Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Mixing valve setup A or B which way?

Joebif Member Posts: 51

Since my last post I found a investor that is going to purchase a large wood fired boiler that requires a 500 gallon storage tank so we can get the most BTU's we can out of the wood boiler.

I am looking at putting in a mixing valve on my existing propane water heater. I had 2 thoughts on were to put the mixing valve and wanted to get some input from the experts on what your thoughts are on its placement.

Drawing A would bring the heated water from the storage tank in front of the propane water and allow the heated storage water to be used to feed the system. I am wondering and asking if this way is okay to do but had a question. If the heated water is warmer than the water coming from the propane water heater will I only use the propane water heaters water? If it is colder then it would use the storage tanks water and mix in what it needed from the propane water heat to make up the difference. My purpose is to not have to use the propane heater that much and only use it as a backup in case the storage water heat is not up to the heat it needs.

Drawing B would bring in the heated water from the storage tank in the return side of the propane water heater. If it is hooked up this way and the water is warmer in the storage tank than the water in the propane water heater would it pass through the propane water heater and thus not heat it thus saving me the energy of propane? If the water were colder than the propane water heater then the storage water would get heated enough to be what was needed for the system.

Please put in your opinion on A or B.

Or do you have a C or D please let us know.


  • hot_rod
    hot_rod Member Posts: 16,327
    what temperature

    do you want to supply to the heating? Can you run the heater at that temperature without condensing? If so the heater should feed directly into the radiant without going thru the 500 gallon storage. The 500 should only be heated by the wood boiler.

    One method is a diverting valve with a differential control. If the 500 is 120F or warmer, for example, then the flow is from the 500 tank.

    When the 500 drops the flow diverts thru the backup heater.

    Now you might need a means to mix down the temperature from the 500. for that you need a 3 way thermostatic mix valve.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Joebif
    Joebif Member Posts: 51
    Mixing valve is the title

    I have the mixing valve as my title and it is in both drawings so I am confused with your opinion.

    But to answer your question yes I want to supply to the heating. The propane water heater is being used for radiant heat so it will be about 140 or 160 degrees.

    In my drawings I thought that it was set up so only the wood boiler is heating up the storage and I want to feed the storage to the radiant heat.

    I was thinking that the storage heat would go above the propane heater heat so that is why I am asking about the mixing valve position.

    So with that what would you use A or B or should there be a C with differential control as hot rod suggested?
  • LarryC
    LarryC Member Posts: 331
    How is water going to get back to the 500 gal tank?


    In both of your schematics, you do not show how water is going to get back to the 500 gal. water storage tank.

    You could treat this as two separate heat sources operating in parallel.  Each heat source has a circulator pump and a single check valve.  Tie the two heat sources into a common header / manifold / hydraulic seperator / tank.  Draw from the combiner with a pump and tempering valve that uses the emmitter return water as the cold source.  Control the firing of the propane heater when the output water coming from the storage tank is less than your setpoint. 

    I am assuming the system will be vented to the atmosphere.  Is the 500 gallon tank outside?  Will it require freeze protection?  If so, did you account for the lower heat capacity of the water due to the antifreeze content?
  • Joebif
    Joebif Member Posts: 51
    Water getting back to tank

    I would like to use the water coming from the radiant return to be able to first go to the wood boiler. I will use the boiler only in the winter so I will have a ball valve on the return side of the water heater so it can be used to go to the wood boiler and not the propane water heater. Then in the summer change the return back  to the propane heater.

    I will not need antifreeze

    The reason I have the 2 drawings is this is all plumbed in and I need to add the storage tank setup with the mixing valve at the point that would be the easiest  and best way to do it.  I do not want to have to redo a lot of things.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    DIverter on the return, mixer on the supply between wood and aux.

    If you hit the water heater with extremely hot water (greater than 160) you will "discover" the ECO (energy cut out) fuse that is not resetable/non replaceable to the tune of $300.00+

    I'd put the tempering valve between the wood boiler and the water heater to protect the water heaters ECO switch ..

    I am going to have to think about how you will pump and pipe it to make sure everything works as planned. You don't want to have the LP heater dumping heat into the wood storage tank.

    What happened to the open system design?

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Joebif
    Joebif Member Posts: 51
    edited September 2011
    Open Design

    Mark, are you saying then use A? Are you also saying to use a diverter?

    I am to new at this and not sure exactly how to draw the open system and use this with what is there right now. If you or someone can help draw this I would maybe do it and use the funds for something else. 

    The drawings in A & B are what is plumbed in right now, except for the mixing valve. That would need to be cut in and re-done in these drawings. If you could help with an open system I would draw whatever I needed to and talk to you about helping you on anything.
  • Joebif
    Joebif Member Posts: 51
    Correction Mixing valve in B not A

    I miss read your post Mark. Then use B so the hot water from the storage tank, if over 160, can never enter the propane heater. The mixing valve in B will be set to 160 or 165 and thus protect the propane heater from ever getting higher than that.  I will put in a temperature probe in the line so I can visually see the temperature coming into the water heater so I know the mixing valve is working correctly.

    I do not understand then why or how the propane heater would be able to put heat into the storage tank. If the hot side is going to the radiant system will it come in from another area?  I thought the mixing valve would stop it from coming back to it or do I need a check valve or one way valve on the out of the storage tank to the mixing valve?
  • hot_rod
    hot_rod Member Posts: 16,327
    edited September 2011
    What type of wood boiler?

    some brands require a return temperature protection valve. The mixing valve assures the boiler does not run too cold and condense. This is a conceptual drawing that shows a wood gasification boiler with a back up.

    The back up heater may also need return temperature protection if you have a high mass radiant application for example.

    So you need a means to provide the required temperature to the heating distribution, A means to protect the heaters from cold return protection, and a means to toggle from one source to another. that can be done manually, or with some controls like a solar differential controller. the piping and control does get more complicated as you add more requirements.

    I don't see how a single three way valve can give you all the functions I think you are asking for?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
This discussion has been closed.