Click here to Find a Contractor in your area.
In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Need to contact us? Visit

Short Cycling on Pressure? Downfire? Air Vents?

ST140ST140 Member Posts: 41

I tried to put as much info as possible in here up front...

Hello All - last time I posted I was asking questions about EDR and which Megasteam best fit my needs. My total EDR was 415 and so I went with a Megasteam MST-513. Steamhead said that if it short cycles to downfire it. Is it as simple as that?

The past 2 days I have run a simple test: Raise the thermostat 4 degrees and see what happens. Both times, the same result - continuous burn for 30 or so minutes and the thermostat temp raises 2 or 3 degrees. The last degree was achieved over the course of 5 or 6 two minute cycles, I assume because of pressure. The pressuretrol is set at Main 1.5/Diff 0.5. The 0-30 pressure gauge must be plugged or something as it pretty much reads "0" at all times.

The other test I ran was raising the thermostat 2 degrees and it had no problems. I can say there seems to be a lot of hissing, etc. coming out of the radiators, so perhaps this goes back to my mainline air vents?

In reference to my venting, I have 2 supply mains, each of them has a Ventrite 35 at the end of the dry return (parallel flow with dry return and a hartford loop - if that makes sense?) . I recently purchased two Gorton No. 2's to replace the Ventrite main vents. All other radiator vents are working at various levels - I also purchased some Gorton No. 6's for upstairs... maybe those will help?

I ran into an unfortunate situation where my first installer made excuses and futzed around for 2 weeks trying to get my Megasteam and SuperStor installed, only to butcher it and leave us without heat for 2 days during a blizzard here in MA. That being said, we hired another company in an emergency situation who doesn't necessarily specialize in steam heat, but seemed competent enough to get the job installed per Burnhams recommended diagram (no dropped header though...). Also, the boiler hasn't been skimmed since the install was finished, it's been 2 full days now.

Anyways, where do I start and what can I have the installer do to remedy this? Any input would be greatly appreciated. If you need more info, I'll do my best to answer questions. Pics attached, let me know if you need more - Thanks!


  • Jamie HallJamie Hall Member Posts: 6,653
    The short answer...

    is yes, you may want to downfire a little.  Probably not very much; having a few cycles on pressure near the end of a recovery from setback is quite normal.  A lot depends on how fiddley you -- and your installer -- want to be about it.  You can burn a lot of installer time making a small change, seeing what happens, and then proceeding from there -- and since every time you change the firing rate, you have to readjust the whole burner...

    The hissing from the vents may well be helped by additional venting on the mains. 

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • ST140ST140 Member Posts: 41
    Downfire a little?

    What does "a little" mean? Obviously I'm not going to attempt this myself, but I'd like to have some guidelines to move forward with the installer. Is there some method of matching EDR to a new nozzle size I should mention to him?
  • David NadleDavid Nadle Member Posts: 624

    I'm loath to disagree with Jamie or Steamhead, but it seems to me if you burn for 30 minutes before you cut out you're not short cycling due to an oversized boiler. The short cycles at the end are caused by your system going to vacuum. One or more vents give way and admit air very quickly after cut-out. Then when you cut in again, everything is already hot and it takes very little time to hit pressure again. Maybe you should downfire for other reasons, but in my humble opinion, not for this reason. Do you ever hear a "whoosh" when the pressuretrol or thermostat cuts out?

    Because the boiler is new and hasn't been skimmed I believe vents are opening intermittently and hissing due to wet steam. I think your priorities should be to get the boiler and water clean, the #2s installed, and hopefully insulate the mains before anything else.
  • Jamie HallJamie Hall Member Posts: 6,653
    How I learn stuff...

    you may disagree with me anytime, David!  It's how I learn things (that, and making my own boneheaded mistakes).

    I would actually agree with you -- if the thing only starts cycling after 30 minutes or so, it can't possibly be that much oversized.  Particularly as it would appear that there may be venting problems as well.

