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Suggestions wanted

bill nye_3
bill nye_3 Member Posts: 307
Suggestions wanted (or at least considered) Long story , I hooked up a wood boiler for a friend about five years ago. It is an outside boiler and I did not want to mix the water with the system water so I used an eighty gallon indirect water heater as a heat exchanger. The system was a gravity circulation system from the teens or twenties. A Burnham V34 boiler with circulators was installed in the early 1980's. The house is  not insulated and the home owner does not want to compromise the plaster or craftsman style wood trim or siding.

So, to get to the point. They do deep setback and will not change habits. When the thermostat calls for heat so much cold system water returns it causes the oil burner to start. Some other plumber rigged some hokey switch so he could shut off the burner while the wood was going. But now people are away from home and oil burner can't be switched on an off.

 My thought was to disconnect the oil boiler from the loop, tie the main together and use two closely space tees to protect the boiler from all the cold system water on a call for heat. I am probably not doing such a good job trying to explain this. I put the guy off for a year or two but now he wants me to do something next week. Every summer I put him off and fall arrives and then it is too late. 


  • Snowmelt
    Snowmelt Member Posts: 1,415
    Central boiler

    I would think some kind of aquastat has to be used when the temp goes below 140 that means no more wood in the wood boiler and the oil boiler comes on. I would use a flate plat hex instead of a full indirect water heater.
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239

    Put the system on constant circulation with ODR and put a fake thermostat on the wall.

  • Jamie Hall
    Jamie Hall Member Posts: 23,276
    I don't blame the man

    for not wanting to compromise the plaster and trim and siding and all -- I face exactly the same consideration here (although I have an additional headache -- this place is a museum, and National Register and all that -- so even if I wanted to...).

    But it couldn't be a worse setup for deep setbacks.

    Not only are gravity systems really bad at recovering from deep setbacks -- they were never meant to do that -- but the deep setbacks are, whether your client realises it or not, very hard on the plaster and woodwork.  Never mind any furniture, paintings, musical instruments (pianos, in particular, react very badly), and what have you.  But you probably can't convince him.

    I like Harvey's idea. 

    It seems to me that what is needed is to sort of reverse the thinking.  Make that oil burner your base heat -- the floor of the setback --on an ODR with constant circulation, and use the wood burner to lift the place out of the setback, or to hold it warm if and when there are people there to fire it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • bill nye_3
    bill nye_3 Member Posts: 307
    primary -secondary

     I dug out my books "to get learned up" on this stuff again. Pumping away and primary -secondary made easy. I found my notes from a Dan Holohan seminar on 8-24-05 in New London, Ct. Back before the economy fell apart.
  • hot_rod
    hot_rod Member Posts: 22,121
    P/S may not

    protect the oil boiler from cold operating conditions without a temperature sensing, and responding logic.

    What about a three way themostatic mix valve on the oil boiler? A 3 way is a simple, effective, non - electric option.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • bill nye_3
    bill nye_3 Member Posts: 307
    What I have learned

    I asked a lot of people a lot of questions , no one seemed to have an answer. Chris from Winnelson stepped up to the plate. We did a heat loss, I surveyed all of the radiators and looked them up in Dan's EDR book.  Most of the numbers seem pretty good. I used slant fin's hydronic explorer and I was a little "light" on my load. Chris redid it an fudged a few factors I wasn't aware of so worst case at 0° F it is about at 90,000 btuh. So I only need about 9gpm through the system.

    The wood boiler is about 100 feet away from the 80gallon indirect so 200 feet round trip + 50% for friction fittings and check valves you got 300x .04 = 12 ft of head + some more for the coil in the indirect. 1" pex both ways

    So the wood fired water boiler had a 3/4" tapping and a 007 pump. Today I tied three 3/4" tapping's together and put in a 0014 . The 0014 came with the boiler and I wasn't aware of it.  Tomorrow I will tie three 3/4" returns together. Easier said than done in very limited space.

    The indirect heater was circulated through the oil boiler the way it was always done. Into the return and out of the supply. I am going to pipe the heating system return into the 80 gallon indirect, just like a buffer tank, and then into the boiler return. We will see if it works. Customer "Will Not " give up tankless coils so out door reset may be hard to accomplish. I may do Honeywell that plugs into the new aquastat or a tekmar 256 .

