I dont get it...

Steam_Starter

I need a little head-clearing advice from the pros.



I understand the principle of venting the mains fast...get steam thru the system ASAP.



BUT



What is the principle behind venting the rads slow?  I have MOM's on all my 2nd floor rads and for s&*ts and giggles I pulled out the orifices to make them all vent equally.  Oh boy did all the rads heat quickly and evenly.  I never had a problem with quick and even heat before but this made it even faster.



Hopefully someone can shed some light on this...



Thanks,



JLG

Paul48

Slow and Steady Wins the Race

It's all about balance. Slow steady heating of all the radiators, slowly warms the whole structure.The EDR of your radiators should match the heat loss of the structure. When it's 50* outside, you won't need the radiator to completely fill with steam, or the room will over-heat. You've most likely heard someone that has hot air heat complain about being too cold, then too hot? You may also create a situation where the boiler starts cycling on pressure(short cycling), and it never use to.

Rod

The Benefits of Slow Venting on 1 Pipe Radiators

Hi- A lot of people ( I did) make the mistake of thinking that a radiator vent's sole job is just venting air from a radiator (and keeping steam in) but the radiator vent, by controlling the rate that the volume of air is released, is also controlling the rate of condensing occurring in the radiator.  When a cubic foot of steam condenses to water, it instantaneously goes from a volume of 1 cubic FOOT to a volume of 1 cubic INCH. This creates a huge vacuum which results in a large pressure differential that causes steam to rush into the radiator where it then condenses which then causes even more steam to rush into the radiator. This cycle will continue till the radiator/room heats up resulting in the condensing slowing down. 

     Typically what happens is that the large radiators are located in the downstairs rooms (closer to the boiler) and the small radiators are located in upstairs rooms (further away from the boiler) If the condensing in these large radiators isn't controlled, then it is possible for a condition to occur where these radiators will "hog" the majority of the steam available and "starve" the smaller radiators further away from the boiler. As the controlling thermostat is typically in a downstairs room containing a large radiator, the large "hog" radiator heats up that room causing the thermostat to shut off the burner before the rooms will smaller radiators (farther from the boiler) have a chance to properly heat up. Using a slower vent on the large radiators controls (slows) their condensing rate so that the steam is better proportioned to the other smaller radiators further from the boiler.  Slower venting can also help prevent overheating in the rooms with a large radiator and by controlling the rate of condensing, it controls the volume of condensate (water) being produced. This can help in some cases where a large volume of condensate is interfering with steam stream causing excessive noise ("banging")

   As excessive radiator venting doesn't seem to be a problem in your case, there could be several reasons for that. It maybe that most of your radiators are close in size and therefore close in condensing capacity or it could be that your boiler is slightly oversized for the system. Be happy that this isn't problem for you. It happens more when the boiler is closely matched to the EDR or slightly undersize.

You can also see here where having good main venting comes into play. If you have inadequate main venting, the steam moves slowly up the steam mains sequentially filling the large radiators first which may mean the thermostat setting is satisfied before steam even has a chance to reach the furthest radiator from the boiler.

- Rod



 

Steam_Starter

As usual Rod...

You helped clear my head.



That all makes perfect sense.  Thankfully, while my boiler is oversized, I think I really don't have an issue with short cycling on a pressure sense (from a slightly warm start to maintain room temp on an 18 degree night):



runs 20 mins

pause 5 mins

runs 10 mins

pause 5 mins

reaches temp



and does this about 3x a night.



As for the rads, they are all about the same size (except for bathroom and my daughters room...slightly smaller.)



I never looked at it from a condensing point...strictly air elimination.  Now it makes sense.



Thanks for helping me get straight.



JLG

Rod

Main vs Radiator Venting.

Since we're on this subject, you might want to take a look at the article written by Dave Bunnell, who is a "cutting edge" Chicago steam pro. Definitely thinking "outside the box!"



http://www.heatinghelp.com/article/323/Boilers/1551/Taking-Another-Look-at-Steam-Boiler-Sizing-Methods-by-Dave-Boilerpro-Bunnell