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hydronic heating

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Pinball
Pinball Member Posts: 249
in THE MAIN WALL
Another tip.

when useing a non-ferrous expansion tank, be sure to check air pressure with a gauge. Most ST-12 tanks around here come pre-charged at 40psi. Not 12psi like we're used too. it will make the relief valve blow off.

Al (pinball)

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  • Robert Gould
    Robert Gould Member Posts: 3
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    Boiler Selection

    I have an 1100 sq. ft. house and I have placed a pex tubing(non o2 barrier) system in the day light basement slab and will place tubing for the first floor joist bays. A heating contractor has proposed the Triangular Tube Prestige model as a boiler. Anyone have experience with these? How does it size up with the Polaris or other?
  • ALH_4
    ALH_4 Member Posts: 1,790
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    Thoughts

    What is your heat loss?

    The Prestige is an excellent choice. You might also look at the similarly priced Viessmann Vitodens 100 8-30.

    I would recommend oxygen barrier tube for the main floor, even with the stainless steel boiler. You're probably ok with the non-barrier tube in the slab because the concrete provides some oxygen barrier, but you need some sort of barrier in the joist bays. Also be sure to use some sort of heat transfer plate. Extruded aluminum plates are best. There are many manufacturers offering extruded plates these days. With extruded plates, you can run the concrete slab at the same fluid temperature as the upper floor.

    How will the system be controlled? In this type of situation, I am a proponent of constant-circulation, single-pump systems with zone valves and a differential pressure bypass valve. Is it all radiant? How many zones?

    For a new home that size, you should be able to get by with a single Grundfos 15-58 pump for the entire system.
  • Josh_10
    Josh_10 Member Posts: 787
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    I would also recommend using non-ferrous metals on everything.
  • Brad White
    Brad White Member Posts: 2,398
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    Given that you already installed

    non O2 barrier PEX, you should strongly consider a plate heat exchanger for that portion. As Andrew said, even with a stainless boiler. Isolate and limit the damage potential.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • Josh_10
    Josh_10 Member Posts: 787
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    That be the right way Brad ;)
  • ALH_4
    ALH_4 Member Posts: 1,790
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    Oxygen Diffusion

    Brad is probably right, I may have been a little lax in not recommending isolation of the non-barrier tube in the slab, but I have seen iron components in boilers connected to slabs with non-barrier tube that have not had significant rust after a decade of use. Though out of a slab and at higher temperatures, there is far more oxygen diffusion.

    I have seen high temperature pex in Thermofin connected to Vitogas 50's that developed tiny rust deposits at every nick in the EVOH barrier from installation. This was Roth pex installed in the late 90's and controlled by a Tekmar 252. There was no mixing valve on this system. I have attached a photo. The rust "crater" was at a small scratch in the EVOH barrier. They were visible throughout the system. It's something to think about when handling pex around concrete.

    A plate exchanger and additional circulator certainly cost less than component failure in the future due to oxygen diffusion issues.
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