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Neep help W/ expansion

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by longboarder2, Nov 19, 2012.

  1. longboarder2

    longboarder2 New Member

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    so thanks to everyone on the forum who have helped me in fine-tuning my wood/oil boiler to work together and not burn down my house. recently with my new wood burning strategy, i am having another small problem---

    i am burning wood in the early to late morning--getting the house up to temp, letting the fire burn out (trying not to idle), then heating from late afternoon until midnight or so. i have been doing so with the air door always open, but adjusting the intake similarly to a conventional wood stove.

    the problem i have been having is the blow-off on the wood boiler has been popping more frequently. granted, i am burning wide open and not allowing it to idle, but my temps have not been outrageous (two incidents so far--one @ 200 andf one @ close to 220) i would expect the boiler pressure to spike during those high temp mishaps, but it's also doing it during regular heating. we are heating a lot of water and have plenty of places for the heat to go. most of the time, the boiler pressure hovers around 12lbs, but i see it creeping up into the 20's more often lately--even when i turn some zones up to get rid of some of the temp.

    on the top of the oil boiler, i have an extrol tank and a spirovent. on the wood boiler, just a maid of the mist.

    a friend of mine who spent many years doing heating up in Mass. recommended another expansion tank on the top of the wood boiler, with a taller (12") riser (currently only about 4 inches off the top of the boiler) and an air scoop.

    any recommendations??

    btw: prior to my pyrotechnic event last winter, this was occurring on the oil boiler. now it's isolated to the wood appliance---i do not want to keep blowing off and bringing mineral-rich water into the system

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  2. lotawood

    lotawood Member

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    What boiler do you have? Idle capabilities and temp that idle occurs? Any aqua stat?

    I got no idle or aqua stat, but I do have storage and over temp shut down and a big expansion tank.
  3. avc8130

    avc8130 Minister of Fire

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    I will bet money you need more expansion tank capacity. I am having the same issue with my new Wood Gun install. What size tank do you currently have? I had a #30 Extrol (4.4 gallon) on my install and my boiler would over-pressure. I have a #90 (14 gallon) on order.

    ac
  4. maple1

    maple1 Minister of Fire

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    What is a 'maid of the mist'?

    Air scoops are good. Not sure on the taller riser thing. Bladder expansion tanks can go almost anywhere - you might just be able to T one in where your 'main of the mist' thing is plumbed in at. Not getting a clear idea of what you have now - pics always help. As far as how much expansion you need, that depends how much water is in your system. 15% should be pretty safe.
  5. stee6043

    stee6043 Minister of Fire

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    To really know how much exapansion you should have you need to estimate how much water you have in your system. For what it's worth you should very rarely, if every, pop your pressure releif. It is not typical for a properly setup system to hit 30psi.

    Some use a rule of thumb of 5% system capacity for expansion. I've got more than that to allow for potential future expansion.

    And last, why are you hitting 220 with your boiler?? 200 isn't such a big deal once in a while but 220 is getting up there on the "should I be concerned" meter. It sounds like you have some system issues to look into.
  6. maple1

    maple1 Minister of Fire

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    Likely because his air door is always open. I don't think that's the best way to run a conventional boiler with no storage.

    OP, do you have a dump zone? Guessing no if you're seeing temps that high - if no that would be even riskier. I think I'd be looking to make some changes.
  7. Bob Rohr

    Bob Rohr Minister of Fire

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    Assume your system holds 60 gallons of water. Runs from 60°F to 180° it would need 4.3 gallons of expansion. If you run it up to 220°F you need almost twice the expansion capacity. Calculate the volume and size the expansion tank, or add expansion tank capacity until the pressure increase stays below 25 psi or so.

    Attached Files:

  8. longboarder2

    longboarder2 New Member

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    thanks for the replies: been late getting to check them out.

    i do have a dump zone---slant fin baseboard heating 100 sq. ft. of finished bsmnt.---works great; always colder than the rest of the house, no thermostat, has maintained the boiler safely a few times.

    im using a harmon sf160.

    the boiler only got over 200 twice, for very short amounts of time. once i forgot to turn on the circulators and aquastat switches at startup.. the other was when the main circulator was not working---had to turn impeller manually and got everything flowin'. both times, the temp spikes were 10 minuters or less.

    the air door stays open because i do not want the stove to idle. i build smaller fires now and leaving the intake open has not presented an issue as there is plenty of demand for heat.

    i guess i will need to calculate how much water i am using and place another extrol on top of the wood unit. any opinions on the air scoop on that? i figured having a spirovent in the system would be enough.
  9. longboarder2

    longboarder2 New Member

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    bob, thanks for the diagrams. unfortunately, i'm not sure how much water is currently in the system. i do know that when i am just heating with the oil boiler, the extrol tank on the top is perfectly sized because i have never had an issue and the pressure stays down around 10-12 lbs, never seen it over 20.

    the wood boiler has a 25 gal. water capacity and the dump zone consists of 32' of slant fin baseboard fed by about 80 or so ft. of 3/4" copper.

    based on those numbers, how large of an extrol should i put on the wood boiler.

    i have noticed that when i heat with wood for a longer period of time and the house temps remain more consistent (rather than up and down) the pressure stays sub-20.
    unfortunately, it's never really cold enough for long enough to just keep burning wood here.
  10. avc8130

    avc8130 Minister of Fire

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    Are your wood boiler and oil boiler plumbed together?

    How big is the Extrol on the oil boiler?

