Unequal steam radiator heating

manus0142

Home steam system has two lines coming of the boiler. First line goes to 6 radiators at the back of the home. Second line goes to 6 radiators at the front of the home. Front hasn't worked hardly at all during the last year+. I had a heating company do the annual inspection. The second line is hot for about 4 ft. and then it goes cold. The heating company replaced the pipe in this area and it helped a little, but, very little. They brought and "expert" to our basement and he recommended wrapping all of the pipe in the basement with insulation and that would solve the problem. I wrapped all of the pipes I could get to recently. While we did see an immediate improvement in the front zone, it still radiates considerably less heat than the rear zone. The expert mentioned that the first (rear zone) pipe will be hotter than the second (front zone) since the steam gets to it first. The distance from the first zone outlet pipe and the second is only about two feet.

I'm at a loss as to whether I should just accept the unequal heating or put it out there for discussion. The big problem with this is the cost of gas (exponentially more expensive this year). I figure if the system is not functioning efficiently then our gas usage is greater. Last month the utility bill was over $600 and we don't have a huge house.
Any comments or discussion will be appreciated. Have a great day. Hurry up spring. We're in WI.
Thanks, JimM

Waher

@manus0142 0142
What do the air vents on the main steam distribution lines look like? Can you take pictures? Most likely you have insufficient air venting volume and installing several more main air vents will allow steam move through the system faster.

What is your pressuretrol on boiler set to? Can you take a picture of that? If the pressure is set too high it will slow down the distribution of steam throughout the system.

Jamie Hall

It does sound like a main venting problem. Are there any?

109A_5

Hello @manus0142,
If I understand your post correctly, a few years back it all worked fine. So to me the question is what has changed between then and when the performance significantly diminished. As others have mentioned, possibly the main vent is now plugged up or stuck closed. Could the return for that main be plugged up trapping condensate water where it should not be ? Did the house settle some more, pipe supports dilapidated, pipe pitch has changed.

Is it a one pipe system ?

yellowdog

i am definitely not a steam expert, but this doesnt sound right to me.

"If the pressure is set too high it will slow down the distribution of steam throughout the system"

Jamie Hall

yellowdog said:

i am definitely not a steam expert, but this doesnt sound right to me.

"If the pressure is set too high it will slow down the distribution of steam throughout the system"

Well, it isn't quite right -- but it's sort of right. It's a good deal more complicated than that, but ...

KC_Jones

yellowdog said:

i am definitely not a steam expert, but this doesnt sound right to me.

"If the pressure is set too high it will slow down the distribution of steam throughout the system"

To build pressure one needs to slow down the steam to build said pressure. Pressure is packing a volume of "stuff" into a space that is smaller than that volume. So yes, with a fixed output from a boiler, building pressure indeed means the steam is moving slower.

ethicalpaul

But it's often moving slower because it's already everywhere so moving faster wouldn't make any difference.

Or in the case of a really oversized system that builds pressure before the radiators even see steam, it's already moving as fast as the radiator venting will allow it, so it isn't going any slower than it would otherwise. In this scenario the steam is moving faster the higher the pressure is since it's going to push the air out of the way faster than it would at low pressure.

The statement is quite misleading and weird IMO. I think it's used to try to convince people that raising the operating pressure of their boiler is useless, and that is very true but I would use other arguments for that.

To try to make amends for this diversion, to the OP I would say don't use that company if they actually thought that replacing a steam pipe would help your steam distribution. It's like repaving your driveway when your car won't start.

The main venting that others mentioned is highly suspect here.

Jamie Hall

Agreed, @ethicalpaul . The real problem with high pressure or restrictions to flow in our steam systems lies in what happens when the pressure drops after the restriction, or as friction losses occur, and it's related to the fact that our saturated steam is very far indeed from being an ideal gas. In an ideal gas, as it expands in response to a pressure decrease, it also cools. Wonderful. Problem is, as saturated steam expands it too cools as one would expect -- but when it cools, it condenses, further reducing the pressure... and so on. This is great if the expansion occurs where one wants it -- in a radiator, for instance -- but is not quite so wonderful if one doesn't want it there, such as in an expansion from an undersized header to a nice big main, or going through a partly closed valve...

Thumbnail and incomplete sketch...

Waher

yellowdog said:

i am definitely not a steam expert, but this doesnt sound right to me.

"If the pressure is set too high it will slow down the distribution of steam throughout the system"

High pressure creates wet steam by increasing the density of water vapor compacted by pressure which slows down the steam moving through the system along with creating other problems.

Instead of trying to create higher pressure at the boiler compared to the lower pressure of the atmosphere at the exits of the air vents, it is better to create more exit capacity at the air vents. You want to create lower pressure at the ends of the system (vents) rather than trying to increase pressure at the entrance(boiler).

Picture you have a full subway train with doors on both sides. People are trying to get on a center platform, while others are trying to get off the opposite side of the platform. Does shoving people on the center platform harder onto the train get people off the train faster or create bunching (increased density) inside the train that makes it harder for the people trying to get off the train to leave? If you don't shove people (not increasing pressure at the boiler), and the opposite side of the train has nice big doors for everyone onboard to GET OUT quickly (what sufficient air vents do), suddenly the flow of passengers goes much more smoothly. Does that make sense?

Slow steam distribution almost always is because there's insufficient exit capacity for air (venting) so that steam gets trapped behind it in traffic. Increasing the 'traffic' (pressure leading to denser steam) isn't going to fix the exit capacity problem, but will make the 'traffic' problem worse because you are trying to solve for the wrong end of the equation.

Big Ed_4

The pressure is used to tell the burner to shut down when the system is full of steam .

109A_5

Big Ed_4 said:

The pressure is used to tell the burner to shut down when the system is full of steam .

Seems to me that is only true on a poorly designed or poorly maintained residential systems. Here, even on a 2 degree Fahrenheit day my pressure never went over 2 inches of Water Column or 1.156 Oz. I kind of wished it got colder out so I could see the pressure increase or the system just not keeping up with the heat loss. Even at 2 degrees Fahrenheit the Boiler seemed to only run at about 55 - 60% duty cycle, with only the thermostat terminating the burn.

clammy

Did your heating contractor locate and verify that your main vents are working ,if there are no main vents then they should cut in tees and install them ,if you don’t have functioning main vents your radiator vents will be doing all the work and it’s often difficult to get a system in balance without main vents . Did there expert check your radiators vents ,is it know what the edr of your existing radiators in comparison to the boiler edr . Is it possible the boiler is undersized or more common poor near boiler piping . Even though they stated they service it has anyone flushed and wanded and bottom flushed the boiler ? Build up of mud and rust in the bottom of a boiler can greatly effect its ability to produce dry steam. Usually one insulates there piping for a few reason but a contractor stating that this is the reason your rads don’t get hot sounds ridiculous , if every pipe was piping hot I doubt insulation is going to improve heat to the rads . I don’t think the steam-expert was a expert possibly just a new face . If you have main vents that are working and radiator vents that work your issue is else where .
Peace and good luck clammy

manus0142

Sorry for the delay. Right after posting initial comments I left for FL and it's been out of site-out of mind til now.

I was told the master vents had been replaced. I have the idea of switching the two master vents to see if there's any change in the line that is not performing now. BTW, the line doesn't heat up at all now but the rear house line still works fine.
Photos: I don't know if these photos will come through or not but here goes. Master vents, two outtake lines, pressure gage:

Big Ed_4

Insulate the header ....

Jamie Hall

How far along the misbehaving steam main does steam actually get? It should get hot right to the vent on that main quite quickly. If not, the "main" vent (yours are both almost certainly too small) may not be operating properly.

KC_Jones

I'm pretty certain those main vents are woefully inadequate. How long and what pipe size are the mains? With that information we should be able to recommend properly sized main vents.

manus0142

I insulated the pipe all the way to the last radiator stem. The overall length of the pipe to that point is approx. 50'. There are 3 sizes of pipe. I measured 3 2/3" OD from the boiler outward for the first 20'. Then the size steps down to 3" OD for 15'. It then steps down to a 2" OD pipe for the last 15'. After that, it remains 2" OD returning the approx. 50' to the boiler. The return pipe is not insulated.

Question: The rear zone going to the back of the house works fine while the front zone doesn't work at all. They both have the same size main vent. If the vent is too small then why does the rear zone work fine and the front zone not heat? Actually, the rear zone has a longer overall pipe run than the front. It doesn't add up to me. Thanks for you feedback.

manus0142

Additional info. I turned the system on and waited about 20 minutes. I checked the rear zone and all radiators were warming up normally. The front zone was warm for about the first five feet and then cold as a cucumber. Incidentally, the first stem leading to the living room radiator is exactly at that point. There are two radiators in the living room. One in the rear of the LR and part of the rear zone. It works fine. The second one is the above mentioned first stem on the front zone and it is cold. I hope this helps. Thanks.

Jamie Hall

If the steam seems to stop dead in the main, there may be a problem with a sag in that main. Check that the main is properly pitched for its full length. There may be other reasons, but that's an easy one to start with.

manus0142

No sag. Still clueless.

Jamie Hall

Oh well. As I said, that's the easy one. However, if steam makes it to a certain point in a system, and never gets beyond that point, there is something about that point. Which sounds obvious. One thing to remember is that eventually -- though it may take a lot of time -- even a pipe with a cap on the end -- no vent or anything --will warm up. If steam can reach it.

A complete block in a main is very unusual. However, if for some reason there is trapped water, that counts.

Can you take a picture -- maybe a couple from different angles -- of the point at which steam stops?

Steamhead

I bet the boiler water is dirty. I've seen contaminated water do some real screwy things like this. Drain and refill the boiler (NOT when it's hot) and see if that helps.

Replace the vent on the misbehaving front main with a Gorton #2. Is the rear main the same size and length?

manus0142

Thanks. Will do. Length of the working zone is longer by about 25'.

KC_Jones

Vents have a capacity to vent at a certain rate. If the mains are of drastically unequal length like yours, you need more or bigger main vent on the longer main than the shorter. The mains should both be fully hot prior to any of the radiators runouts getting steam. This shouldn't really take more than about 5 minutes to accomplish, it can vary by main length, but for a typical residence no more than 5 for me. Mine is 3 or less minutes for both mains to be fully hot. Main venting should be fairly aggressive.

As I stated above those vents are both woefully inadequate.

manus0142

Thanks. Do you agree with the above Gorton #2 size recommendation?

KC_Jones

manus0142 said:

Thanks. Do you agree with the above Gorton #2 size recommendation?

For the longer one, based on what you've posted that would be a good start, for the shorter one I'm not sure. Since you say they are 25' different from one another you will not want to vent both the same, you have that now and it doesn't work.

How long is each main from where it starts at the boiler, to the last radiator take off?