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Tankless hot water heater in slab heating system in shop?

...I'm hoping that someone in the group has some definitive answer on this question, as I've heard all different answers to the same question. The following is my question as presented to other folks in the radiant heat field, who recommended that I post this inquiry to this forum:

...sorry to bother you, but John Vastyan at Common Ground and Merle Henkenius here in Lincoln, NE, referred me to you regarding a problem I am having with trying to find out if a heat source I had planned on using for a shop is workable. I had purchased the system through Menards, they consulted with Consolidated Plumbing's Tom Coe, we were told that our plan of using a tankless electric heat source would work, then he back tracked and said only the manufacturer of the tankless water heater could guarantee it would work, or how to hook it up, then I called CEC and got some very helpful individuals, but they told me that it could NOT work, that I would need a boiler....so, I am getting all kinds of conflicting information on what to do here. I've heard that you are an expert on these systems and if you didn't know an answer you could refer me to someone who could help me.

...in brief, it is a 40x60x16 shop, we laid durapex #10 250 runs in an 8" concrete floating slab, with 2" extruded polystyrene. It is a Chief/York Steel building with ~4 inches fiberglass insulation, has two 14x14 doors (insulated).

...We bought all the components from Menards/CPI, they sold us a propane water heater, then we decided to go all electric and changed to a 40 gallon electric water heater, but then we decided to go to a tankless electric water heater to avoid the tank. Tom Coe at CPI said that the system didn't care where the heat came from and that it would work, but now he won't assist in setting up the system and defers questions to the tankless heater supplier, and Menards is not much help. So, I'm hoping I can get some definitive direction from you on what can and can not be done here. I did talk to a local plumber, he suggested buying an electric boiler, at $5,000+...but that was about $4500 more than what we were planning on. So....help, if you can. Thanks for your consideration.


...again, would appreciate any insight any of you experts in the field could afford me.

Comments

  • hr
    hr Member Posts: 6,106
    If it has to be an electric

    heat source, I would go with a boiler designed and certified for this. i have tried various brands of electric instant heaters when the owners supplied and insisted. i have yet to get one to work.

    I like the Slant Fin wall hung electric boiler. EFM makes a lower priced, although not as nice as the cast iron slant Fin.

    Price seeem a bit high for just a boiler? Depends on the load of the building.

    Make sure you have a large enough electricial circuit to handle an electric boiler. i suspect you will need 50,000 BTU/ hr or more. The heat load calc should give you the exact load.

    hot rod

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  • DaveGateway
    DaveGateway Member Posts: 568
    Go back to LP or oil

    A small wall hung tankless water heater approved for heating like the Takagi will run you under a grand. A small oil fired HW tank should cost under 2 grand.
  • Dave Heath_2
    Dave Heath_2 Member Posts: 52
    Tankless Electric heater

    A heat load would be required to properly size the heat source. You mentioned that you looked at a electric 40 gallon tank as the heat source. The problem you have is they come with 4500 watt element and that is just not large enough to heat a 40 x 60 shop. How many KW is the Tankless electric heater?

    You mentioned you have already purchased all the other components. What would they be? Are you using a CPI prebuilt radiant panel?



  • marc
    marc Member Posts: 203
    i agree

    > heat source, I would go with a boiler designed

    > and certified for this. i have tried various

    > brands of electric instant heaters when the

    > owners supplied and insisted. i have yet to get

    > one to work.

    >

    > I like the Slant Fin wall hung

    > electric boiler. EFM makes a lower priced,

    > although not as nice as the cast iron slant

    > Fin.

    >

    > Price seeem a bit high for just a boiler?

    > Depends on the load of the building.

    >

    > Make sure

    > you have a large enough electricial circuit to

    > handle an electric boiler. i suspect you will

    > need 50,000 BTU/ hr or more. The heat load calc

    > should give you the exact load.

    >

    > hot rod

    >

    > _A

    > HREF="http://www.heatinghelp.com/getListed.cfm?id=

    > 144&Step=30"_To Learn More About This

    > Professional, Click Here to Visit Their Ad in

    > "Find A Professional"_/A_



  • marc
    marc Member Posts: 203
    i agree

    with you hot rod, slant fin is a great electric boiler, very reliable, quiet, and very efficient. up here in the northwest some areas are paying less than 3 cents per kw.

    as far as using a on demand hot water maker for space heating, i would think that this extremely shorten the life span on the unit. the few we have worked on or installed, have not stood the test of time, and there is nothing worse than that call on the weekend asking why didnt you tell me this would not last. installing reliable equipment for their intended use tends to lower the service calls. marc
  • Dof3
    Dof3 Member Posts: 120
    No luck with electric

    Would a Bosch 38 be enough for your job? If you could use gas. Or aren't they good for infloor heat?
  • DaveGateway
    DaveGateway Member Posts: 568
    Bosch 38

    Be aware that install instructions on mnay tankless water heaters like the BOSCH spell out in bold lettering "NOT APPROVED FOR SPACE HEATING PURPOSES" so no warranty if you use it for heating. WH's are great for radiant (both tank and tankless) but use approved models.
  • Dof3
    Dof3 Member Posts: 120
    Joe Brix

    Thank you for the info on the Bosch WH. I will check to see if they are approved.
  • Mike C_2
    Mike C_2 Member Posts: 2
    Electric Boilers

    I worked for a company that sold and installed electric boilers that were manufactured by Seisco. We sold hundreds of them. They work flawlessly providing that the system was designed correctly. Someone mentioned earlier, that you should have a heat calc done. I agree. I have found that the largest error encountered from DYI was not placing enough tubing in the slab. This always seems to be the one place that they like to cut cost. The one down fall of using an electric boiler is as someone else mentioned is having a large enough service to serve the AMP load of the new boiler. Remember that you can only use 60% of the panels total capacity. Most of the times this means bringing in a new service panel just to service the boiler. As far as I'm cocerned BTU output either from a electric or gas boiler is BTU output. If you don't have enough tube in the floor or no under slab or perimeter insulation you'll have problems no matter what unit you use. Best of Luck

    Mike
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