NEW TO STEAM!

MD402 · January 2012

So I’m a new homeowner in Northern NJ who just finished reading “we got steam heat” (what a huge help this book has been – thanks for all the post recommending it…)

I have a crown steam boiler which puts out 150,000 BTU/HR and runs on natural gas, feeding 6 radiators over 5 rooms (BTH, LR, study, Kitchen, DR) which equates to +/-1000SF all on the main floor. The previous homeowner put on an addition and eliminated all radiators upstairs (which I believe had two bedrooms and possibly a bath). This area is now heated with forced hot air. 

So here are my questions;

1) Is this boiler oversized? I have set the pressuretrol as low as I can get it (cut-in at 0.75PSI and cut-out at 2PSI) and the system cycles between cut-in and cut-out in 90 seconds and vice versa. I read a lot about the short cycling issue and believe this to be one but I can’t seem to find a rough timeframe to define short cycling. If this is a short cycle, what are my options to avoid this and save on gas? 

 

2) Hopefully you will be able to see the attached pictures, one of which is showing that I have two pressuretrols coming off one pigtail. The one to the left has the wiring going to the thermostat so I bottomed this one out to get the system to run at the above mentioned range. Any ideas what the other one on the right is for? It is currently set at 6PSI with a 1 differential which I have not touched.

 

3) The other picture is of the wire connection as gas control. The double headed wire is not connected to anything and I’m not sure if it should be. The system works well besides the short cycling. I checked the low water cutoff and that works. The other end of the double headed wire goes to the low water cutoff and the pressuretrol on the right set at 6PSI. Any ideas on this?



Thanks for the help – it’s much appreciated. My curiosity is getting the best of me on this stuff…

Abracadabra · January 2012

...

You need to calculate the total EDR of the radiators you currently have. Compare this to the sq.ft. of steam provided by the boiler.

The cut-in is a differential. You need to increase this. ie. You have cut-out at 2psi and cut-in differential at .75psi, so it's cutting back in at 1.25psi (2-.75)

The cycle is from when the thermostat calls for heat, till it's satisfied. Not the time from cut-in cut-out on the pressuretrol.

There are usually 2 pressuretrols, one as a backup to the other in case 1 fails.

Can't really tell what's going on at the control. A better picture with the wires kind of spread out and labeled may help.

lchmb · January 2012

betting

the two wires connected together at the gas valve probably used to go to a roll out fuse on the front of the boiler (guessing only). Have you had the unit serviced? Might be worth it to have someone come in and check the safeties, test gas pressure's and service the boiler...

Mike Kusiak_2 · January 2012

Cycling on pressure

From what you have written, it would appear that your boiler is about twice the size it should be now.

You mention that all the second floor radiators have been removed so this is the first clue. Secondly, short cycling on pressure with a 90 second on, 90 second off pattern confirms that the boiler produces about twice as much steam as the current set of radiators can condense.

Unfortunately there is not much that can be done to reduce the firing rate of an atmospheric boiler without reducing efficiency, so you are pretty much limited to living with the pressure cycling.

The second pressuretrol is a safety backup to shut down the boiler if the steam pressure exceeds the first pressuretrols working limit.

It appears you might have a powerpile gas valve on that boiler. Can you operate the heating system independent of AC power? is there any shut off switch connected to the electrical wiring of the house?

NEW TO STEAM!

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