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Combi wood /gas with large storage tank question

clammyclammy Member Posts: 1,996
I have a question on a combination wood /gas  burner hot water boiler .I understand that with type of set up the buffer is used for storage when the wood is the heat source .But when the gas side is operating should there be a three or four way valve to by pass the storage tank being there is no reason to heat it due to there is no storage needed due to the burner operating only on a call for heat and it's aquastat.The main corcern being the cost of maintaining the large buffer tank using a gas gun being the HO has never even turned the gas side on ever and has strickly burned wood for like 12 years.I was told that it does have some piping issues and that the original installation company had to re pipe a few times due to some issue .I was also told the boiler was imported from sweeden i will be looking at it next week .I gather the guy is getting tried of burner wood and wants the luxury of the gas so they an get away from being a slave to the flame .Thanks for any input and advie.peace n good luck clammy


  • IronmanIronman Member Posts: 3,542
    More Info


    A little more info would help. Where is the buffer tank located and how well is it insulated? If it's in the house where any heat loss from it would go into the structure, then I can't see much value in the expense of a bypass and re-piping. If it's outside, then would it be exposed to the point that freezing would be an issue?

    I'm not familiar with the particular piece of equipment you're dealing with. Is it an outdoor wood stove? If it's an indoor, then the method Ive used is to put in a large enough indirect tank and pipe the coil in it on the return to the wood boiler. The domestic storage then indirectly becomes the buffer for the wood boiler. Use a tank with an electric heat element and it will supply domestic in the summer when the wood boiler is not fired. Of course, you'll need a tempering valve and an aquastat to hold the pump off so the electric element doesn't heat the wood stove.

    There are other approaches, but would need to know the particulars of you job.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • clammyclammy Member Posts: 1,996
    a little bit more info i think?

    Thanks for the reply as far as i have been told it is a indoor unit ,wood fired with a aux gas gun hot water boiler  .It is not like a tarm unit being it does not hold a large quanity of water .I was told that there ia a very large storage tank there they are using for storage being they have only used it burning wood .I was also told there where no bypasses or 3 valve ways between the boiler and the storage and until i see it i believe they are pulling heat out of the buffer ,my thoughts are that when you are burning inexpensive wood (getting it for free) it's no big deal keeping the storage tank warm but if you are paying for the gas it ain't so good .As for the storage tank my buddy states it is huge volume some where maybe in 1000 gallons indoor in a sub basement .Depending on what i see i would believe that if the system pulls off the storage tank to heat the home then this guy can except a pretty large gas bill .I was told the whole house is cast iron baseboard and about 2500 to 3000 sq ft . I am going there this tues to finish the wiring and set up the gas gun depending upon what i see .As i stated in the first post this unit was imported from sweden and was installed about 12 years ago the gas set up came with the unit but was aside from the gas line  hook up it was never  wired orput into service .I was wondering if what  i am stating makes  any sense .I know i would rather have my gas burner working off my indoor thermostat rather then trying to maintain 160 or 180 temp in a 1000 gallon storage tanks .What's your thoughts .Peae n good luck clammy
  • hot rodhot rod Member Posts: 7,080
    a number of ways to pipe

    parallel or primary secondary would allow you to run the boilers separate or together. With wood it is nice to be able to bypass the storage to cover the load as quickly as possible. A 3 way zone valve could do that for you.

    I don't think you would ever heat the buffer with the gas boiler, that should go to the load directly, unless it is grossly over sized and short cycling.

    This is how I have my wood boiler and buffer piped currently. The 50 gallon ThermoCon tank acts as a separator, a bit of buffer and some air elimination. This feeds to a HTP Solar Phoenix tank that acts as a back up when the ThermoCon drops below 100F.

    Here is a great article that shows a number of options for piping and control wiring from Siggy.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • clammyclammy Member Posts: 1,996
    Thanks Hot Rod

    Thanks Hot Rod for the informational article.I believe from what i was told that he has a large pressurized storage tank and the boiler is a combination unit with the ability to burn wood or gas it is  a all in one type boiler .i will no more on tues day wheni get a look see .Thanks again  great artile peace and good luck clammy
  • clammyclammy Member Posts: 1,996
    Here's the skinny

    Well the wood/gas set up is  a tarn 2200 set up we set up the gas gun and had it running properly and did use a CA to dial it in correctly.The HO and a plumber had piped it but from the diagrams from tarn where not even closely followed i guess some cannot follow simple  piping diagrams .I went through it with the HO but he really does not understandand no matter how i tryed to explain it he does not get it but does kinda realize it's not totally correct when he gets his first gas bill i kinda think he will be calling or unwiring the gas gun and contiune to load wood  ,There was a large buffer tank with copper coils installed except none of it is piped right being even though he is constantly dumping heat into the tank he is not even using it domistic pre heat capacity due to the domestic water is not piped correctly nor did he install any type of mixing valve  both he and the other plumber though that he did not have one before so why do i need it now.The guy is on a first name base with the tarn guys and they have told him it is not correct and the guy just states yeah yeah but it works he did install the mixing valve on the return to keep the return water temp up but it is piped completly wrong.As far as i know it was another carrot and the donkey theme i did the set up (C A ) to help my buddy pro bona and i can see that i probalbly just wasted my time and gas and will get nothing out of it in the long run oh well it's nice to see how badly some things can be done and still manage to get a passing inspetion sticker with no backflow ,prv or low water cut off or dump load .No wonder i some times feel i should get into another line of work being any idiot can do what i do exept they don't want to spend 2 grand for a CA so they might as well use that carrot to there advantage .Nother one bites the dust peace and good luck clammy
  • rainmakerrainmaker Member Posts: 20
    thanks for the idea

    HR posts good stuff so I borrowed some info to inspire my current project:

    (please comment there if you have any advice?)
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