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How badly over-sized is my boiler? Can I down-fire?

I calculated my radiator square footage at 499. My boiler specifications sticker (Peerless 63-06-sprk/wis) shows a net rating of 745 net square feet steam. This is a 10-year-old gas boiler on a one-pipe parallel flow steam system in an 80-year-old 3,500 square foot brick two-story house.

If I multiply my radiators' 499 square footage by 240 BTU I get 119,760. Boiler sticker shows net steam of 179,000. How badly over-sized am I? Almost precisely 50% oversized? Anybody know if this boiler can be down-fired or retrofitted with a hi/lo burner?

After the boiler has been off 45 minutes to an hour, with thermostat set at a constant 68 and outdoor temperature around 40 with minimal wind, when the boiler fires, I get steam at the vents on the shorter of my two mains 7 minutes after start-up of the boiler flame. Steam hits the vents at the end of the longer main precisely 3 minutes later. My new 0 to 3 psi gauge shows somewhere between 1 ounce and 2 ounces of steam pressure when the two mains' vents get steam and close. The boiler continues to fire another 7 minutes and the pressure gradually climbs until the boiler shuts off at 33 ounces of pressure (despite my presuretrol being set at 0.5 and 1, that is where the flame shuts off every time on pressure).

I have 3 Big Mouths on my longer main and a Gorton #1 and a Big Mouth on the shorter main, and by my calculation they have more venting capacity than their 3/4 inch antler can carry, so I am vented as well as I can get. All radiators have new Maid-o-Mist vents, they are balanced pretty well, and I have shimmed them for correct return condensate pitch. Radiators are completely silent. I also now get ZERO water hammer in the 60-foot section of my main that leaves the basement and runs (fully insulated) through a crawl space, after many hours of torture in my crawl space installing clevis hangers and gradually tweaking pipe slope for good condensate return. Before adjusting the pitch of that section of main I had a moderate amount of water hammer. I have also flushed my wet returns by threading in an NPT/hose thread adapter nipple and running garden hose water through the wet returns. I was quite surprised that almost no corruption flushed out. I expected to see the horrors of the ages cleaning itself out of those wet returns. Site glass level barely moves up and down when boiler is firing, and the water level returns to precisely the boiler-off height within a couple minutes after the boiler has stopped firing.

How am I doing?

I figure if I installed a vapor stat and set it to much lower pressure, I would get a lot of short or short-ish cycling until the thermostat satisfied. Would those on/off cycles be a beneficial gas savings, or would the system-off cycles be offset by inefficiencies caused by stop/start and wear and tear on the system? Should I leave well enough alone with my pressuretrol and forget about getting a vaporstat?

Comments

  • BobC
    BobC Member Posts: 5,473
    That boiler is oversized by more than 50%. To heat all the radiators fully the boiler sq ft of steam should match the connected EDR. The sq ft of steam has a hidden 33% pickup factor to handle piping losses so that boiler can supply twice the EDR you have IF there were zero piping losses.

    How many times does the boiler cycle on a normal call for heat? Take some pictures of the boiler and the boiler header, if the piping is optimum you can offset some of the problems caused by an oversized boiler. Dialing down to a very low pressure will just make short cycling worse. Depending on the boiler it might be possible to downfire it somewhat.

    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Abracadabra
    Abracadabra Member Posts: 1,948
    edited February 2017
    49% oversized

    that boiler comes with a vr8304 which is a on/off single stage valve.
    replacing the valve with an appropriate 2 stage valve may be possible, but you'd be modifying the gas train and that creates issues. you would also obviously need to do a proper combustion analysis.

    if your boiler is shutting off at 33 oz. and you have the pressuretrol set to 1psi main, there's a problem. What type of pressuretrol?
  • EzzyT
    EzzyT Member Posts: 1,292
    You can stage fire the boiler with a 2 stage gas valve and a vaporstat.
  • Motorapido
    Motorapido Member Posts: 307
    I don't use the thermostat set back feature, and cycles on warmer days are usually one on cycle from cold to full 33 ounces of pressure, then that cycle shuts off on pressure and often that satisfies the stat. On much colder days I get one long on cycle, off at 33 ounces, back on when pressure drops to 8 ounces and then one more back up to 33. If really really cold, three cycles.
  • Motorapido
    Motorapido Member Posts: 307
    My piping seems good according to Dan's books
  • Motorapido
    Motorapido Member Posts: 307
    edited February 2017
    Here are the pipes
  • Motorapido
    Motorapido Member Posts: 307

    49% oversized

    that boiler comes with a vr8304 which is a on/off single stage valve.
    replacing the valve with an appropriate 2 stage valve may be possible, but you'd be modifying the gas train and that creates issues. you would also obviously need to do a proper combustion analysis.

    if your boiler is shutting off at 33 oz. and you have the pressuretrol set to 1psi main, there's a problem. What type of pressuretrol?

