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Little bit of help with final hookup

Darko Member Posts: 3
Hello everybody,

I was wondering if I can get a help doing a final radiant hook up on my workshop. I have spent days looking and reading different things but things are getting a little bit overwhelming and too technical.

I live in North Carolina. I have a 1400 ft.² workshop with 2 x 6 walls 12 feet tall, spray foam insulation.
The floor is 5 inches of concrete which is thermally separated from the outside with the two inch Styrofoam insulation. There is approximately 2000 feet of half-inch PEX roughly 8 to 9 inches apart split into eight separate runs of roughly 250 feet each.

I have made a drawing of my system layout and all the parts I need to finalize this but I am not clear how do I connect heat only thermostat, in slab sensor and outdoor reset.

So my question would be

1.What heat only thermostat should I get?

2.Should that thermostat have capability to connect both slab sensor and outdoor reset?

3.Do I really need both sensors? Is one better versus the other? Which one?

Any guidance on this would be greatly appreciated.

This is the list of all the components I'm getting

ECO 18 | 18kW Electric Tankless Water Heater

3/4" Sweat, Spirovent Jr Air Eliminator

Extrol #15 Expansion Tank (2.0 Gal Volume)

UPS15-58FC 3-Speed Circulator Pump w/ IFC, 1/25 HP, 115V

3/4" NPT Threaded Purge & Fill Ball Valve w/ Hose Drains

3/4" Pressure Relief Valve 30 psi (Lead-Free)

3/4" Threaded Y-Strainer, Cast Bronze, with Plug (Lead-Free)

60 Amp 240-Volt Non-Fuse Metallic AC Disconnect

8-branch Stainless Steel Radiant Heat Manifold Set w/ 1/2" PEX adapters

Taco SR501 Single zone switching relay

I have attached the pictures of my radiant heat piping and the drawing of a layout


  • Zman
    Zman Member Posts: 7,569
    That is a nice simple setup you have.
    I think outdoor reset is a must as is indoor temp feedback. From there you should either have full control over the water temp or have a slab sensor.

    The water heater temp sensor will help you limit the max water temp as will the shear mass of the slab.

    I would look into the Tekmar 552 http://tekmarcontrols.com/products/zoning/552.html
    It looks like it can handle an Outdoor, slab and indoor temp sensor. I would call tech support or a local rep to be sure as sometimes you can only use 2 out of 3 sensors.

    I assume you plan to wire the t stat to the pump relay and let the flow switch in the water heater turn on the heat.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Darko
    Darko Member Posts: 3

    Thank you very much for your quick response.
    I just went over the installation manual and that thermostat is exactly what I'm looking for. I'm going to get the 070 sensor for the outdoors and 079 sensor for the slab. Thank you very much for the suggestion, there is so much stuff available online I was getting lost. I will find my local rep and give them the call to.

    Yes, I'm going to wire the thermostat in my Taco SR501 Single zone switching relay.

    I have a one more question for you.

    On the website you gave me, the slab sensor 079 has a wire that is only 10 feet long.
    When I originally ran my PEXwill piping I ran one piece of pipe from the middle of the slab to the wall which is approximately 12 feet. If I slide that sensor inside that pipe to reach the middle of my slab I'm going to be 2 feet short plus from the bottom of the wall to where the thermostat is there is another three or 4 feet.
    Does that mean that I can slide that sensor only as far as I can reach it but still be able to connect at the thermostat or in my allowed to splice that wire and have that sensor be 15 or 20 foot long piece of wire?
  • SWEI
    SWEI Member Posts: 7,356
    For electric resistance heat, I would ditch the tankless water heater and buy a real electric boiler. A Thermolec B-18 or an Electro EB-MO-20 would give you onboard "good enough" ODR control, be covered under warranty for the intended application, and quite likely reduce your total system cost.
  • Ironman
    Ironman Member Posts: 7,373
    What's the head for the tankless heater? I seriously doubt that a 15-58 circ will be able to properly maintain flow through that + your floor loops.

    Like SWEI said, an electric boiler would be the right tool for the job.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Zman
    Zman Member Posts: 7,569
    Sensors are sensors, as long as the have the same rating.
    Either add onto the one you have or find another compatible one.
    Listen to what these guys are saying and check the resistance of the water heater.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Big-D
    Big-D Member Posts: 21
    Check out www.nextgenboiler.com. Personally I believe your 18kW tankless is vastly oversized for the sq.ft. and where your place is located. Have you performed a heatloss? The guys on here are right- get a boiler not a water heater!
  • Darko
    Darko Member Posts: 3
    Hello everybody, thank you very much for your help.

    I do not know much about radiant heat, however I know enough to install the piping buy the other things I need and put everything together. I did not do a heat calculation because I don't know how to do it and some software that I happen to see online was very expensive and quite technical.
    I have spent the last year reading and watching hundreds of videos of other people doing the same thing with on-demand hot water heater. This company eco-smart on their website lists some of some of their on-demand hot water heaters compatible with radiant heat.

