Waterfurnace and Hotwater questions
Page 1 of 2 12 LastLast
Results 1 to 13 of 19
  1. #1

    Waterfurnace and Hotwater questions

    I am building a new home and just had a system analysis completed for my house they spec'd a 4 ton unit for the house and it looks great but I had some questions on the desuperheater and the most efficient way for hot water. What I am considering is using a 50gal Electric HWH as a holding tank and use an LP Tankless HWH after the Electric HWH.

    Or I could use a LPHWH and use a Electric Tankless that way in an event of a prolonged power outage I could fire up the LPHWH and still have Hot water

    Opinions and suggestions are very appreciated.

    Jason

  2. #2
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,829
    Except during prolonged operation, you won't really create enough hot water to satisfy your needs using the desuperheater alone. So your suggestion to use a holding tank and a gas fired tankless water heater make good sense. I would use a similar system if designing it myself. You'll need the gas unit during the shoulder seasons when you're not running the heat pump at all or very little.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  3. #3
    good to know I am on the right track, anyone else have a different suggestion and why it would be better?

  4. #4
    Join Date
    Jun 2001
    Location
    DFW
    Posts
    684
    For your electric tank, look into the Marathon brand.

    I'm using the 85 gallon model for the holding tank for my heat pump water heater and the combination is working very wel.

  5. #5
    Join Date
    Feb 2008
    Location
    ga.
    Posts
    85
    You will actually use desuperheater in cooling and heating. Water furnace also give you the option to shut it off with the flip of a switch. Personally I would use the electric water heater as the holding tank and L.P. as primary tank.
    Definition of insanity is to do the same thing over and over expecting a different result.

  6. #6
    Does brand really matter for my holding tank since I will not be running any electric to it?

    Quote Originally Posted by paul42 View Post
    For your electric tank, look into the Marathon brand.

    I'm using the 85 gallon model for the holding tank for my heat pump water heater and the combination is working very well.

  7. #7
    That's basically what I am thinking except except I will be using a tankless L.P. heater after the EHWH which will not be hooked up to electric.

    That is unless I am misunderstanding what you are saying.

    Quote Originally Posted by krriffle View Post
    You will actually use desuperheater in cooling and heating. Water furnace also give you the option to shut it off with the flip of a switch. Personally I would use the electric water heater as the holding tank and L.P. as primary tank.

  8. #8
    Join Date
    Jun 2001
    Location
    DFW
    Posts
    684
    Quote Originally Posted by jhartbarger View Post
    Does brand really matter for my holding tank since I will not be running any electric to it?
    The Marathon is guaranteed to never leak.

  9. #9
    excellent good to know! thanks for the tip.

    Quote Originally Posted by paul42 View Post
    The Marathon is guaranteed to never leak.

  10. #10
    Join Date
    Mar 2007
    Location
    Connecticut
    Posts
    104
    Quote Originally Posted by jhartbarger View Post
    That's basically what I am thinking except except I will be using a tankless L.P. heater after the EHWH which will not be hooked up to electric.

    That is unless I am misunderstanding what you are saying.
    First, the Marathon tank is a great tank, and the configuration you are considering is the correct way.

    I am not one to suggest cheap, but what you want to do is just connect the desuperheater water circuit to a hot water storage tank. It can be any insulated vessel (with pressure relief). I would recommend a regular electric tank for this, and don't bother wiring it. This holding tank will then feed your Tankless water heater.

    You can get most of your summer water this way, and a good portion of the winter, but little to none in shoulder seasons.

    Your tankless water heater has a built-in water temperature sensor, so it will modulate its firing rate depending on the entering water temperature from the holding tank.

    I would caution you on using a regular 85% efficient model - get one of the new condensing models (92% AFUE or better) - yes about $1,000 more. The regular 85% efficient units can suffer from a lot of condensation rolling back down the flue because of short run-times in this configuration - so make sure the vent pipe is drained correctly. I've actually seen the gas valves flooded full of water because of this!

    Good luck.

  11. #11
    Quote Originally Posted by Buck_Taylor View Post
    First, the Marathon tank is a great tank, and the configuration you are considering is the correct way.

    I am not one to suggest cheap, but what you want to do is just connect the desuperheater water circuit to a hot water storage tank. It can be any insulated vessel (with pressure relief). I would recommend a regular electric tank for this, and don't bother wiring it. This holding tank will then feed your Tankless water heater.

    You can get most of your summer water this way, and a good portion of the winter, but little to none in shoulder seasons.

    Your tankless water heater has a built-in water temperature sensor, so it will modulate its firing rate depending on the entering water temperature from the holding tank.

    I would caution you on using a regular 85% efficient model - get one of the new condensing models (92% AFUE or better) - yes about $1,000 more. The regular 85% efficient units can suffer from a lot of condensation rolling back down the flue because of short run-times in this configuration - so make sure the vent pipe is drained correctly. I've actually seen the gas valves flooded full of water because of this!

    Good luck.
    Do you have a particular Tankless in mind that is one of the new condensing models? Only one I found so far is a Bosch Pro

  12. #12
    Join Date
    Mar 2008
    Posts
    21
    I have a Rinnai tankless and am getting ready to hook up the DSH. I am going with the Marathon 85 as storage to feed the tankless. The tankless is great but the DSH has never been used as I was uneducated when I built. The heat is just going to waste so it is time to use it. I just hope the water into the tankless is not to warm to cause problems...

  13. #13
    Join Date
    Mar 2007
    Location
    Connecticut
    Posts
    104
    Quote Originally Posted by jhartbarger View Post
    Do you have a particular Tankless in mind that is one of the new condensing models? Only one I found so far is a Bosch Pro
    Noritz, Takagi and Rannai all make excellent units. Noritz is the larget manufacturere and is releasing a new > 92% efficient unit soon (if not already). Takagi already has a condensing unit out (has for over a year). I have not received any announcements from Rannai, but I'm sure they have one coming out soon too.

    I've got a Bosch at my house, it is OK, but not as easy to service. I've had some condensing issues with this unit, and had to service the thing several times and modify the installation to overcome some of its design shortcomings, but is still a decent unit. This unit is over 5 years old, so one of the first generation units - hopefully they've made a few improvements (the components are fine).

    Quote Originally Posted by firefly
    I have a Rinnai tankless and am getting ready to hook up the DSH. I am going with the Marathon 85 as storage to feed the tankless. The tankless is great but the DSH has never been used as I was uneducated when I built. The heat is just going to waste so it is time to use it. I just hope the water into the tankless is not to warm to cause problems...
    These systems have internal water temperature sensors. Yu pick the output water temperture during setup. The units modulate their firing rate to deliver this temperature based on water flow rate and entering watering temperature. If the entering water temeprature is alreeady 100 deg F, then it will only add 20 degrees. The problem is because this is such a low firing rate, you will get condensation in the exhaust pipe (at least in colder climates) that you need to make sure is drained properly. This is why I recommend a higher efficiency condensing unit. The high-efficiency units are designed to deal with condesnate much better than the typical 85% effient units.

    If you use solar or a desuperheater tank and the water is already over 120 deg F, then the unit shouldn't fire at all! This makes it a very efficient and convenient system.

    Please post back on your experiences. Thanks!

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event