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Q&A Reflector and PT relief for DHW - Heating Hot Water with Sto

Post in 'Questions and Answers' started by QandA, May 26, 2007.

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  1. QandA

    QandA New Member Staff Member

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    Question:

    SPECIFIC QUESTIONS ON HEATING DOMESTIC HOT WATER (DHW) FROM A WOOD HEATER Well be augmenting DHW heat with wood heat in the winter. We are getting a big masonry wood burning heater with a heat collector loop in it; a 40 long 1 I.D. Stainless Steel U will be mounted in the top. Could you make any recommendations as to how to ensure we never have a dry very-very hot pipe in the heater and introduce cold liquid into it? We could have a steam explosion and I dont know if a regular TP relief valve could keep up with it. I know GFI ground fault interrupt switches exist for electric lines. Does something like this exist in a water valve? Normally, when the outlet pipe is warm, an aquastat would start a pump to move liquid through the loop in the heater. If there was some failure, the inlet and outlet pipe would get very-very hot and Id like some way to permanently shut of fluid to the line until we investigated the reason for the overheat.

    I've heard that high mineral content can cause pipes to get crudded up with gunk in heat exchangers. Do you think this applies to my wood heater loop? We will know more after we have our water tested for mineral content.



    Answer:

    Pressure relief valves are made for this type of situation. A properly rated valve (probably about 150K BTU or more for your application) is capable of taking care of any and all steam that would be built up in such a situation. Also, because some valves are temperature and pressure, they would always blow before things got too bad (pressure rises with temperature). Be sure to pipe the output of the TP valve to an area where it will not blow in anyones face, etc. Do not have any shut-off valves between the heating coil and the TP valve.

    Another idea would be to use a 40 gallon or larger tank mounted near and above this loop (if this fits into the building plans). Then, you could set up circulation without a pump or aquastat, assuring flow even if the power fails.

    We have not had any problems with our loops getting clogged up. Hot water storage tanks should probably be flushed out every two years or so to remove sediment from the bottom.

    Article at http://www.hearth.com/what/woodstovedhw.html that might help ou further

    Link: Article on Hot Water from your stove...

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