Illinois Tankless Water Heating with desuperheater

Discussion in 'General Discussions' started by Henningfeld, Oct 31, 2019.

  1. Henningfeld

    Henningfeld New Member

    My domestic h/w heater started to leak last night and is going to need to be replaced. I'm pondering the idea of changing to a electric tank-less and having that fed from the 50 gallon buffer tank. I live in the Midwest where it does have a summer/winter. Is this a good plausible idea? I found some past discussion but they have been pretty dated.


    My previous home was a natural gas tankless with no desuperheater setup. It worked very well. My new residence is in a rular area with propane so I'd like to elect to do an electric tankless. Hoping to gain insight if people have had good experiences with them and this setup.

    I look forward to hearing your thoughts. Thank you for your time.
     
    Last edited: Oct 31, 2019
  2. ChrisJ

    ChrisJ Active Member Forum Leader

    I think you need to find out if the tankless will operate properly being fed warm or hot water.

    Chris
     
  3. Henningfeld

    Henningfeld New Member

    Thanks Chris, I'm assuming the unit is able to detect what temperature the water is coming in at. As that parameter fluctuates with the change of seasons with out a buffer tank.
     
  4. ChrisJ

    ChrisJ Active Member Forum Leader

    True but probably never over 70*F. I might be thinking of gas fired tankless, I know I read somewhere that high entering water temps are an issue.

    Unless you have a bunch of solar panels to off set the electric, I would get a heat pump hot water heater to go after the storage tank.
     
    Last edited: Oct 31, 2019
  5. SShaw

    SShaw New Member

    I just installed geo and was looking into this. The Stiebel Eltron Tempra Plus is supposed to work fine with the DSH and buffer tank. I also spoke with the manufacturer to confirm it would work. The Tempra Plus can handle hot incoming water and will modulate its wattage output based on the incoming water temperature. I ended up going with the DSH and keeping my conventional electric water heater for now. The added cost was a consideration, as well as the need to add two 50A circuits, and the large peak power draw. I may go tankless in the future though.
     
  6. Henningfeld

    Henningfeld New Member

    Understand, the goal is in the future to have a solar array to offset the electric usage in the home.
     
  7. Henningfeld

    Henningfeld New Member

    Thanks for the info. I talk to a local plumbing supplier they stated the same. That an electric W/H really needs to be thought about at the beginning of home construction cause electric service and panel box room. He did say for as efficient the setup already is with a DSH and another tank that the gain would be almost moot and most likely not pay for its self.
     
  8. SShaw

    SShaw New Member

    Right. I have 400A service and plenty of panel space, but the tankless cost was significant. The tankless was another $2,300 installed. Adding that to the cost of the DSH and buffer tank would bring the total cost for the HW solution to over $4,000. That seemed like a bit much for the small amount of hot water we use.
     
  9. gsmith22

    gsmith22 Member

    Couple of comments on related points being touched upon here:

    1. tank style electric hot water heaters (heat pump, element, or hybrid) are going to have a wattage of 4000 to 6000 which is 17 to 25A on a 240V circuit. Not really a deal breaker for most people's electrical service entry capacity. This is not the same as an electric instantaneous hot water heater (EIHWH) which as noted above might need 100A of breaker (real load is something less; maybe 85A? which would equate to 20kW). But using electric for instantaneous hot water will result in a huge spike in power draw nonetheless and depending on service entry size, size of home, and fixed electrical equipment in the house may necessitate an upgrade in electrical service. Think of an EIHWH as a really, really fast "sprinter".

    2. Most solar arrays installed at residences are "marathon runners." They create bulk electricity over time possibly using some/all during creation (depending on current load) or storing it either in the electric grid, a battery setup, or some combination thereof. So from the perspective of powering an EIHWH, the presence (or not) of a solar field is likely to be meaningless because they have polar opposite electric use/creation curves. You may net out even at the end of the year in use/creation (spike in draw by EIHWH balanced by long duration creation of field) but the solar field you would need for specifically powering an EIHWH as it is drawing current is going to be seriously huge.

    3. DWH with buffer tank and finishing electric or heat pump hot water heater tank is likely to be the most efficient setup from both the perspective of available hot water and reasonable cost. There are lots of threads on this forum regarding this setup so I won't rehash. If you can't be deterred from "instantaneous" then I would say use gas knowing that is probably less efficient than the DSH, buffer tank, and finishing tank.

    4. Its curious to me that panel upgrades are being discussed for an EIHWH but I never see the same discussion with respect to converting from a furnace to a geothermal heat pump that also has electric resistance heat. Depending on the size of the heat pump, you could have anywhere from 35-55A draw. Add in 5 or 10kW heat pack and you can easily be at the same overall current draw as the EIHWH discussed above. Makes me wonder if anyone is considering the service entry electrical ramifications of installing geothermal heat pumps in a heating climate.
     
  10. SShaw

    SShaw New Member

    I was going to mention that I needed to add wiring and breakers for three 240V circuits for my GSHP install (two for the 15KW heat strips and one for the unit itself). I would have needed five new circuits if I added the tankless. After removing the oil furnace and ASHP outdoor unit, I did have one unused 240V circuit and one unused 120V circuit though.
     
  11. Henningfeld

    Henningfeld New Member

    Got it, my house does have two panels so chances are I have adequate electric. The solar panels I put up would by grid-tied so the idea would be just to net close to nothing at the end of month/quarter etc.
    From what I have gathered it seems geo with buffer tank and DHW is highly efficient and in "most" cases you wont see much savings from going tank to tank-less.
     
  12. gsmith22

    gsmith22 Member

    just to clarify, circuits/breaker spaces/# of panels isn't the same as the service entry capacity. Theoretically, you could have numerous subpanels wired to your main panel and create hundreds of breaker spaces. As an example, say you have 4 - 60A subpanels (with 8 to 12 breaker spaces in each) wired into your main 200A panel with its 40 breaker spaces which would give near 100 breaker/circuit spaces. But your service entry capacity is still limited by the 200A main breaker in the main panel. What I am talking about is possibly of pulling more than your 200A main breaker can handle simply by adding 100A of load via the heat pump and heat pack. It could definitely happen in an all electric house with 200A service (ask me how I know :)). The NEC code has a method of calculating the necessary service entry capacity but there are plenty of online spreadsheets that have been developed that will do the same. It can be an eye opening experience. I doubt this would ever be an issue with 400A service but definately a possibility with all electric house on 200A or less service.
     
  13. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

Share This Page