Radiators hot all-the-way across, but not as hot at bottom. Problem? Or normal?

Motorapido

My one-pipe steam system is nicely balanced. On days below freezing, they all heat the entire way across from inlet side to vent side. However, they are steam-hot at the very top and down about 1/3 from the top, and then the heat lessens as you go down from the top 1/3, and by the bottom they are just nicely warm all the way across. Is this normal? This condition applies to all of my radiators, some of which are vented with Hoffman 1a variable vents set to nearly closed, through Maid-o-Mist vents with the smallest orifices and also to two bigger end-of-the-line radiators on which my Maid-o-Mist vents are the next-to-largest and also the largest orifices.
Again, they heat super steam-hot and evenly from left to right from the very top and down about 1/3 from the top, but the heat lessens incrementally after that and ends with a very even left-to-right just-warm heat level at the very bottom. Normal, or should they be full-steam hot both left to right and top to bottom?

Jamie Hall

Sounds pretty normal. If you have a very very long run on a very cold day, do they get hot further down?

Of course, the bottom line question is... is the space comfortable? Can you reach the temperatures you want? If so, be happy!

JUGHNE

Are the air vents located at the top or about 1/3 the way down?

Motorapido

Even on super cold days, the bottoms do not get nearly as hot as the top 1/3. Vents are located at proper place, down low on the opposite side of the inlet. Valves are wide open on all radiators. I assumed this is OK, since it happens on even the slowest vented radiators. With those slowest vents, I could not imagine that the problem was steam rushing across too fast and closing the vent before all the air was purged from the radiator, but I figured I would check.

JUGHNE

Are the rads columns or have nipples across the top?

Fred

- Are the radiators properly pitched back towards the supply pipe? It could be that water pooled in the bottom of the radiators is causing the steam to condense.
- Also, what size are the supply pipes and the radiator EDR's? It may be that the pipes are too small to supply enough steam to fully fill the radiator.
- What is the steam output of the boiler? Has the boiler been down fired? Have you clocked the gas meter to determine that the gas supply matches the boiler input? Maybe be that the boiler is smaller than the connected radiation requires or that it has been down fired or the supply pressure from the utility company is questionable.
- It is also possible that you have the radiators vented down so much that they can't fully fill during a heating cycle. As has been asked, are the rooms comfortable? That is the big issue but you can open one of the vents more and see if/how that changes the temp of the lower portion of the radiator.

Motorapido

They look like the one in this picture.

Motorapido

Fred said:

- Are the radiators properly pitched back towards the supply pipe? It could be that water pooled in the bottom of the radiators is causing the steam to condense.
- Also, what size are the supply pipes and the radiator EDR's? It may be that the pipes are too small to supply enough steam to fully fill the radiator.
- What is the steam output of the boiler? Has the boiler been down fired? Have you clocked the gas meter to determine that the gas supply matches the boiler input? Maybe be that the boiler is smaller than the connected radiation requires or that it has been down fired or the supply pressure from the utility company is questionable.
- It is also possible that you have the radiators vented down so much that they can't fully fill during a heating cycle. As has been asked, are the rooms comfortable? That is the big issue but you can open one of the vents more and see if/how that changes the temp of the lower portion of the radiator.

Pitch seems fine. When I bought the house, there was water hammer at several radiators, so I used a level to check all of them and I shimmed the ones with hammer a good amount and the hammer ended. For the ones that didn't hammer, for good measure I added a little more shimming to what was already there.
I'll have to measure the supply pipes and compare that against the EDR. Pipes and radiators are original to the 1920s house, so I assume that The Dead Men piped the radiators correctly but you never know.
My boiler is 50% oversized. I have not down fired. I get several rounds of short cycles in cold temperatures. I have a vaporstat set to cut out at 10 to 11 ounces and back in at about 3 ounces. I am considering adding a timer in line with with stat to delay a minute or two or three between cycles, but that's a separate issue from what we're discussing here.
Rooms are comfortable and heat is pretty even throughout the house. Would you consider the smallest orifice on a Maid-o-Mist crazy small? Most of my radiators have Maid-o-Mist with the smallest orifice. On three others close to the boiler, I used Hoffman 1a vents turned just between off and 1 to slow them down a bit. I have a one-story first-floor bedroom addition from the 1940s with three radiators, over a crawlspace, while the rest of the house is over a basement. The basement stays quite warm due to the boiler (despite good insulation on all mains and returns and risers). The crawlspace does not get much air flow from the basement, so it stays around 63 degrees, while the basement stays around 69 or 70. Also, a prior owner did a renovation in that one-story bedroom over the crawlspace that required removal of one radiator. That one single room in this two-story house was always a good bit colder than all the other rooms, so that is why I run the smallest Maid-o-Mist orifices throughout the house and next-to-largest orifices in that bedroom. My observation of the temperature at the bottoms of my radiators is the same in all the rooms of the house, regardless of location and vent size.

Jamie Hall

Look. I'll say it again. If it ain't broke, don't fix it. Seems to me that you are heating your house nicely.

Now someday you will want to go with a smaller, more accurately sized boiler. That's true. But... your pressures are good, your heat is what you want. Be happy!

Gordo

Dear @Motorapido : If you have, as you pictured above, those really narrow tubed radiators in your house, they tend to heat up differently from the older more traditional style of radiators.

Below, for your amusement, is an infra-red video of a narrow tube style radiator heating up. Notice the steam as it enters the radiator shooting across the bottom "looking" for the way Out. That first burst of steam along the bottom is how it enters these radiators regardless of where the vent is placed.

If you look closely, you can "see" dark sections in the tubes in the front where the casting core sand did not get shaken out when the radiator was made.

The vent is mounted in the "wrong" place for... reasons (N.B. that's the way I found it).

Yet, the radiator kinda sorta heats up OK, I guess. Not as well as it could, mind you, but not bad considering.

https://www.youtube.com/watch?v=zskXv1COSvI

Motorapido

This is magnificent. Steam porn. Good info.

PMJ

The convection part of the heat transfer is colder air from the floor rising up through the radiator and exiting as warm air out the top. Therefore the bottom will always be colder. Totally normal.

Besides, when do we ever want rads totally full of steam? Never. What steam there is in them mostly rises to the top.

I keep reading discussions of rads not being totally full as some sort of problem. These systems were designed to run with the rads never being full - ever. Why is anyone trying to fill them now?