    It's the standard, garden variety Honeywell. Looks like it was new 10 years ago when the boiler was installed. Pigtail is completely clean. 0 to 3 psi gauge is installed on a brass T with the gauge on one side of the T and the Pressuretrol on the other side of the T. The little pin hole in the pressuretrol seems to be clean. Both adjustments are set as low as they can go, with the screw-actuated slider down as far as it will go just before the screw pops out of the threads. The wheel is set at 1 where the wheel will not turn any more. Theoretically, it should shut off at 1 psi, but it is shutting of at 2 psi and one ounce. That is not too bad for these not-too-accurate devices, right?
  • Motorapido
    Motorapido Member Posts: 307
    If I inquire with Peerless, would they be able to provide the specifications that a decent gas technician could use to set it up for two-stage?
  • Fred
    Fred Member Posts: 8,542
    The Pressuretrol probably needs to be recalibrated but @ 33 ounces, that only just over 2 PSI. Not the best but marginally OK. If you can get a 2 stage gas valve installed and a combustion test done, it would work out well for you and really help to keep your pressure down well below 2 PSI.
  • BobC
    BobC Member Posts: 5,473
    I can't really tell what is going on with your boiler header but it almost looks like you are taking steam the header between the two steam outlets of the boiler. Are the steam risers full size coming out of the boiler and is the header a full size bigger?

    Going to two stage firing would be better but if the boiler does not short cycle during normal operation you might be spending a good deal of money for an improvement that will take a long time to pay back. The same would go for replacing the near boiler piping if it's not optimum.

    If it's not broke . . .

    Bob

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Motorapido
    Motorapido Member Posts: 307
    BobC said:

    I can't really tell what is going on with your boiler header but it almost looks like you are taking steam the header between the two steam outlets of the boiler. Are the steam risers full size coming out of the boiler and is the header a full size bigger?

    Going to two stage firing would be better but if the boiler does not short cycle during normal operation you might be spending a good deal of money for an improvement that will take a long time to pay back. The same would go for replacing the near boiler piping if it's not optimum.

    If it's not broke . . .

    Bob

    What's a wild guesstimate on paying a pro to install a two-stage burner? Meanwhile I will measure my two pipes off the boiler and measure the header pipe diameter and post that info along with more pics.
  • Abracadabra
    Abracadabra Member Posts: 1,948



    What's a wild guesstimate on paying a pro to install a two-stage burner? Meanwhile I will measure my two pipes off the boiler and measure the header pipe diameter and post that info along with more pics.

    You're not going to get a price for that work here.
  • Motorapido
    Motorapido Member Posts: 307
    Fred said:

    The Pressuretrol probably needs to be recalibrated but @ 33 ounces, that only just over 2 PSI. Not the best but marginally OK. If you can get a 2 stage gas valve installed and a combustion test done, it would work out well for you and really help to keep your pressure down well below 2 PSI.

    Do I understand correctly that all the extra pressure I am creating is not adding to my heating speed, but instead is just burning up gas unnecessarily while the system waits for the pressuretrol to shut down the burner?
  • Motorapido
    Motorapido Member Posts: 307



    What's a wild guesstimate on paying a pro to install a two-stage burner? Meanwhile I will measure my two pipes off the boiler and measure the header pipe diameter and post that info along with more pics.

    You're not going to get a price for that work here.
    Oops. I've done it again. I suppose I am not asking for anybody to quote, but instead for somebody to just wild guess it, but I suppose that runs afoul of the no-price-talk law. Sorry about that. I respect forum rules. This was an honest mistake.
  • Fred
    Fred Member Posts: 8,542
    That boiler piping is not right. Look at the picture in the owner's manual for correct piping.
    Here is the procedure to re-calibrate the Pressuretrol if you feel comfortable doing it or if you want to have someone do it for you:
    Inside the Pressuretrol, right below the micro switch, there is a pivot arm. At the end of that arm you will see a screw pin that is activated by the diaphragm at the bottom of the Pressuretrol. If you look very carefully at that screw pin, you will see it actually has a tiny (I mean tiny) hex head on it. It takes a .050 hex wrench and you can turn it clockwise (Towards the bottom of the Pressuretrol to decrease the Cut-out pressure or counter clockwise to increase the cut-out pressure (which none of us want to do but who knows, your Pressuretrol may be really screwed up!). Turn the power to the unit off first. You may find the first attempt to turn that screw a little bit stubborn (relatively speaking) because it has some Locktite on it but it does turn. Don't turn too much, a fraction of a turn goes a long way towards getting it adjusted where you want it (maybe 1/32 inch turn to start with). You may need to play with it to get it exactly where you want cut out to be.
  • Jamie Hall
    Jamie Hall Member Posts: 22,956

    Fred said:

    The Pressuretrol probably needs to be recalibrated but @ 33 ounces, that only just over 2 PSI. Not the best but marginally OK. If you can get a 2 stage gas valve installed and a combustion test done, it would work out well for you and really help to keep your pressure down well below 2 PSI.

