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Wood Boiler Piping

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Hey everyone, does anyone have any experience installing wood boilers? I'm installing a new Autonom, from Canada/Turkey and there is no piping diagram. The Rep recommended a mixing valve to prevent thermal shock, I figured primary/secondary piping would be better. Thoughts? 2nd question, where the heated water from the wood boiler, through the buffer tank, ties into the gas boiler piping, do I need a 3 way valve there, or will 2 pumps serve the same purpose? Thanks in advance. I'll have a better diagram to post when I get a better handle on this, I'm sure I'll have more questions too.

Thanks, Bob Gagnon

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  • hot_rod
    hot_rod Member Posts: 22,472
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    Is the gas boiler a cast iron or mod con, it will determine how best to tie the two together.

    Here are the options to protect the wood boiler if it is connecting to a buffer or a high mass cast iron radiator system.

    Either a variable speed set point circ or a thermostatic mix valve works best. The variable speed pump needs to connect like this to hydraulically disconnect the load from the boiler fig 7-15c.

    What size is the wood boiler. The 281 ThermoBloc has a small Wilo Star 16, good for 8- 10 gpm, so an 8- 10 gpm flow maybe a 100- 120K boiler, fig 6-13.

    The 280 protection valve is a 14 Cv so good for larger boilers 180- 200K max.., fig 6-7

    Tell us more about the system, BTU/hr load, type of radiation, type of gas boiler.

    You probably don't need or want the gas boiler to heat the buffer, so tie it in downstream of the buffer tank.

    Do you want a control that automatically switches the gas boiler on when the wood boiler dies down? A solar delta T controller is the best way to toggle between the two boilers.

    Idronics 10 has piping and control wiring diagram

    ams for various options.

    a

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Tom_133
    Tom_133 Member Posts: 891
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    We have installed a lot of them, mostly Frolings. The pic that Hot rod is showing with the thermostatic loading valve is what we do. We use ASME buffer tanks sets of 300 or 400 gallons, we build a box and spray foam the tanks in. It's amazing how happy the boilers and customers are with this arrangement. The price… thats another thing, those tanks aren't cheap

    Tom
    Montpelier Vt
  • psb75
    psb75 Member Posts: 863
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    The buffer tank(s) have to match the max. mbtuh of the wood boiler. Something that also needs to be mentioned is a "grid-down overheat protection" (or "heat dump zone") that is mandatory on a system with a cord-wood burner. There is probably a schematic for that in Caleffi's "Idronics" series.

  • hot_rod
    hot_rod Member Posts: 22,472
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    One rule of thumb is the buffer has the capacity to take a 1/2 firebox burn.

    Although if you are starting with a hot buffer, you may still need a dump zone. A passive dump with a N.O. zone valve is wise in the event of a power outage

    There are a few options for passive and active dump loops. Ideally any dump could go to an indirect or somewhere to utilize that energy.

    Gasification boilers can ramp their output down quickly. As long as the firebox door is closed and sealed tightly 😯

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • psb75
    psb75 Member Posts: 863
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    Thanks HR. Yes I forgot that most modern cordwood burners are now gasification. But….there are a lot of "off market" non-gas. burners still out there. I have one. A Buderus three-pass, "up" burner and it has a passive N.O. -valved "dump zone" with two, old-fashioned cast iron radiators above it. Modern Austrian-made pellet boilers also seem to be fairly safe in a grid-down scenario due to their regular use of a blower and the relatively small burn-pot with an electric auger-feed.

    hot_rod
  • Bob Gagnon plumbing and heating
    Bob Gagnon plumbing and heating Member Posts: 1,368
    edited June 26
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    Thank everyone, I'm getting a handle on this now, the first picture here is how the old wood boiler was hooked up, the 2nd picture is my proposed piping for the new wood boiler. Feel free to make any corrections or suggestions. Good to see you're still hanging around here Hot Rod.

