Basement Ceiling Radiator: Slow to Warm

tlowc34

Sorry in advance for the long story, wanted to cover the background properly.

Here's my system: Dunkirk 200K BTU Boiler, 2 Pipe Trane Vapor System
Recent work: Replaced all main/return vents with B&J Big Mouths, asbestos removed, fiberglass insulation installed.

With all of the updates, the system has become much more balanced, steam travels through the mains and closes the vents in about 6 minutes after fire from a room temperature boiler. Radiators on the first and second floor are completely hot in about 12 minutes. All while staying under 1.5 psi on the boiler gauge - haven't installed the vaportrol and low pressure gauge I bought yet, I was planning this update when I improve the near boiler plumbing with a drop header. At this point I'm on to tackling the smaller problems: checking condensate return line temps to make sure traps are closing properly, checking valve stems for small leaks, and trying to figure out why the system needs makeup water (adds water for about 15 seconds every 8 hours or so).

In doing these checks, I noticed the ceiling mounted radiator (96" x 30" wall radiator, flat to the ceiling) in the basement was extremely hot, but only the first of 8 sections, the rest was ice cold, and the valve had a slow drip of hot water. I don't know if this radiator ever got hot or if it has always leaked, since my basement is workshop and laundry. I'm an Occam's razor guy (the simplest solution is most likely the right one) so I figured the trap is stuck closed, bad valve. Removed and disassembled and found the trap (trane B2) was not stuck closed and was relatively clean inside. I soaked and scrubbed clean while I had it out, but realizing this wasn't the problem, looked for another cause. The next thing that came to mind was clogging. So I pushed greenlee fiberglass fish sticks into the condensate tap and found no sludge or obstructions. I took a step back and remembered that due to the weight of the radiator and time (92 years) my floor joists had sagged. I jacked up the joists on either side of the radiator and sistered them to correct the dip in the living room floor before having the floor refinished last summer. Knowing that, thought it might possible the pitch could be off, causing a belly that prevents steam from making its way through the radiator. Checking it with a magnetic level it was still pitched but not much, so I adjusted it per the diagram and description below:



I set A at the highest point, with more drastic slope on AB than on AC. D being the lowest point. My logic being, I want steam to flow quickly across what is usually the 'top' side of the radiator (AC) and then down the tubes (AB, CD) When I did this, about 1.5 gallons of water poured out of the radiator. I thought, awesome, problem solved!

I wanted to see if unhindered, steam would make it completely through the radiator. So, leaving the condensate trap off, I fired up the boiler. Here's what changed:

1. The valve no longer leaked. My guess is the radiator was so full of water, that the valve was letting it escape through the stem. Either way, it stopped.
2. By the time the call for heat was over only 3 sections of 8 got hot.
3. Nothing ever came out the tap at D.

Being that it was bedtime for the kids I reinstalled the trap and called it a day.

I have a few theories, but wanted to get your opinion:

1. Ceiling radiators in a basement suffer from location. Lower in the system, they lose the effect of heat rising and in low pressure systems they take a long time to heat up. Since the system was originally designed for coal, this wasn't a problem since the heat was basically on all day. If all of the other radiators were satisfied and the basement radiator trap was open, it would benefit from greater pressure and get 'makeup' heat more quickly than it would at startup. Also, laying the radiator on it's side decreases efficiency, since the location of the condensate tap means 1/3rd of the radiator is water instead of 1/100th (ballpark). Knowing this, the dead men over-sized these radiators. Fast forward to today: this radiator will never get warm due to cycle times. The house has since been insulated and first and second floor radiators were sized pre-insulation and other radiators are able to satisfy the call for heat much more quickly.
2. Supply pipe is undersized. Coming off the main with a 1-1/2" pipe (like the living room supply next to it) would be beneficial to help the radiator get up to temp more quickly.
3. Position on the main is affecting performance. The living room is the largest room in the house and available steam ends up going there. I hesitate to even write this. The only way i would think this could even work is more about the vacuum effect of the system and the fact that the living room has a larger condensate return that would help draw?

