Steam System Short Cycling - Oversize or inadequate venting?

OldSteamy

My home was built in the 1940s and has a single pipe steam system. There are 9 radiators in total with a calculated EDR of 283. All have Gorton-style vents sized from #6 to D. The boiler is a Weil-McLein Model 68 at 465 sq ft. Last year I installed two Gorton #1 vents on both of the returns near the boiler. The boiler is serviced annually and the pressuretrol is set to cut out at 1.25psi (on a 0 to 3 psi gauge). The nozzle on the boiler is 110-80.

On a 2 degree set back, the system will run for 15 to 25 minutes and cut out on pressure. It will then cycle (on pressure) for about 2.5 minutes on and 2.5 minutes off around 5 to 7 times before the thermostat ends the cycle. The radiators closest to the boiler warm quickly while those furthest away will warm as well as hiss through the beginning of the cycling.

My question is whether the boiler is oversized for the system or should I be looking to increase the vents on the returns to Gorton #2 Eliminators. I feel the cycling is inefficient and simply is wasting fuel, which is very expensive. I have had many contractors at my home, however, most simply want clean the boiler, not troubleshoot the actual operation.

EzzyT

Your boiler is grossly oversized so no matter what you do with adding more venting it will continue to short cycle. Might want to think about replacing it with the proper sized boiler. If you have gas in the house I’d convert to gas. A Weil McLain EG35 or Williamson GSA100 will be perfect for your home. If you don’t have gas and have to stay with oil then the Peerless Ect-03-075 would match your system.

ethicalpaul

It’s hard to tell without a low pressure gauge that you can monitor to determine exactly at what point to pressure starts building but I’d offer:

- reduce your setback or eliminate it, then don’t worry. Steam pressure cycling doesn’t waste a noticeable amount of fuel.
- if your smallest radiator vent is a 6 your radiator venting is too large. The smallest should be a 4 or 5. A "D" is main vent size

OldSteamy

Thank you both for your comments. Looking for a contractor who services Northwest NJ / Eastern PA areas.

Jamie Hall

try @EzzyT who replied above.

bburd

It may be possible to downfire the boiler by installing a smaller nozzle. Check the the installation manual for the minimum firing rate.

AdmiralYoda

Do you have one or two pipe steam? Makes a difference on where to install the main venting. I also think you need waaaaaay more main venting. Probably two #2's or a single Barnes and Jones Big Mouth on each main, assuming there are two. You can't have too much.

The radiators are venting too quick and that won't help efficiency. Slower is better for the radiators. #4's on rads closest to the boiler, #6's further away. C's and D's are for huge radiators really far away like in a third floor attic.

OldSteamy

Thank you all for your comments.  Please help me to understand how increasing the time the air takes to leave the radiators improves efficiency?

Jamie Hall

OldSteamy said:

Thank you all for your comments.  Please help me to understand how increasing the time the air takes to leave the radiators improves efficiency?

It doesn't -- except in one regard. It makes it much easier -- sometimes even simply possible -- to get even heat from all the radiation, thus eliminating the tendency to overheat some spaces. Keep in mind that there are two very different and largely incompatible aspects to venting. One is to get the steam to each radiator in a reasonably close time frame -- the last radiator to get steam ideally should be no worse than a few minutes behind the first, even on a very large system. That's the job of the main venting and insulating the steam mains. The other is to control the heat ouput of the various radiators to match the space demand. That's the job of the radiator venting.

Ideally, the system will start all the radiators heating at pretty much the same time, and then run long enough to provide the desired heat from each radiator, and will then shut down on the thermostat.

bburd

There’s another possible issue as well:  if a radiator is vented too quickly, especially if its piping is undersized or poorly laid out, condensate may not be able to leave the radiator against the incoming steam as quickly as it is generated. On one pipe systems they must flow in opposite directions through the same supply valve and pipe.

This can lead to problems like air vents that leak or spit water, or become waterlogged and don’t vent properly. These can be especially severe if the system is started when completely cold, for example after night setback.

Slow vents like the Hoffman #40 have solved these problems on many systems.

dopey27177

I had a situation similar to this in my first house. I had a Richardson Pancake boiler that did the same.
I cured that by changing to a 4 degree set back.

Additionally, if the boiler is oil fired you can down size the the steam rating of the boiler by changing the nozzle. Replace the nozzle with a nozzle 10% smaller than the one in place. If you are gas fired call wiel Mc Lane and find out what it would take to replace the burner or gas nozzles to make a smaller fire.

That is curative. But it is worth doing all that to correct a problem that in reality is not a problem.

jake