Steam system cycles constantly

big_giant_house

We are new owners to a PA oil-region home my daughter has aptly dubbed the "big giant house."  It has a steam system dating from the late 1800s that is set up to heat two floors, approximately 3,400 sq. ft.  We also have a high efficiency new furnace retrofitted into the second floor and third floor tower room.  We were not sure the steam would even work, but we found someone who does work on steam (though not by any means exclusively) who just got us up and running (and installed a new power vented blower to the outside).  He says the furnace is fine and that it is  burning gas at about 80-83 percent efficiency.  All the radiators will heat up completely when the furnace is first turned on.  There are about ten radiators ranging from five to fourteen sections.  Half are short and half are the tall, ornate Victorian ones.  Once the temperature is achieved (65 degrees), the furnace then continues to cycle on every few minutes, at least six times per hour.  The gas consumption is very high.  He thinks it is the thermostat or that the furnace is now oversized for the house and building up pressure too fast.  He wants to change the thermostat and take out two burners in the furnace.  Does that sound right?  We want to use the steam system if possible, but the cost may just be too high.  We hate to turn  these radiators into the most ornate plant stands ever.  Any ideas on what steps to take first?

Rod

Steam System

Hi- Your description is a bit confusing. You use the term "furnace". " Furnaces" heat air. Boilers heat either hot water or steam so I when I refer to "boiler" it will mean the unit that makes steam for the first two floors. I have a couple of questions.

Questions:

1. Is the steam boiler new?

2. If new, were the radiators measured and the boiler sized to match them?

3. What is the maximum pressure that the boiler achieves before shutting off at the end of a cycle?  It should be 2 PSI or less.



Thermostats-  The thermostat you use for steam should have a settable cycle per hour function. For steam this is normally set to one cycle per hour. This means that after the thermostat reaches the temperature set on the thermostat, it won't start again for one hour. This allows the hot radiators to "coast " for a while and heat the house.

I  would get the right type of thermostat as the first priority and see what that does. There are also other things that need to be checked before thinking about trying to down fire the burner. Down firing is a bit tricky.  I might mention some cycling is normal during the fall and spring when the outside temperature is mild.



Since you are new to steam you might want to get a very good book available in the "Shop" section at the top of this page. The book is "We Got Steam Heat!"

http://www.heatinghelp.com/products/Books/5/61/We-Got-Steam-Heat-A-Homeowners-Guide-to-Peaceful-Coexistence

It's written for the homeowner and is easy, humorous reading. In a few evenings reading your knowledge of steam systems will be light years ahead.

- Rod

big_giant_house

corrections

Yes, quite right.  Sorry.  The basement has a  boiler system to fuel the steam radiators and the second floor has the gas forced air furnace.  The heat contractor did not do any measurements, which makes me wonder too about taking out burners.  It sounds like a lot of experimentation.  Also wanted to add that when I say the system is burning a lot of gas, I mean it went through 25 ccf in one 24-hour period with the thermostat set at 65 (so we've shut it down essentially pending further investigation).  Perhaps this is normal for a house this size, but it seems to me something is not working properly.  I'll get the books!  Thanks for the advice.  I think also we may want to look for specialists in Pittsuburgh or Cleveland? 

big_giant_house

and also...

No, the boiler is not new.  It is probably thirty years old.  That made me wonder about the 80-83% figure.  I assumed it would be way down in the 70% range for fuel efficiency.

big_giant_house

and also...

No, the boiler is not new.  It is probably thirty years old.  That made me wonder about the 80-83% figure.  I assumed it would be way down in the 70% range for fuel efficiency.

Blackfoot

Steam system cycles constantly reply

Sounds like you have a standard heat controller that is set at 65 degrees F. If so, these controllers do toggle on and off to maintain your desired temperature setting. The degree of toggle depends on controller type, anticipation, location, heat loss, radiation, and air movement. Another condition I have found is when the radiation service valves or air vents on the radiators are closed causing the burner to cycle off on high pressure with a close differential. As an example; your boiler fires up to lets say a cutout of 3PSI because your radiators are 80% closed creating a back pressure that shuts the burner off until the pressure drops back to the differential setting, lets say 1PSI. You can see how this could drain your fuel supply quickly while giving you little if any heat. I configured a 32 unit property I service to run on 0.25PSI (1/4 lbs. of steam pressure). I heat one two story and one four story building at this site using one Tekmar steam boiler controller elliminating the troublesome themosthat location syndrome in multi-unit properties.

