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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
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
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Comments
http://www.thermolec.com/en/productView.aspx?type=product&id=58
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?
Given the nearly nonexistent head loss of the Thermolec, it can simply be piped in series with the secondary loop.
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
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