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Hot Water Supply Makeup Feed

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by HeatFarmer, Dec 1, 2011.

  1. HeatFarmer

    HeatFarmer Member

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    So here's my wacky thought...... Use DHW to feed in as supply side make up water. Traditionally this hasn't been done for the obvious reasons...energy cost & scale, etc from the boiler. With my system, the DHW comes off a coil inside the heat bank, so the energy cost is negligible and because there is no boiler, there is less scale, etc. I also don't want cold water diluting my supply to the heat-bank. I could put the makeup water into the return line, but I would like to feed it into the system through an air scoop to try to get as much air out of the system as possible before dragging it thought the radiator loops.

    Am I off base in thinking using hot DHW to feed into the system will help keep heat bank temps up, and not cause any further problems. Is there a fault in my logic?

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  2. maple1

    maple1 Minister of Fire

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    Not exactly sure on what you're asking - are you talking mixing DHW with heating system water? Pretty sure that's not a good idea if so.
  3. HeatFarmer

    HeatFarmer Member

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    This is technically what I am suggesting....but there would be separation via a back flow preventer....I'm merely using it to fill the system and then maintain the water level....


    But why? What difference is it to add warm water to a hot water stream, then to inject cold water on the supply side and chill everything down?
  4. rkusek

    rkusek Minister of Fire

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    How often do you plan to add make up water to your boiler system? When you says heat bank what are you referring to, some type of electric resistance heater? I don't even have a connection between my boiler and water system for fear of contamination if a back flow preventer fails. I tracked pressure and added water manually while fighting a couple small leaks last year. This summer I maintained pressure which means I finally got them all stopped. If I find a cheap RV type 12V demand pump with a pressure switch I may connect this to a 55 gal plastic barrel of water and connect to my boiler. This is probably not necessary but if I ever had an overheat situation that dumped the water this would replendish it. Other than the first filling, loss due to a leak, or loss due an overheat you shouldn't have to add makeup water. I can't think of any reason to preheat it in these circumstances.
  5. Frozen Canuck

    Frozen Canuck Minister of Fire

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    If you need to add enough water to make this a consideration.....chances are you have a leak somewhere in the system. Just a thought as you may be chasing the wrong problem.
  6. maple1

    maple1 Minister of Fire

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    OK, I think I see what you're saying - and no, I can't see any difference in plumbing the boiler supply to hot water rather than cold, if you wanted to. But I still don't see any advantage to it. Properly set up, the only time water should enter the boiler feed is at initial fillup, unless you spring a leak. I don't think there is a maintaining of water level - any water entering would be compensating for a loss somewhere that will need to be fixed.
  7. HeatFarmer

    HeatFarmer Member

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    Thanks to everyone answering my question. It was mainly a hypothetical one. I don't have system leaks...as of yet--Still planning the piping runs. Nor do I foresee a regular time when adding water would be necessary. However, I can see the point of plumbing this in for future expansion. Of, for instance....adding a zone to a Mother-In-Law apartment which might get turned off or drained down during the winter when she snowbirds down South..... It would then be a simple matter to add water in the spring or fall while the system is already up and running. Is it worth the $75 for a valve, some pipe, a back-flow-preveter & a water pressure regulator, for a once and a while occurrence? ...Probably not, in this economy.
  8. maple1

    maple1 Minister of Fire

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    Not likely, no - you would have to compare that to the cost of heating up whatever amount of water the zone holds, which I suspect would be negligible. Then that would be offset by the cost involved in heating the DHW that you would be inputting - which all else being equal should be the same as heating the cold water inputting into the system. It would have to be heated one way or the other.

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