    If your pressure is exceeding 30psi(the blowoff) you need more expansion.

    ac
  11. longboarder2

    longboarder2 New Member

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    they are plumbed together---the wood boiler pulls water from the return of the oil burner and blows it into the supply side of the oil boiler. Extrol model number 30. pre-charge pressure 12psi.

    its driving me nuts---i have increased the intake air to raise the flue temp, now my pressure is staying up around 25 and dribbling out of the blowoff. going to be warm later in the week so the wood appliance will be off. thinking about adding the same size extrol on the wood boiler as well.

    just when i thought i had this f'n thing figured out!? wtf?! i know im close, just missing a small detail somewhere.---not enough guys around this area doing this stuff, so im doing a lot of reading and a lot of guessing.
  12. maple1

    maple1 Minister of Fire

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    I thought it was already decided that you needed more expansion - so did you add expansion yet?
  13. avc8130

    avc8130 Minister of Fire

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    Relax. Calm down. Take a breath. This is easy, I promise.

    You need more expansion tank capacity. You added a wood boiler, along with associated plumbing. This increased the water capacity of your system. You need to add expansion to match.

    Now, you PROBABLY could get away with adding another 30...but it isn't tough to figure out before you start spending money.

    From my calculations, you have added ~30-35 gallons of water to the system capacity (25 in the wood boiler, ~2 in your dump zone, plus additional piping).

    Assuming your 30 was sufficient for your old install, you could PROBABLY install another 30 and be ok. You could DEFINITELY install a 60 ALONG with your 30 and be ok.

    OR

    You MIGHT be able to REPLACE your current 30 with a 90. If it will fit in your current location, it would be as simple as valving off the system and unscrewing the old and screwing in the new.

    Without pictures and specs it is very difficult to make an accurate assessment of your system, however, you CAN work through this.

    Trust me, I did last week. LOL

    [​IMG]

    [​IMG]

    ac
  14. longboarder2

    longboarder2 New Member

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    i already decided to go with hanging another 30 off a scoop on the wood boiler. i'll be burning tonight and tomorrow am. after that, were looking at five or so days of mild weather--going to add the expansion tank and see what ahppens when i fire back up. thanks for the info avc! will post after the addition w/ the results.
  15. avc8130

    avc8130 Minister of Fire

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    I don't mean to be a jerk, but another 30 might not be enough. It might be close. I have heard the rule of thumb is 15% of system capacity. If you added ~30-35 gallons, you would need another 4.5-5.25 gallons. The 30 only holds 4.4. Will it work? MAYBE. With what you have told us about your system, I would ADD a 60 or REPLACE the existing 30 with a 90 if it will fit.

    Replacing the 30 with a 90 is REALLY easy if it fits. No real plumbing, no additional parts. It literally took me 10 mins.

    ac
  16. longboarder2

    longboarder2 New Member

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    i can dig it. i dont have room down there for the 90. i have room up on the wood appliance for a 30 definitely and a 60 possibly. in the case of these extrol tanks, is it impossible to have too much room. thats to say if the 60 fits, but i dont need it--will having too much exp. capacity cause any performance problems?
  17. avc8130

    avc8130 Minister of Fire

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    Absolutely nothing wrong with too much expansion other than it costing you an extra $30.

    ac
  18. maple1

    maple1 Minister of Fire

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    Better safe than sorry.
  19. longboarder2

    longboarder2 New Member

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    the $30 i have. it's the patience i lack. i will bolt on the 60. hopefully after this gets fixed, i can address my flue temp----

    it's amazing; when i first started reading about wood boilers about four years ago, it seemed like a pretty easy "set it and forget it" deal. not the case.
  20. avc8130

    avc8130 Minister of Fire

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    Did you read about wood boilers on this forum? "set it and forget it" is about the last impression anyone could get from more than 5 mins around these parts...

    Running a wood boiler is a hobby. A hobby that actually has the nice side effect of keeping your family warm and happy.

    ac
  21. Fred61

    Fred61 Minister of Fire

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    After five years, I'm pretty much at the "set it and forget it" stage. Up until this year, the first order of business every morning was check the storage temperature. Now I don't even look at it 'til 11:00 AM or so if I check it at all.
  22. maple1

    maple1 Minister of Fire

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    I've only been at gassing & storage not quite a couple months yet. I don't think I'll ever stop frequently checking things, especially when I get up in the morning - but I'm at least now up to the point of being able to take time to make sure I'm fully awake & to use the bathroom first. It was a cold & windy -12c this morning when I woke up to a warm house, I was sure my storage would be down & I'd need to burn earlier than I have been, but it was still 180 at the top when I checked at 7:30. After 17 years with my old one, and struggling to keep the house warm with it on wood, I have now concluded that my house is tighter than I thought it was and my old unit was putting out less heat than I thought it was. I wish I had found this place way sooner than I did. It's been a steep short rushed learning curve, but man was it worth it.
  23. EffectaBoilerUser (USA)

    EffectaBoilerUser (USA) Member

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    Certainly sounds like you need more storage.

    With the proper sized expansion tank your system should not go over 20-25 psi when the system is at its hottest temps.
  24. Bob Rohr

    Bob Rohr Minister of Fire

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    \
    Not to confuse the choice but the tank can be mounted anywhere in the room, tee it into the same spot and use pex, copper, steel pipe, what have you, to pipe to the location you mount it. I have seen them installed on their side in a joist space, lying on the floor, strapped to the side of boilers, many options.

    Quick and easy would be 2 Sharkbite adapters, one 1/2 FIP on the tank, one- MIP at the connection tee, and a few feet of pex tube.
  25. longboarder2

    longboarder2 New Member

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    the only thing i am a little on the fence about is wether to just hang it on a 't' or hang it off an air scoop---been hearing a few opinions about both. i have a spirovent and #30 extrol on the oil boiler; wondering if the scoop is overkill or would complicate/lessen performance.

    supply house down the road wants $100 for the 60 extrol--thought that was a bit steep.

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