Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.

If you've found help here, check back in to let us know how everything worked out.
It's a great way to thank those who helped you.
Need to contact us? Visit https://heatinghelp.com/contact-us/.

DHW mixing two undersized heating sources

CBRobCBRob Member Posts: 173
edited May 13 in THE MAIN WALL
You guys have been a great help with all my off the wall questions.

next one....
Can you mix a tankless DHW source (like a tri tube combi) with a standard nat gas 50 gallon water heater.

I'm trying to squeeze a snowmelt boiler into limited space, Owner could give up one of his 2 50 gallon water heaters and make room for a wall mounted Tri Tube Combi.

Could you efficiently piggy back these 2 different dhw heat styles?

If they could work together to heat DHW what order would you put them in?

thanks

Comments

  • GroundUpGroundUp Member Posts: 962
    Well sure, but why? Are there 13 people in the house or why is the DHW demand so large that a single tank or tankless couldn't do the job?
  • You could pipe them in series with the on-demand first.
    Often wrong, never in doubt.

    Click here to learn more about this contractor.
  • hot_rodhot_rod Member Posts: 13,207
    Is there a recirc involved?

    I would put the tank first to pre heat to the tankless, run the tankless at the desired temperature. Or crank to 140F and use a mix valve. That would give you legionella protection
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • CBRobCBRob Member Posts: 173
    > @GroundUp said:
    > Well sure, but why? Are there 13 people in the house or why is the DHW demand so large that a single tank or tankless couldn't do the job?


    It's a ski vacation home, 3 full baths and very cold supply water in the winter.
    Potentially could have have lots of people at the same time.
    GroundUp
  • CBRobCBRob Member Posts: 173
    > @hot_rod said:
    > Is there a recirc involved?
    >
    > I would put the tank first to pre heat to the tankless, run the tankless at the desired temperature. Or crank to 140F and use a mix valve. That would give you legionella protection

    Yep, we have a recirculation pump.

    With a mixing valve, would you run the tank first, mix it down to a lower temp and then through the tankless to desired temp?
  • hot_rodhot_rod Member Posts: 13,207
    I'd start with the demand pattern. Do they need a lot of gpm all at once? Dump loads like large tub fills? Consistent use patterns? Since they have had two 50 gallon I suspect they have a high DHW use?

    If so the combi would need to be able to cover the loads based on the temperature from the first tank, the delta T it works against based on required gpm and supply temperature, say 115F.

    It is somewhat common to see solar DHW tanks upstream of tankless heaters in Europe. Caleffi has a thermostatic valve assembly that selects between the two DHW sources. Use the solar first until it drops to the lowest usable temperature, then divert to the tankless heater or combi boiler.

    Typical residential DHW demands over there tend to be much lower so 50 gallons of solar, or a 100- 120 tankless or combi seems to be adequate for most homes.

    It's good to know what they expect before you plan the system. How much hot water and how quickly.

    With the tank first it could preheat, or send 120F to the Combi, once the 50 is depleted the combi would need to be able to cover the load on a continuous flow. That is why I would quiz them on how they use DHW now with two tanks.

    It hard to find a one size fits all DHW system. Possibly they could live with the Combi DHW production alone, ditch two tanks?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • Whichever heat source you pipe first will work the hardest because it is the first one to see cold water.

    Recirc. placement will make a difference, too. If you pipe the on-demand first and have the recirc. come back to the on-demand, your tank-type will never come on as long as the recirc. pump is on. The tank-type will lose its virility and effectively be a storage tank.

    All kinds of combinations and permutations.
    Often wrong, never in doubt.

    Click here to learn more about this contractor.
    CBRob
Sign In or Register to comment.

Welcome

It looks like you're new here. If you want to get involved, click one of these buttons!