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Dual fuel electric boiler...or?

Hello,

I recently purchased a home in rural Colorado that has a four zone in-floor radiant system with an NTI Trinity T200 propane boiler. Two weeks ago, I had a large grid-tied solar PV array installed with the goal to power the entire house (including DHW and hydronics).

To this end, I have installed an electric heat pump hot water heater and am looking to add an electric boiler. My goal is to run the electric boiler most of the time but to keep the Trinity in-line as a back-up or for those times when my solar production is not high enough to power the electric boiler (ie. when it is cheaper to run on propane than electricity).

I had originally considered the Stiebel Eltron Hydroshark 3 for its initial economy, but in reading posts on this forum, am now under the impression that it might be better to go for a boiler with an outdoor temperature sensor.

My question is, what would you recommend as the best boiler for my system?

Ideally, I am looking for a boiler that I can hook directly into the system without having to modify the system too much.

System specs:
1) 3300 sf house with a design loss of around 50,000BTU/hr at the local design temperature.
2) Four zone hydronic system. Generally only use two zones - main floor and master bedroom (1/2" pex in gypcrete). Sometimes heat basement which is on third zone (pex in main slab-basement stays around 55* year-round without heat), never use fourth zone which is the garage and entry path to home.
3) NTI Trinity T200 propane boiler, Taco 0011-F4 circulator, Taco SR 504 relay, Grundfos UPS 15-42F pump on each zone.

I am happy to post pictures of the system if that would help. I appreciate your time and expertise.

Thank you.

Andrew

Comments

  • RobG
    RobG Member Posts: 1,850
    Look at the Thermolic boilers. They are a good product and have outdoor reset. Post some pic of the system and we can see how best to tie it in.

    http://www.thermolec.com/en/productView.aspx?type=product&id=58
  • SWEI
    SWEI Member Posts: 7,356
    Second that recommendation for the Thermolec. A B-15 would handle the entire calculated load, but do you really need that if a significant portion of the space is infrequently occupied?
  • RobG
    RobG Member Posts: 1,850
    edited December 2014
    Why did you put in such a large propane boiler? Even in low-fire it is 1/3 oversized. The Lochnivar WHN055 would have been a much better fit and much less money.
  • Redfish
    Redfish Member Posts: 4
    Thanks for the replies and the suggestion to check out the Thermolec.

    We will likely size the electric boiler for the whole house even though we don't currently heat the whole house. This, because we are a young and growing family and also for resale purposes.

    The NTI came with the house. I have often wondered the same thing, as it seems completely over-sized.

    I have attached a few photos of the system. My thought is to tie-in the electric boiler to the right of the NTI and have both boilers in parallel (the Thermolec Installation Manual has a clear diagram of this orientation). I figure I will have to reposition the Taco circulation pump so it is upstream of both the electric and gas boilers on the return circuit (see images).

    Any other installation tips, tricks, or must-knows?

    Thanks,

    Andrew

    PS. How do the Electro Midsize dual fuel boilers compare in quality and economy to the Thermolec?

    image

    image

    image
  • RobG
    RobG Member Posts: 1,850
    Wow! That is some funky piping. I would re-pipe it as primary-secondary while installing the electric boiler. While you are at it how about replacing the NTI with a correctly sized unit and put the NTI up on Craigslist.
  • SWEI
    SWEI Member Posts: 7,356
    edited December 2014
    The T200 uses a high head loss HX, definitely need primary/secondary there along with a careful evaluation of the existing pump sizes. Again, might want to consider replacing it wiht a properly-sized boiler.

    Given the nearly nonexistent head loss of the Thermolec, it can simply be piped in series with the secondary loop.
  • Redfish
    Redfish Member Posts: 4
    Thank you, gentlemen.

    As I am relatively new to radiant systems, are there resources (articles, drawings, documents) you can point me to for more information on primary/secondary plumbing as well as evaluating system head loss for sizing pumps properly?

    Also, any thoughts on the Electro EB-MO series boilers?

    I appreciate your time and expertise.

    Andrew
  • RobG
    RobG Member Posts: 1,850
    Why are you stuck on the Electro? It doesn't look like it has OAR (I have never used one). I have used the Thermolic without issues. If you are looking for radiant heating resources you are in the right place. If you go to the "store" there are many books that will be of interest. Just wander around the site and chances are you will find what you are looking for. If you can't find it just ask here!
  • Redfish
    Redfish Member Posts: 4
    edited December 2014
    Electro and Primary/Secondary Loop drawings

    The Electro caught my eye because it is comparably priced to the Thermolec, has dual fuel and OAR, and carries a 20 year warranty. I am certainly not sold on it, but am interested in hearing from anyone who has experience with these boilers, especially relative to the Thermolec.

    I have included several system drawings below. The first outlines the current plumbing. Then there are two outlining a couple of different primary/secondary options based on a few articles that I have looked at. The second two drawings are overviews only and don't include system specifics (pressure relief valve, expansion tank, etc).

    I am interested in feedback on whether these two options are viable; if not, why not, and if so, which one is preferable to the other (barring the cost of a hydraulic separator).

    Thanks,

    Andrew




  • SWEI
    SWEI Member Posts: 7,356
    Unlike the rest of the Electro line, the EB-MO is basically a direct competitor to the Thermolec. Thermolec has a stainless pressure vessel as standard equipment and comes in a wider range of sizes.