  • Ironman
    Ironman Member Posts: 7,376
    Primary Loop

    I would connect the house piping to form a primary loop and then use two sets of closely spaced Tees to inject into it. Moving from return to supply, the first set would be from the indirect that's connected to the wood boiler. The second set would be from the oil boiler into the loop. This way the wood boiler would supply whatever heat it could and then the oil boiler would kick in if the wood boiler is not producing enough. You could use a strap on aquastat or ETC to hold the oil burner off if the wood is producing enough heat.

    I concur with HR that some form of thermal protection for the oil boiler would be prudent.

    Obviously, your biggest obstacle is your thick-skulled customer who won't listen to his pro. Setback on a gravity system is totally counter-productive. It's using more fuel and also sacrificing comfort. Not to mention the thermal stress it's imposing on the boiler.

    Another issue with ODWBs is that most are slow to recover, especially when hit with a dump load like your facing when that system comes out of setback. The more buffer that you can add to the wood boiler, the better it will handle the dump load and the more efficient it will burn.

    I like Harvey's solution best. :)
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • bill nye_3
    bill nye_3 Member Posts: 307
    Prim/sec piping

    One of my biggest obstacles and the reason I am looking for help is the piping arrangement. I can not seem to get my head around how I can tie it together. My Imagineering skills are not working well on this one. The piping leaves the boiler in two directions . Two supply and two return. The supply main decreases in size toward the end of the main. The last radiator( both sides of house ) is the end of the supply and also the beginning of the return.

    In my first post I may have stated money wasn't going to be a problem, well now it  is. The cost of plumbing supplies is crazy. $25-30 and up for one 1-1/2" or 1-1/4" copper fitting ! I will try to at least get some outdoor reset as much as the tankless coils will allow.

    Thanks for listening. If I can get a camera I will try to post a picture.
  • Zman
    Zman Member Posts: 7,569
    edited July 2014

    The way I see it you have 2 problems.

    The first problem is inadequate flow to the OWB. I agree that 9 gpm should be your target. Assuming that your indirect has fairly low resistance (not an amtrol) here is about what you will see:

    Taco 007                4.4gpm

    Taco 0014              6.63gpm

    Taco 0013              8.34gpm

    Grundfos 26-99    7.8gpm

    The other problem is the piping/control arrangement.

    Since the boilers are piped in series, when either is firing, it is wasting heat through the other. If you don't have glycol in the outdoor boiler, you may need this setup to prevent the outdoor boiler from freezing when on vacation and the OWB is not firing. If you don't need to keep the outdoor boiler warm using the indoor boiler, it would be pretty simple to install an aquastat and a DT/DT relay that would only allow the indoor boiler to fire if the outdoor boiler is cold. You would simultaneously turn on the indoor boiler and turn off the circ to the outdoor boiler. Problem solved...
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Zman
    Zman Member Posts: 7,569
    Freeze protection

    If it turns out you need freeze protection, You could have a seperate control that would turn the OWB circ back on if the water drops below 50 degrees and then off of it goes over say 70 degrees. If this was wired in parallel with the other control, it would give freeze protection without wasting as much heat or confusing the primary control into thinking the  OW boiler if firing.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • bill nye_3
    bill nye_3 Member Posts: 307
    money spent

    Personally I don't think that I would have dropped all the big coin on this outdoor woodstove and related piping. The home owner is a good friend and I got involved after everything was in place. I do not have any electrical  wires that can communicate between the two boilers. I found out today that the boiler had two 1-1/4" tapping's. I spent a lot of time manifolding the 3/4" tapping's together. But I would have had to drain 400 + gallons of water with expensive additives. So, I guess it was justified.

    I read the directions today for the first time. The wood boiler people do not want the return temperature to fall below 150° F for extended periods . So I think the 0014 @ 6.6 gpm isn't such a bad thing. It came with the boiler incase you used a shell and tube heat exchanger. Those little pumps are $$$. If I do outdoor reset I won't need high temperatures most of the season and I won't get the huge system dump load when the t-stat calls.

    I would have spent all that money on insulation , windows and doors, a good boiler , out door reset , and an indirect water heater.
  • bill nye_3
    bill nye_3 Member Posts: 307

    I will try to borrow a camera and post a picture or two.
  • SWEI
    SWEI Member Posts: 7,356
    I'm guessing that

    the 1" PEX is already buried?  Just wanted to makes sure that wasn't still an option.  I'm not a big fan of big pumps whenever I can find a way to make use of a small one.