    In answer to ST140's direct question -- I would never downfire something by more than 5% at a time, and then try it, and I'd only do it in cold weather (Charlie from WMass had an interesting post the other day on the way radiation "grows" -- demands more steam -- in cold weather so a system which is marginal in mild weather may not be adequate on a design day).  In fact, in this instance, like David I'd probably leave the thing alone and pay attention to other issues.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • ST140ST140 Member Posts: 41

    Thanks David.

    The installer only left me with a ~4" long (total) nipple/coupling/plug setup at the 1.5" skim port off the back of the boiler. I've never skimmed before, and I know there have been numerous posts on the Wall re: skimming, but would you say that this 4" setup is sufficient to skim the boiler, or should I reconfigure it somehow. If so, what should that configuration be? I assume it would involve a ball valve of some sort..

    I forgot to mention another thing besides the hissing, etc. Because of the "special situation" my first installer left us with on that blizzard day, I think the "half done" piping job he left us with pulled a lot of water up in to our radiators... They make a gurgling/sloshing water noise when the radiators start getting hot. Is there a way to fix this too? Perhaps skimming will help with this? Or do I need to detach the radiators and manually drain them out?
  • Mike KusiakMike Kusiak Member Posts: 604
    edited January 2011

    Are you planning on using a 4 degree or larger setback? If not, then the pressure cycling would be a non issue. I would tend to agree that you probably should leave the firing rate as is for now.

     Address the other problems and see how the system responds when operating as it would in normal operation. You can always fine tune the firing rate later on when yearly maintenance and cleaning is performed. 
  • PhilPhil Member Posts: 172
    similar situation here...

    I also have a MST513 installed in Central MA. The situation is that we had this installed about 3 1/2 years ago, and after lurking here for a long time, buying Dan's books, and learning how to handle things myself (installed fittings in the skim port, added Gorton #2's on the mains, and tuned the radiator venting) the whole thing was purring like a kitten. Never cycled on pressure, never made more than 2-3 oz. of pressure, and the whole house heated evenly and quietly. Everything was pretty much ideal.

    Until we decided to renovate part of the house, and took about 1/3 of the radiation off the system this Nov. Then the short cycling on pressure started (understandably), along with noisy radiator vents and noticeably increased water consumption. Cutting to the chase, I managed to convince my service folks to drop us down from a 1.1 nozzle to a 1.0 on the burner. This has completely addressed the "problems" without causing any downside that I've been able to see.

    Since you have a new install, definitely don't change anything on the boiler setup until you get the skimming done (yes, add a ball valve to that fitting, with a 90 that you can point into a pail). That will likely dry out your steam significantly and kill the gurgling in the radiators. Adding insulation to the pipes (1" fiberglass is generally a good solution) will also help with the gurgling if that persists, and get your venting setup so that it only takes ~2 minutes to get the mains filled and the main vents closed after first steam in the header. Then, if you're still having problems with noisy radiator vents, you might consider having your service guy drop the burner nozzle by one size. I would not go any more than one size though.

    Good luck!
  • ST140ST140 Member Posts: 41
    #1 - Skimming to fix the gurgling...

    So it sounds like I should definitely start by skimming... I believe the skim port is a 1 1/2" pipe currently, at the top left of the back of the boiler. Is there a ball valve that fits this, or is there a way to downsize the pipe so I can use a 3/4" ball valve? (terminology probably wrong, but I think you know what I mean...) Also, what type of ball valve? Brass?
  • David NadleDavid Nadle Member Posts: 624
    cold skim

    You can find 1-1/2" ball valves but I'd rather see you put that money into two good pipe wrenches. It's not like you'll be accessing that skim port on a weekly basis once you get the system clean. And you'd want the end capped for safety in case that valve were accidently opened, so there'll always be a cap to remove. Using the cap and replacing the teflon tape or non-hardening dope each time you cold skim should work fine. Your radiators shouldn't be storing water. Make sure they're pitched slightly towards the boiler. But all that noise you're hearing could just be the dirty boiler water.

    Unlike Jamie I generally learn things here by reading him and others and agreeing with them. But occasionally my own experience intrudes. Skimming is necessary but the problem is that it can only remove  the oils that are on the water's surface at the time of skimming, and not even all of those. Imagine coating the inside of a bottle with oil then trying to remove every trace of it by filling the bottle halfway with water, sloshing it around, and pouring it out. You'd expect to have to repeat that process many times, yes?   