    I did looked up some of the electric boilers that you have listed here and I managed to find a price for one which was almost $2000. Eco-smart 18 can be purchased on Amazon for $350.

    If I am understanding correctly the election boiler keeps the water at the much higher temperature than the instant hot water heater and requires primary and secondary loop, what would be a reason that I need that?

    If I am understanding this correctly eco-smart 18 is what the website lists modulating hot water heater.
    So let's say it's winter and I am just starting my radiant heat for the first time, the temperature of the water is let's say 50, goes through a hot water heater gets heated to 120 and let's say one hour later the return temperature is up to 60 gets heated to a 120 and another hour later the temperature is 70, as time goes by concrete gets warmer and a hot water heater draws less electricity because it needs less power to bring the water from cold to hot at some point that temperature difference should be about 20°.
    When I called the technical support this is what the guy explained this to me and this is what I found mostly online.

    This is what I found online as far as temperature difference versus gallons per minute on ecosmart 18

    Temperature Rise for ECO 18 * 123 degrees at 1.0 GPM * 61 degrees at 2.0 GPM * 48 degrees at 3.0 GPM * 31 degrees at 4.0 GPM * 25 degrees at 5.0 GPM * 21 degrees at 6.0 GPM Specification ECO 18 * Voltage 240 * Phase Single * KW 18 kW * Elements 2 x 9 KW @ 240 V * Amperage Draw 75 Amps * Required Breaker 2 x 40 DP * Required Wire 2 x 8 AWG * Electrical Panel 150 Amps * HZ 50/60 * Pipes fittings 3/4 NPT * Dimensions (in.) 18 x 14 x 3.75 * Weight 11.25 lbs. * Exchanger Copper * Activation flow .25 GPM * Energy Efficiency 99.8 % * Certification: UL/CSA

    Is there a simple way of figuring out what pump size would I need to push water through the whole circle. I have approximately 2000 feet of half-inch PEX which is basically eight different runs 250 feet each to go in a single manifold just like the picture shows. Does the pump really has to work that hard? It's not pushing through a 2000 feet of pipe it's only pushing to a 250 feet but the gallons per minute gets divided by a different runs?

    Is any of these makes sense or what am I missing?

  • Ironman
    Ironman Member Posts: 7,373
    An on demand water heater is NOT designed, controlled or ASME approved for space heating. That's why we advise people not to be fooled by Internet peddlers who try to sell these in place of boilers.

    Reason with me for a moment: we have no vested interest in what you purchase. We don't get paid by this site. Most of us are hydronic contractors, designers and installers. People come here almost weekly posting about the issues they have with a radiant system that was done according to some online merchant's hype. We see in the field the same kind of things. Our desire is to see it done right and people be happy with the radiant system that they invested in. The online peddler has a vested interest and he's well aware that by appealing to everyone's desire to get something cheaper, he can easily get folks to purchase his wares.

    "Let the buyer beware!" You get what you pay for in life.

    If an on-demand water heater could take the place of a boiler, there would be no need to make boilers.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • KC_Jones
    KC_Jones Member Posts: 5,736
    Darko said:

    I did not do a heat calculation because I don't know how to do it and some software that I happen to see online was very expensive and quite technical.

    Not really any good way to do what you want without the heatloss. It is the first thing that drives everything to come after. How much tube, how much flow, how big a boiler etc. Without the heatloss no one can really answer your questions effectively.

    I will also add to what has been said, a water heater is for showers a boiler is to heat your house/building. It's pretty much that simple, anyone that says otherwise is most likely just trying to take your money.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • SWEI
    SWEI Member Posts: 7,356
    edited December 2016
    Darko said:

    If I am understanding correctly the electric boiler keeps the water at the much higher temperature than the instant hot water heater and requires primary and secondary loop

    Incorrect on both counts. An ODR-controlled electric boiler heats the water to the temperature required to offset the building losses at the current outdoor air temperature. An electric boiler will have essentially zero head loss, so you can size the pump for just the tubing losses.
    eco-smart 18 is what the website lists modulating hot water heater.
    That means it modulates to maintain the setpoint. It does not modify the setpoint dynamically, which is pretty much the only way one can tame the thermal mass of a concrete slab full of tubing.

    Are you sure you actually need 18 kW (61,416 BTU/hr)? Thermolec's TMB series comes in sizes up to 11 kW (37,532 BTU/hr) and is (AFAIK) the most affordable ODR-controlled electric boiler you can get in North America. PM me if you need pricing.
  • Hilly
    Hilly Member Posts: 427
    The last Dettson installed was nice. More affordable than other brands and super compact. Slant/Fins are nice too, but they were more cost with their tekmar controls onboard.