    Do I understand correctly that all the extra pressure I am creating is not adding to my heating speed, but instead is just burning up gas unnecessarily while the system waits for the pressuretrol to shut down the burner?
    You got it... but vaporstats aren't all that cheap, so... as @BobC said, it may not be worth the money.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Motorapido
    Motorapido Member Posts: 307
    Fred said:

    That boiler piping is not right. Look at the picture in the owner's manual for correct piping.

    Good to know.

    How bad does my boiler piping appear to be, and would it be a major investment to pay a true steam pro to set it up according to manufacturer specs? (note that I am not asking for price, but just asking if it would be the type of investment that would make me burst into tears, or a more modest investment that would likely pay off in the foreseeable future with lower gas bills)

  • Motorapido
    Motorapido Member Posts: 307
    The two pipes that rise off the boiler measure 2.4 inches diameter and they join a central pipe that measures 3 (close as I can measure due to inability to fully pull back insulation. Steam main is 3 inches, too. Here are two more pics.



  • Motorapido
    Motorapido Member Posts: 307
    The two pipes rising out of the top of the boiler appear to be connected to a reducing bushing. Why the heck did the installer not use full-size piping to match the size of the main? What kind of false economy was that? The uninsulated pipe that runs back horizontal to the left rear of the boiler is also 2.4 inches, while the central vertical pipe and the main measure 3 inches.
  • Fred
    Fred Member Posts: 8,542
    Where are you? If one of the Pros on here is in your area, they may be able to look at the system and give you a quote. Will it save you on gas bills? That's not the point. There is a minimum standard that each boiler manufacturer requires for their boiler to run properly and for their warranty to remain intact.

    You picture looks like the risers out of the boiler may be bushed down, there is no Header, the equalizer should drop off of the end of the header and I can't see what the wet returns look like or if there is a Hartford loop. You really need a set of skilled eyes, on site, if at all possible.
  • Motorapido
    Motorapido Member Posts: 307
    Harrisburg, Pennsylvania -- the intellectual capital of the northeast and home to many beautiful women. ;-)
    WayneMech
  • Motorapido
    Motorapido Member Posts: 307
    Fred said:

    Where are you? If one of the Pros on here is in your area, they may be able to look at the system and give you a quote. Will it save you on gas bills? That's not the point. There is a minimum standard that each boiler manufacturer requires for their boiler to run properly and for their warranty to remain intact.

    You picture looks like the risers out of the boiler may be bushed down, there is no Header, the equalizer should drop off of the end of the header and I can't see what the wet returns look like or if there is a Hartford loop. You really need a set of skilled eyes, on site, if at all possible.

    Here's the best pic I can get for now of the wet return, the water make-up inlet and the return pipe to the boiler.
  • Motorapido
    Motorapido Member Posts: 307
    pipe that is vertical, running up to noon on the photo is a pipe that then turns horizontal, travels across the top of the boiler, then rises to meet the 3 inch pipe that is the vertical pipe to which the two pipes coming out of the boiler join to. Skinny copper pipe is fresh water. It joins the end of the wet return, just before the wet return drops down to the pipe with the condensate drain valve, which has a riser up to the pipe that then goes back into the boiler.
  • Fred
    Fred Member Posts: 8,542
    That looks Ok. Only one Main or is there a second main that has been tee'd in somewhere past that pipe that rises up on the top of the boiler?
  • EzzyT
    EzzyT Member Posts: 1,292
    First I would tackle the near boiler piping with a sizable header to add some mass to the system and then move to the stage firing.
  • KC_Jones
    KC_Jones Member Posts: 5,707
    @Steamhead might go to Harrisburg. I'm just a little south from you in Hanover, PA, but I'm just a homeowner.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • Motorapido
    Motorapido Member Posts: 307
    Fred said:

    That looks Ok. Only one Main or is there a second main that has been tee'd in somewhere past that pipe that rises up on the top of the boiler?

    ,
    Only one main out of the boiler room. In about 70 feet, a riser comes off it to feed a 2 inch branch main that travels 60 feet to feed 4 radiators, and then that branch terminates in a wet return. The remainder of the main that continues after the branch comes off it is 27 feet, and then that main drops to a wet return.
    KC_Jones said:

    @Steamhead might go to Harrisburg. I'm just a little south from you in Hanover, PA, but I'm just a homeowner.

    KC Jones you better watch that speed (Grateful Dead lyric, of course), and apropos to steam discussions, riding that train, which was certainly a steam engine train.
  • Motorapido
    Motorapido Member Posts: 307
    KC_Jones said:

    @Steamhead might go to Harrisburg. I'm just a little south from you in Hanover, PA, but I'm just a homeowner.

    KC, if as a highly advanced amateur homeowner you believe you have gained the skills to assess systems and suggest improvements, consider driving up to Harrisburg, check out my boiler, and my wife and I will buy you a steak dinner. You seem to really know your stuff.
  • rick in Alaska
    rick in Alaska Member Posts: 1,457
    I don't know if Harvey Ramer does steam, but unless I have my geography wrong, he is close by.
    Rick