    The gas boiler is cast iron. There are 4 zones of baseboard, 1 zone of Radiant, 1 zone for domestic.

    Looks like the dump zone is properly piped with an NO valve installed.

    I'm guessing the btu's needed for the home are 60,000'80,000, this older home is a little over 2,500 Sq ft.

    Are these the best ports to hookup the buffer tank?

    The manufacturer though a 3 way valve might be needed, to prevent the gas boiler from heating the buffer tank, I'm not sure I need that.

    The third picture is a thermostatic mixing valve, we have a rebuild kit for that.

    Thank in advance, Bob Gagnon

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  • hot_rod
    hot_rod Member Posts: 22,472
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    Yeah, I've used those Themovar valves in the past. They seem to be a Euro type NPT :), hard to seal that connection. looks like all 3 have leaked at some point. Get new fiber washers for the unions also.

    You don't want the wood boiler and gas boiler in series, fig 6-11,as the gas boiler loses some of it's output to the wood boiler and its flue. An unfired boiler becomes a cooling tower! The gas boiler should go directly to the load header.

    I don't see how you are mixing down the radiant zone? A 3 way off the header is fine.

    Pipe the two boilers parallel to the load, here are a couple examples. Fig 6-13 shows parallel, with a mod con con, it can be a cast boiler. A cast boiler does not need a circ, the zones circs will flow it adequately and we don't want it flowing into the buffer.

    And a chicken scratch drawing, if the boilers are arranged in the room with the buffer in the middle. Layout in the room is not important, just the piping method.

    These pages from Idronics 10, system 3, show how to use a delta T control to run the two boilers. A delta T control has two sensor inputs so it can watch two temperatures and decide when the gas boiler goes on or off line. I like the Resol BS plus, a tekmar 150 will work but doesn't have the nice display and VS pump functions that the Resol does. The wiring is with a plate HX for DHW just use that relay to call on the DHW circ.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Bob Gagnon plumbing and heating
    Bob Gagnon plumbing and heating Member Posts: 1,368
    edited June 27
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    Thanks so much Hot Rod, I really appreciate it. I think I have it down, but rewrote it to match the configuration here. Does this look right? Two more questions, is the one pump on the boiler return for the wood boiler all I need for that boiler? And does the dirt separator have to be on the return near the gas boiler, or could it be built into one of the Spirovents?…

    Thanks again, Bob Gagnon

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  • hot_rod
    hot_rod Member Posts: 22,472
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    Yes the wood boiler only needs that one circ. It flows through the protection valve and buffer only.

    A check valve at the tank

    A 1-1/4 or larger zone valve above the gas boiler. It's closed when the buffer is hot enough, wood boiler running, 160F or more?

    When the wood boiler is off, and buffer is cold, ZV opens the end switch fires the gas boiler. The check keeps the gas boiler from going through the tank, all gas boiler output gos to the zone circs.

    The delta T control sensor 1 near top of buffer

    What is the total gpm load? The 1-1/4 Caleffi Z-one ZV is good for 8 gpm.

    How low SWT can you supply? If you can go 140 or below you could add a mixing valve controlled by and ODR control. That would allow you to pull the buffer down much lower, perhaps.

    But adds another valve and control. 7-4 shows the loads pulled off through a mix valve, typically a radiant system, where the tank could be pulled down to 100F maybe. So the tank runs a very wide delta 100- 180F!

    We have a new 683 motorized ball valve that would handle the flow 1- 2" sizes.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Bob Gagnon plumbing and heating
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    Thanks Hot Rod, I can't seem to locate that 1 1/4" zone valve you mentioned. Do you have a model number or manufacturer? The customer is on vacation for a month, I'll finish piping it like you said when he gets back, and let you know.

    Thanks again, Bob Gagnon

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  • hot_rod
    hot_rod Member Posts: 22,472
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    Here are the part numbers for the motorized ball valves. These are power open, power close, so you need a RIB relay to operate it.

    Belimo may have some spring return versions.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream