Only first sections of radiators getting hot. Why?

Joseph_4

I have a case where three radiators in house are only getting hot up till the first half of the radiator's sections. They are quite large maybe 10-12 section column type radiators. The cut in pressure is at 1/2 pound on the pressuretrol. I removed the air vents completely (after boiler was already fired for say 20 minutes)  to see if they'd get hot. One got completely hot in about 10 minutes with air vent removed. The other one finally got completely hot after about a half hour after removing air vent. I didn't put a level on radiator yet.To the eye looks like radators are flat on ground with little to no pitch. What causes the problem I'm seeing with these radiators and what is the solution? 

Thanks

Joe

MichaelK

Check a few things

It wouldn't hurt to check the level.  Also you may want to replace the air vents if the radiator got hot after you removed them.  As far as it taking so long, what is the cut out setting for the boiler?  How much steam does the system build up to.  Also is it one pipe or two pipe?  Are your traps working on the radiators?  They could have water laying in the bottom.    Just some things to look into. 

BobC

radiators not heating

Is this single or two pipe steam?



You mentioned removing air vents so I'm assuming single pipe steam. Are the main air valves working and are they large enough? What model are the main air valves and what size and length is each steam main? If you can't vent the air the steam will not get there or will get there very slowly.



Check the radiators and the piping with a level, don't trust your eyes. the radiators should slope back towards the supply valve. Then check the radiator piping to make sure it allows condensate to run back towards the boiler.



You mentioned the cut in pressure is 1/2 but what is the cut out pressure? If the gauge doesn't read what is the white knob inside the pressuretrol set to? Also is the water level in the gauge glass bouncing around a lot?



After all that you will have to determine if the individual radiator venting makes sese.

Patrick_North

Maybe nothing's wrong...

So, are the other rooms of the house nice and warm while these three rooms are cold? If not, you probably have no problem.

Radiators will warm up left to right or right to left over time as the thermostat continues to call for heat. If the thermostat is satisfied and the radiator didn't get hot all the way across, then (assuming the room was heated adequately) it's either not that cold out or your radiator is bigger than it needs to be. You mentioned that these rads are especially large, so this wouldn't be surprising.

If, however, these rooms are not getting warm,you may need a different vent that can vent air more quickly.

If you don't already have it, Dan Holohan's "We Got Steam Heat" (available through this site) is a GREAT primer on the subject, and something every homeowner with steam heat ought to own.

Good luck!

Patrick

rcrit

how level is level?

When leveling a 1-pipe radiator, how out of level does it need to be? Is there a rule of thumb on it? I've got a 10-section sagging pretty well in the middle, does that mean the vent-side needs to be way out of level to compensate?



I guess that if you go too far you risk dumping goop into the system and/or having the condensate rushing out too fast causing water hammer, right?

BobC

sag

A radiator needs to be sloped enough to make sure the condensate can drain out. You right about being careful not to overdo it.



As to a large radiator with a sag in the middle I don't know what you can do but try and shim it so water can drain out. You may not be able to get it all to drain but perhaps you can find a happy medium by trial and error. Does that radiator hammer now?



Bob

rcrit

droopy

Is heat and quiet good enough to gauge that the slope is right?



It occurs to me that last winter this rad never heated all the way across (ever). I had stuck my 2ft level on it  last year and of course it looked fine. I got a spiffy new 9" magnetic level and that's when I found the sag. How does one go about testing something like this? Mess with the level then crank up the thermostat to see if it heats all the way across or just wait for a really cold day?



This seems very much more art than science :-)

BobC

shim

Does it heat the room adequately? If it does than the best part of valor may be to let it be.



If not shim it up a bit (1/8 to 1/4") and see how it works. Be careful when levering it up not to crack anything, if it's really heavy lever it from a couple of spots to spread the load. Then crank up the thermostat and what happens. The wind is starting to blow and the temperature is dropping here on the coast in Massachusetts but you might be warmer.



 Also make sure your venting it fast enough, a large radiator needs more venting.



Like most things there is a lot of "art" involved in balancing steam systems.



Bob

Big-Al_2

Boiler Big Enough?

Is your boiler making any pressure at all, even if it's left on for a long time?  If not, it could be undersized for the amount of radiation connected to it.  If it's too small, all the steam will condense before it can reach the far end of at least one of the radiators.



A steam boiler needs to be sized for the connected radiation, not the heat loss of the house.  Not all heating contractors know this, and when they size up a boiler, it can come up short.  You could find a radiator chart online, tally up the sizes of all the radiators, and compare it to the ratings on the boiler you have.  It would be a good place to start. 



Alternatively, you could close the vents on a couple of other radiators by removing and plugging them, or they often will close by simply turning them upside down.  If the problem radiator then heats up OK, then you will have your answer.