Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

New Boiler and Radiant system setup questions.

marcomjl Member Posts: 8
Hi, I have an Attack DPX35 Profi gassification boiler. I have done research and read/utilizing the Modern Hydronic Heating book as my reference (awesome book highly recommend!). I am currently setting up and installing the system and boiler. I am looking for others input so comments and questions are all welcome.

I did my own sizing the system for heat loads and head.

House is a 1848 historical cape. Basement (boiler/ storage) has insulated walls and concrete floor, 1st floor has been remodeled (insulated walls and air barrier installed), and 2nd floor is not insulated currently awaiting remodel after boiler is setup for 1st floor heating. 2nd floor heating will be setup after remodel.

Boiler is an Attack DPX35 Profi gassifier.
Storage is 450-500 gallons open buffer tank with suspended separate coils I am fabricating.
System is radiant floor 1/2" pex-al 8" OC through heat transfer plates, insulated below for 1st floor. (2nd flr will be above floor with heat plates.) Loops range from 180-240' in length.
4 zones. 1st floor 4 port manifold, 2nd floor 5 port manifold, 3rd and 4th zone will be by themselves 1st flr bathroom and 2nd flr bathroom respectively.
Taco zone valves and controller pushed by a vt2218 taco pump and mixing valve, air scoop.
This is a closed circuit heat exchanger coil suspended in tank.

Boiler heating circuit has a mixing valve to control boiler return water temp at a min 140 (went with a taco 5004 mixing valve instead of the danfos vtc511 unless someone has a reason why I shouldn't). Pump is a 007 taco with a 4900 air seperator.

1. For the aftercooling circuit/Dump zone on the boiler to prevent overheating, the manufacture recommends installing a Watts Thermal Safety Valve sts20 to a water line, then to the cooling ports and exit out into I assume a drain. I have heard of many others ideas such as dumping into an existing zone, battery backup, or separate heat exchanger/ dump into storage. I don't like any other those ideas for several reasons and I want something that can actually take care of my boilers full output in case something catastrophic were to occur. With the manufactures recommendation on the water line in and dumping it out, when the thermo valve closes after opening up during overheating, doesn't the water in the cooling circuit remain? If so does it just boil/steam out and leave the cooling circuit empty again?

2. Any one have a alternative to the Watts STS20 thermo valve?

3. For my boiler heating circuit heat exchanger coil, I was thinking of 1" copper coil I would fab up into a suspended coil. I want to keep cost down and haven't found any prebuilt ones that were cost effective. I was thinking of 30' of coil, not sure if that is enough?

4. I haven't been able to find any issues but my boilers CH ports are 2" in size. Going down to 1" from that wont cause any issues? I assume this is normal?

5. On my second floor, the farthest away loop is also the largest run somewhere around 380' if manifold for it is in basement. I was thinking of the 2nd flr manifold on the 2nd flr to reduce the leads for the loops. I was thinking of spliting this loop into two loops but then a bigger manifold, double the longest leads in the entire system it would cost more, double the lead lines I'd have to chase, etc. The manifold relocated this should save me 32' minimum per loop on the other 4 2nd flr runs. To control and adjust flow between the manifolds in different locations I heard globe valves work good? Any ideas and what took look out for with remote manifolds? (I was going to insulate the main lines to and from the manifold. I do have a space in the hall at the top of stairs to have access to it also.)

6. I would like to add a 3rd coil to the storage tank to preheat and take most of the work my electric water heater does currently. Any simple solutions anyone has? I would assume I would need a mixing valve to control the output since the tank will be 140-180 compared to the water heaters 120-130 output?


  • Zman
    Zman Member Posts: 7,569
    I don't have much to add on the heat dump. It sounds like you have done your research and it is down to personal preference.

    I would caution you to take a hard look at all your mixing valves. Many are designed for domestic systems and have very high CV values. This can be detrimental to pumping efficiency.

    The coils, like any heat exchanger comes down to flow rates, temp differential and surface area. Would need all your design data (and more than one beer) to take a crack at that one.

    The size of the ports and piping all comes down to how many BTUs you are trying to move at what delta t with which circ .
    If your boiler outputs 100,000 BTU's and you want a 20 degree delta, you would be looking at 10 GPM. You can probably do that with 1". Check your math and keep in mind pex has a much smaller inside area than copper.

    I would definitely do remote manifolds and avoid long tubing runs. I would use balancing valves, either on the branches or at the manifolds if you need them. If you are careful in your pipe sizing you may not.

    A reverse indirect for domestic would be a fine idea. As would a mixing valve to keep you from frying someone. Siggy has done a bunch of those.

    Sounds like a great project!
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • daveHA33
    daveHA33 Member Posts: 1
    Automag zone valves are normally open and works well for dump zones
  • marcomjl
    marcomjl Member Posts: 8
    daveHA33 : Those Automag's require a power source? I am concerned if I lose power, I have no backup, etc.

    Zman: I only have one mixing valve planned before the vt2218 pump. I have work to do on the heat exchangers. Thanks, I'll look into a reverse indirect.
  • psb75
    psb75 Member Posts: 833
    Yes. The Automag requires power...to close. If power goes out...it opens (normally). That is the whole point of using it on the dump zone of a solid fuel heating system...like yours.
  • marcomjl
    marcomjl Member Posts: 8
    Ahh ok, thank you. Didn't look to far into them. It's still cheaper for me to just set it up like the manufacture suggest and works.
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    Can't believe I missed this one!
    I own and operate a DPX45.

    If you have any questions please let me know.

    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!