"Summerizing" a hydronic heating system

Discussion in 'HVAC Heating & Cooling' started by wenglish, May 11, 2016.

  1. wenglish

    wenglish New Member

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    May 11, 2016
    Location:
    Edmonds, Washington
    Hello everyone, first post here (as you can probably tell).

    My condo was built in 2008, and some time before my unit was sold to the first buyer in 2010, the builder and the designer of the hydronic heating system both went out of business. I am trying to get a better understanding of the system, and the few HVAC people I called said I need to call the company that sold the system.

    Hot water goes from the gas water heater into a circulator pump (Grundfos UPS15-35SFC), and from there into a manifold that sends the heated water to each of the radiators. The return from the radiators then goes back into the water heater.

    The pump does not feed the hot water faucets, just the radiators.

    The circulator pump gets power when any thermostat calls for heat. It also gets power periodically from a wall-mounted 24-hour timer.

    My main question is why does the pump need to run daily?
    • For health reasons (making sure hot water doesn't sit for a long time in the pipes before going back into the water heater)
    • To prevent the pump from freezing (I mean mechanical freezing, not icing up)
    • No good reason
    I would like to disable the timer outside of the heating season, to save energy and to prevent convection of heat from the radiators when the pump is running (the fans on the radiators only blow when the thermostats calls for it). I don't want to destroy the pump by having it not run for 8 months. Or I'm OK manually running the pump for a while every week (say).

    Thanks ... Mike
     
  2. Tom Sawyer

    Tom Sawyer In the Trades

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    Maine
    the water in the heating system has nothing to do with the water at your faucets. The pump timer is likely a scheme to keep the pipes from freezing in sevear cold weather but it's a poor way to go about it. Better to fill the system
    With antifreeze
     
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  4. wenglish

    wenglish New Member

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    Edmonds, Washington
    The water that gets pumped through the radiators comes from the same water heater that supplies the faucets (therefore antifreeze would be a bad idea).

    It could be to prevent freezing, but we're in a pretty mild climate (Seattle), and they didn't put a pump on the (cold or hot) supplies to the faucets, so I think that is unlikely to be the reason for running the pump periodically.

    But I could be wrong. That's why I'm asking here :-D
     
  5. Dana

    Dana In the trades

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    It sounds like what is sometimes called an "open" heating system, where potable water is run through the radiation. That's not even legal in many states, but in those that are it's common to have a duty-cycling requirement to prevent stagnant water in the heating system from growing human pathogens during the months when the heating system is not in use.

    In most jurisdictions the heating system water would have to be isolated from the hot water heater water with a heat exchanger. On those systems there are two pumps that are active during a call for heat, one on the potable side of the heat exchanger, the other on the water heater side.

    Some "combi heater" hot water heaters have heat exchanger inside the water heater, so no exterior heat exchanger is necessary. Without a model number or a picture of your system there's no telling for sure what you have on your hands here, or if/how you might want to modify it.
     
  6. wenglish

    wenglish New Member

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    May 11, 2016
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    Edmonds, Washington
    Thanks Dana. The water heater is a Bradford White PDX250T6FBN, which (looking at the specs) does not appear to have a heat exchanger built in.

    However, the circulator pump has its own outlet from the tank (labeled "This connection is to be used for space heating only"), and the return also goes into its own inlet in the tank. But the booklet that came with it does not seem to talk about separate outlets for space heating, or about heat exchangers.

    I'm not looking to modify it or fix anything, I'm just looking to not destroy the pump if it needs to be run daily and if I unplug it for the summer. I'm also not looking for any more pathogens in my life, so I should probably just leave it as is (running for 30 minutes daily).

    Mike
     
  7. Dana

    Dana In the trades

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    Running the heating system even for 30 minutes in the summer isn't exactly great during the warmer weeks.

    The "right" thing to do would be to add a heat exchanger and another pump to isolate the potable from the heating system, eliminating the stagnation issue.
     
  8. wenglish

    wenglish New Member

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    May 11, 2016
    Location:
    Edmonds, Washington
    Thanks. Yes, that excess heat is what I'm trying to eliminate (I've got the timer set to run at 3am figuring that would have the least impact, I also turn down the water heater during the summer months which helps).

    So to double-check - not running the pump for (say) 8 months shouldn't be a problem for the pump itself?
     
  9. Dana

    Dana In the trades

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    The pump should be fine, assuming it's the right type of pump. If the pump is iron it might rust up, but iron pumps in potable water systems tend to have short lifespans anyway. Look up the model number on the pump and see what it's made of (on the inside).
     
  10. wenglish

    wenglish New Member

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    Thanks for all the help Dana. The pump (grundfos ups15-35sfc) is stainless steel. I'll research further on whether the water heater has a built-in heat exchanger or not.

    Mike
     
  11. wenglish

    wenglish New Member

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    Based on a diagram of this water heater, which labels the "space heating" outlet as "supply to heat exchanger", I am now confident the water heater does not have a built-in heat exchanger, so I'm going to leave everything as-is.

    Thanks for all the help.

    Mike
     
  12. Tom Sawyer

    Tom Sawyer In the Trades

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    If the tank has two separate toppings that say for heat then the tank has an exchanger in it.
     
  13. wenglish

    wenglish New Member

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    Thank you Tom.

    Mike
     
  14. Dana

    Dana In the trades

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    That isn't actually the case (would that it were!).

    There are a number of condensing and non-condensing hot water heaters designed with hydronic heating in mind that have no internal heat exchangers, and are often used in modest -load houses in the southern US in conjunction with hydronic air handlers, sometimes with, sometimes without isolating heat exchangers.

    The fact that the output side of the hydronic heating port is labeled "supply to heat exchanger" is a hint that it's anticipating being hooked up to an external heat exchanger. But why guess? On page 55 of the manual it's quite explicitly using potable water at the heating ports.
     
  15. wenglish

    wenglish New Member

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    OK, thanks, I think that settles it :)
     
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