Thanks for reading along.
-Todd

Jamie Hall

Those big ceiling radiators can be problematic. However, if condensate is able to drain freely, they are usually OK. They also, usually, are the very last ones to get hot all the way across. With vapour systems, like your Trane, it might pay to make sure that the inlet valve is actually fully open. It is quite possible that it was deliberately partly closed for balance. Lowering the pressure to where it belongs for a Trane (around 8 ounces) may also help a lot; at the higher pressures you are running if the other radiators have orifices or if the Trane valves are adjusted to the radiator size, those other radiators will be taking much too much steam.

Your theory that the modern relatively short cycles are part of the problem is probably true, too.

Heat rising is not a factor in vapour or steam systems; the driving force is the pressure difference, not temperature (and no, more pressure isn't going to help. 2 to 4 ounces should be quite enough!)

On leaks. You are adding way too much water. A gallon a month is good. A gallon a week is iffish. Adding water every eight hours is going to murder your boiler. It is surprising how small leaks add up. That one valve may easily have accounted for a couple of gallons a week, for instance. Look everywhere; valves are usually the worst culprits, but check your wet returns. You may have leakage or seepage there.

Was your system equipped with crossover traps, or had someone gotten creative and replaced them with conventional vents? The only vents should be where the dry returns join before dropping to the boiler inlet.

tlowc34

@Jamie Hall

Thank you for the super detailed response. I'm a bit of a noob, since I have only ever worked on this system in my own home.

Valve is completely open. Also, FWIW I thought on a two pipe the valve was ineffective at balancing? Basically, open and on or shut and off.

Makes sense about heat rising, but then why would the ceiling radiators be problematic? Shouldn't they warm up just as quickly? Is it the larger surface area of water that has a higher specific heat and has the effect of cooling down the steam more quickly than if the radiator was vertical? Essentially it's a huge pan of cold water for the steam to travel over and cool down?

That was my only leaking valve (one drip every 5 seconds or so when on), and my fill pipe is not very large (1/2"). Measuring exactly, I would say 5 seconds is a better estimate. I've heard it once a day while I'm home on the weekend, so I just assume every 8 hours or so. I wouldn't be able to guess on volume. The big mouths do let some steam out. Would my horrible near boiler plumbing be contributing to the water escape? I'm planning to R&R completely but buying large sizes threaded pipes in my area is a pain in the ****. The whole "do you have an account with us" - "no" - "okay, well then, that'll be a million dollars" combined with the "let me just see a list of the parts you need, then I'll pull them and tell you the price" rather than sharing a price list so I can find the most cost efficient pieces to use.

Since I have a pressuretrol instead of a vaportrol, the lowest readable setting is .5psi and the cutout is just ball parked at 1.5psi since I have no way of actually reading that. The gauge is not accurate. Boiler is off and cold right now (and no pressure, cracked the valve mine has at the top of the main) and it is reading .5psi. So my guess is that it is running at less than 1.5psi. I don't actually know, that's why I'm switching to vaportrol setup.

No crossover traps, but the previous owner hired somebody to fix her lack of heat in half of the house. Smart guy added a bunch of radiator vents and made a lot of things worse. Those are all pulled and plugged. The real culprit was the main vents. I will say this, I can understand people's frustration with steam at times. The Main vents installed originally are clearly going to eventually fail or at least not vent what originally spec'd for. This should have been positioned as a user serviceable, periodic maintenance piece, rather than call your tech. With those things not working basically everything else goes wonky. Love steam for a lot of reasons, but the venting piece doesn't make any sense.

tlowc34

Oh, also my mains and dry returns both have vents.

dopey27177

Does your system make and hold vacuum?

The ceiling radiators almost never got hot because low steam pressure could not heat the entire rad.