To minimize the toggling frequency, you will first need to determine if you have a back pressure problem and if not, find a controller with differential capability. This device will allow you to overshoot your setting (65F - 70F thereby giving you a longer off time.

Based on a guess of your existing burner GPH firing rate, I would advise against modifying or reducing your boiler output since it would take loinger to heat your home which means more fuel cost.

There are many schemes available to accomplish your needs but be sure to engage a qualified steam heat expert to assure your satisfaction. A heat loss calculation will validate if your existing system is sized properly. Do not take chances, steam boilers are potential bombs in the wrong hands but are highly efficient in the right hands. Also remember that steam boiler safeguards are monies well spent and will better protect  life and property and possibly reduce your insurance risk.

Hope this is helpful.

Art

Rod

Oversized Boiler?

It sounds like there have been a lot of changes in the heating system (s) in your house.

Were there more steam radiators originally attached to the boiler? If so it may be that the boiler is now way oversized which means it produces much more steam than the present radiators need. This would cause the boiler to cycle a lot.

If Cleveland is near you, you are in luck!  There is a really good heating pro located there by the name of Gerry Gill.  If steam pros were rated, he would easily be in the top ten in the U.S. Here's is a link to his website: http://www.gwgillplumbingandheating.com/

He's an a expert on getting old steam systems up and optimally running. If any one can get you straightened out, he's the guy to do it.

- Rod

big_giant_house

Thanks

Thank you for the information!

big_giant_house

Will check this out

Yes, there probably were at least three additional radiators on the system, plus there has been a lot of insulation added to the house since these were put in.  I'll check out the fellow in Cleveland.  We are a couple of hours away, but it is worth a shot.  Thanks!

Rod

Thermostat

Check your present thermostat and see if it has a settable cycle per hour function. If so set it to 1 cycle per hour.

 I have a Honeywell Vision Pro 8000 Model TH8110U  which among other things has a settable cycle function. The main reason I got it is its big well lighted screen.

I've attached the install manual so you can see the different functions.

- Rod

big_giant_house

thermostat

Thank you.  I'm checking our thermostat now.  It is a Honeywell,  but I cannot find any way to change the default cycle.  I'll take a look at the one you suggest.  Rhonda

BobC

Thermostat

If you don't have the manual for the Honeywell you have now you can probably download one - http://www.yourhome.honeywell.com/home/Products/Thermostats/SummaryList.htm



If you find the model number of your thermostat and click on the details button you should be able to download the manual.



Bob

AlexR

cycles per hour

A different (and slightly less ideal) way to fake a cycles per hour setting on a thermostat that doesn't support it is to set the dead zone or swing- how many degrees below the setting must the temperature be before the thermostat calls for heat again.  If you set this to two or three degrees then your thermostat won't call for heat again for a while (depending on outside temperature, insulation, how many windows you left open,...).  I run mine this way because I don't mind a few degrees of swing.  In your case, it may be an easy way to experiment with the controls without replacing the thermostat.

big_giant_house

Found it!

Thanks.  I was able to poke around on the site and download a manual last night.  I reset the cycle for one cycle an hour and have begun to write down how often it cycles.  So far, it seems to be cycling less than once an hour - we are coming up on two, but the house is staying near the 65 degree mark.  I think this is a drastic improvement over six to eight times an hour!  I'll check gas consumption for a couple of days to see if there is still some problems, but this has helped tremendously.  Thanks for the help!

big_giant_house

Cycles

Thanks for this advice.  I was able to locate the cycle control on the thermostat, but I'll have to monitor it for a while to see if it is working properly.  If not, it might make sense to go to a simpler thermostat. 

Rod

Thermostat Set Back

Hi Again-  Since we're discussing thermostats, I thought I'd better mention that the consensus on the "Wall" (or as one of the members, Jaime added, "for last winter") is that on a steam system, using a setback of more than 5 or 4 degrees is counterproductive as it takes more fuel to make up the temperature difference than just to maintain the original temperature.

Great to hear that your present thermostat has cycle setting ability. As for find a "simpler" thermostat I'm not sure there is such a thing. They all have 20 times more "bells and whistles" than anyone needs.

- Rod