    So another area where I cautiously disagree with some of the pros here is chemical assistance. My installers added sodium carbonate and returned to hot skim 3 times, and I cold skimmed for about 15 hours total over the next month. The system responded but I still had an occasional bit of hissing or gurgling on very cold days. Desperately, I turned to the dark side. I suppose all of us who imbibe have their favorite brand; mine is Hercules boiler cleaner. It's readily available and it definitely helped me. I add a pint every year.
  • ST140ST140 Member Posts: 41

    Yes, the programmable thermostat is currently set for 68 when we're in the house, and 64 when we aren't. I think I remember seeing posts about how maintaining a constant temperature is actually more efficient - is this true, or should I just use a smaller setback?
  • BobCBobC Member Posts: 4,406
    Insulate - skim - vent

    i agree with all the comments above on skimming and possible downfiring after you have been through a couple of design days to see how the system performs when stressed.

    Start by getting all of that piping insulated with 1" pipe insulation. Start at the boiler and work your way across the basement. Check the pipes with a level as you go to make sure they are pitched correctly. While doing that you could be cold skimming so you would get two things done at once. Skimming takes hours so putting up the pipe insulation would be a good use of that time.

    Install those Gorton #2's as soon as you can and then see if the steam is reaching all the radiator valves at about the same time; the checking of steam reaching the radiator valves should be done after insulating the basement steam pipes. Put a level on the radiators and make sure they are all pitched back towards the input valve so water can find it's way back to the boiler.

    All the above can be done by the home owner so your not shelling out for labor.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Mike KusiakMike Kusiak Member Posts: 604
    Effectiveness of setbacks with steam

    There is quite a bit of debate as to how much one saves with setbacks and steam. My feeling is that setbacks can save some fuel if they are reasonable and appropriate for a given system, and do not result in long periods of cycling on pressure. In your present situation, I would try using a 3 degree setback, which would probably reduce or eliminate the pressure cycling at the end of recovery.
  • Dave in QCADave in QCA Member Posts: 1,660
    My experience with setbacks

    I have found, from experience, that the setbacks that I have tried have not produced any savings.  These have been in two difference systems.  Both are cast iron radiators, but one system is steam and the other is hot water.

    The other factor in both of these circumstances may relate to building mass.  Both buildings are brick masonry construction.  The house with hot water heat has one major interior wall that is also masonry, but there is also a lot of heavy plaster, and that does contain a lot of mass.  The other building is entirely masonry and concrete.  All interior walls are solid masonry consisting of hollow tile and brick.  All exterior walls, 16" thick, are also solid masonry, and even the flooring systems are reinforced concrete and hollow tile, about 14" thick.  When you let the mass of the building cool down, it takes a lot of heat to warm it back up, and the setback was not saving anything, just changing when the boiler ran.  In normal operation it runs as needed, every hour.  When running setbacks, it runs huge amounts of time when coming out of setback.
    Dave in Quad Cities, America
    Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
    System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
    Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
  • ST140ST140 Member Posts: 41
    edited January 2011
    Cold Skimmed

    So I really wanted to skim the boiler today, so in a last minute decision, I decided to go to (I know...) Home Depot and pick up some stuff to make a proper skimming setup. After getting it setup with a ball valve and 90 degree elbow, I let it "drizzle" for about four hours. It was a little tough in the beginning getting the water level to be correct, but I think I figured it out eventually. Because the boiler was newly installed the water was still clear-ish with little dirty granules, etc. in it, and perhaps the slightest tint of reddish orange. I did this for probably about four 5 gallon buckets worth. Anyways, it seems for now at least that the sloshing/whooshing inside the radiators is gone. Thanks for the tips, and here's to hoping...

    Oh and PS - I ordered a WIKA 0-3 psi gauge from today, so I can check to see where the system is actually operating (I'm curious!). Anybody want to point me to a step by step on how to install this since my 0-30 is useless/broken and never moves from 0 even though it's brand new...
This discussion has been closed.


It looks like you're new here. If you want to get involved, click one of these buttons!