Basically pressure is not what makes heat. Volume of steam does.

When the system goes into negative pressure (vacuum) steam volume increases.

You may need vacuum in the system to pull the steam thru the radiator.

Jake

tlowc34

Yes, the system makes vacuum. However, I only know this in observing the suction that occurs if you remove a trap. Also, this was before adding the big mouths which I think would tend to reduce this effect based on how they're constructed.

Jamie Hall

Well... where you have a vent on a dry return and a vent on the steam main right next to it, that was almost certainly a crossover trap at one time. The system would work better if they were restored and all the venting concentrated at the boiler (which is, as you suggest, a user-serviceable location), but it will work this way -- provided the vents on the dry returns are at least as big, if not bigger, than the ones on the steam mains.

And venting a two pipe system makes a lot of sense -- if it's done right. The idea being dead simple: allow the air to get out of the steam mains and the radiators at as low a pressure as possible -- and ideally with both the steam mains and the dry returns at a uniform pressure all around; the steam mains at around 8 ounces and the dry returns at 0 (atmospheric). With crossover traps -- which have a huge venting capacity -- that's easy.

However, what's done is done.

I have to disagree with @dopey27177 ; it is pressure differential between the mains and the dry returns which moves the steam around. While inducing a vacuum in some manner it would have to be done in the mains as well as the returns to increase the steam volume; if it's done only in the returns it has much the same detrimental effect on vapour systems as raising the steam pressure does.

Inlet valves on two pipe steam systems -- particularly vapour systems -- can and frequently are set partly open, to meter the steam reaching the radiator. It is on one pipe systems where they must be either open or really closed, not in between. Many vapour systems -- and yours may well be one -- were actually very carefully set up, with the valves adjusted to ensure balance and "just right" heat in various spaces. Unfortunately, two things happen: first, someone decides to open a valve all the way. The other is that the pressure changes -- and due to the physics of the way fluids move through orifices, that will throw the whole balance off.

tlowc34

I have heard a lot about crossover traps. But never seen one. Just got LAOSH. Guess I have to some reading to do

tlowc34

I guess I'm more confused now, because the crossover would need to output condensate and cool air to the dry return. Then the dry return has a single vent before the drop into the wet. This wouldn't be close to the boiler. It would be in the same location as it is now, right?

Jamie Hall

Perhaps I am misreading your drawing? It looked to me as though the dry returns -- blue? -- all joined very near the boiler by the stairs, and I assumed that that was where they dropped to the wet return and the boiler?

The crossover trap does NOT handle condensate. That is taken by a drip to a wet return at that location. The crossover trap is located above the steam main, and allows only air to pass to the dry return.

dopey27177

To Jamiehall
When the vacuum is established a pressure differential is set.
2" of mercury is equal to 1 psig.

Lets say the boiler can produce 10" vacuum (mercury scale).

10" Hg = 5psi. add 8" pressure to 5 psi and the differential is 51/2 psi.

Check the steam tables and you will the lower the pressure the greater the volume.

tlowc34

Sorry @Jamie Hall I wasn’t really specific. In the laundry room (bottom left) there is an end to both a return and a steam main. They had gray trane bell shaped vents at the top, then they drop into the wet return. See the attached picture. I swapped for big mouths. The rest of the mains look like the other pic. I can’t find any seeping or leakage. However, at the doorway from the stairway area to the boiler room, the wet Return does drop into the slab. Maybe this is my water loss?

Jamie Hall

dopey27177 said:

To Jamiehall
When the vacuum is established a pressure differential is set.
2" of mercury is equal to 1 psig.

Lets say the boiler can produce 10" vacuum (mercury scale).

10" Hg = 5psi. add 8" pressure to 5 psi and the differential is 51/2 psi.

Check the steam tables and you will the lower the pressure the greater the volume.

Oh quite. And that 5 1/2 psi differential will wreak havoc with the calibration of the valves or orifices of a vapour steam system.