cranking -- long runs etc. -- a wet return may indeed become warm, but really should never be really hot. A dry return should never be more than warm.

There are two pipe systems -- such as most vapour systems -- which have all the venting at the end of the dry returns at the boiler. However, they have crossover traps from the steam mains to the dry returns. In those systems, the dry return is never more than warm, and usually cool.

All two pipe systems must have vents on the dry return, whether they have crossover traps or not.

The most confusing systems are one pipe parallel flow systems. They too may have all their venting right at the boiler, at the end of the pipe before it drops to return the condensate. If they do, that pipe is not, technically, a return -- it is still a steam main, even though it is past the last radiator runout. In such a system, that pipe will indeed be steam hot right up to the very last vent.

NancyQueensNY

Chris and Jamie - thank you both!

Yes it is a dry return, vent is at the elbow before the pipe dips down to go back into the boiler.

So if I remove the main vent at this spot for test purposes and run the boiler, should i expect to see steam come of out? (path of least resistance)

ChrisJ

Yes,
But please be very careful. That steam can cause severe burns extremely fast.

NancyQueensNY

I really appreciate your reminder, I am planning to stay away from the open pipe and turn off the boiler as soon as i can see steam... Im trying to diagnose the potential air-lock situation which is why I thin the dry return is never ever hot even after several hours of boiler runs.

New England SteamWorks

I would venture that your main vents are not working, so you have air in those dry returns and that is why they are cool. If this is so, after you install proper venting you will notice a large improvement in balance and efficiency.

MikeyP

@NancyQueensNY

I have a very similar setup as you. At one point my dry return, which ends approximately 2 feet from my boiler, didn't have any venting. It would only get slightly warm.

I have since added 2 gorton #2's and now that return gets steam hot. So I would agree with the others that running with it open at the end of the return should get steam heading there.

NancyQueensNY

@MikeyP, @ChrisJ, @Jamie Hall , @RI_SteamWorks - thank you all for your insights. Yesterday I was able to get the rusted vent removed form the dry return and left the pipe open to see if it gets hot... it did... but not very much, definitely no steam coming out of it, (even after leaving it open for an hour and with the Thermostat cranked all the way up; the boiler was running this entire time; gauge glass was half way, pressure was ~1.5 range)

Jamie Hall

Good show! Next thing to do -- after putting a nice new reliable vent on it so you don't have to worry about escaping steam! -- is to trace the pipe back and figure out a) how steam is supposed to get into it, assuming that it is and b) where along the pipe it stops getting hot. These things can take a lot of patience and ingenuity sometimes!

NancyQueensNY

For now, I purchased two Gorton #2 as advised earlier (these things look like UFO capable of carrying small aliens) and having plumber make the the piping which will looks like we are communicating with extra-terrestrials attached to the dry return.

Tracing the pipe is a mystery as it is inaccessible once it leaves the boiler room. Maybe if we can capture some aliens they can help trace it.

Could radiator venting in 1st and 2nd floor be an issue which is making the steam not travel all the way to the main vent?

ChrisJ

NancyQueensNY said:

For now, I purchased two Gorton #2 as advised earlier (these things look like UFO capable of carrying small aliens) and having plumber make the the piping which will looks like we are communicating with extra-terrestrials attached to the dry return.

Tracing the pipe is a mystery as it is inaccessible once it leaves the boiler room. Maybe if we can capture some aliens they can help trace it.

Could radiator venting in 1st and 2nd floor be an issue which is making the steam not travel all the way to the main vent?

Radiators can steal steam, and literally suck all of it out of the main.

However, you wouldn't see any pressure at the boiler if it was and you said you were seeing 1.5 PSI.

Abracadabra

pressure gauge may be wrong

NancyQueensNY

@Abracadabra - you are right, I should have a 0-3psi gauge installed. The current gauge is 0-30 - too broad.