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Thread: Circulation Pump Operating Cost

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    DIY Senior Member molo's Avatar
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    Default Circulation Pump Operating Cost

    This is a technique to heat water with a wood-stove. I would consult a few professional plumbers prior to installing a system like this.
    Question: How do I determine the cost to operate the pump? I'm wondering if it is going to be an unjustified conversion because of pump operating costs.

    Thanks for any input

    http://www.hilkoil.com/Technical.htm
    "Any American who is prepared to run for President should automatically, by definition, be disqualified from ever doing so."
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    Retired Defense Industry Engineer jadnashua's Avatar
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    Most circulators are farily small pumps, drawing less than 100W. Taco makes a bunch, and you can view their spec sheets www.tacohvac.com (there might be a hypen between taco and hvac).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the Trades Bob NH's Avatar
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    The pump power is going to be one of the least of your problems.

    The problem with putting a coil in a wood or coal stove is that there is no control of the temperature.

    Water boils at 212 F, meaning that the steam pressure at 212 F equals atmospheric pressure of 14.7 psi absolute.

    At 350 F, which is well within the range of a fire in a wood stove, the gauge pressure is 120 psi. That is much greater than the pressure of your water supply so the steam will force water back into your supply system. In a hot fire of 450 F the pressure will exceed 400 psi and there is considerable danger of bursting copper piping and/or failing solder joints.

    The relief valve will prevent overpressure but that will dump a lot of hot water in an uncontrolled way.

    The temperature/pressure relief valve in a water heater relies on having the hot water at the temperature-sensing stem, which will not be in the hottest part of the wood stove.

    The safety issue is why many residential wood-fired boilers use vented (atmospheric pressure) tanks that can't build up any pressure. You could safely run the water-heater coil through such a tank, but it is not safe to simply put it in the firebox.

    A tankless coil in an oil-fired boiler works because the boiler has a temperature control that limits the heating and the tankless coil is immersed in the water of the boiler.

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    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by Bob NH View Post
    The pump power is going to be one of the least of your problems.

    The problem with putting a coil in a wood or coal stove is that there is no control of the temperature.

    Water boils at 212 F, meaning that the steam pressure at 212 F equals atmospheric pressure of 14.7 psi absolute.

    At 350 F, which is well within the range of a fire in a wood stove, the gauge pressure is 120 psi. That is much greater than the pressure of your water supply so the steam will force water back into your supply system. In a hot fire of 450 F the pressure will exceed 400 psi and there is considerable danger of bursting copper piping and/or failing solder joints.

    The relief valve will prevent overpressure but that will dump a lot of hot water in an uncontrolled way.

    The temperature/pressure relief valve in a water heater relies on having the hot water at the temperature-sensing stem, which will not be in the hottest part of the wood stove.

    The safety issue is why many residential wood-fired boilers use vented (atmospheric pressure) tanks that can't build up any pressure. You could safely run the water-heater coil through such a tank, but it is not safe to simply put it in the firebox.

    A tankless coil in an oil-fired boiler works because the boiler has a temperature control that limits the heating and the tankless coil is immersed in the water of the boiler.
    Not to mention the endless hours of cutting wood unless you plan on buying it and if you buy it what have you saved.

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    DIY Senior Member molo's Avatar
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    Quote Originally Posted by Bob NH View Post
    The pump power is going to be one of the least of your problems.

    The problem with putting a coil in a wood or coal stove is that there is no control of the temperature.

    Water boils at 212 F, meaning that the steam pressure at 212 F equals atmospheric pressure of 14.7 psi absolute.

    At 350 F, which is well within the range of a fire in a wood stove, the gauge pressure is 120 psi. That is much greater than the pressure of your water supply so the steam will force water back into your supply system. In a hot fire of 450 F the pressure will exceed 400 psi and there is considerable danger of bursting copper piping and/or failing solder joints.

    The relief valve will prevent overpressure but that will dump a lot of hot water in an uncontrolled way.

    The temperature/pressure relief valve in a water heater relies on having the hot water at the temperature-sensing stem, which will not be in the hottest part of the wood stove.

    The safety issue is why many residential wood-fired boilers use vented (atmospheric pressure) tanks that can't build up any pressure. You could safely run the water-heater coil through such a tank, but it is not safe to simply put it in the firebox.

    A tankless coil in an oil-fired boiler works because the boiler has a temperature control that limits the heating and the tankless coil is immersed in the water of the boiler.

    Hello Bob and thank you for your response regarding safety.

    I am aware of the potential disaster and death that an improperly designed and installed wood heated water system can cause. This particular technique (putting a tube in the firebox) does require alot of attention. Would the use of an aquastat work to insure the water circulates and stays cool enough?

    If this idea is just not feasibly safe, I would consider an "open" system.
    Here is a unit made in vermont that is patent pending and attaches to the outside of the stove, perhaps safer. I would like to know your or anyones opinion on the use of this or other techniques to heat water.

    I have an ample supply of firewood here in the Northeast, and don't mind the exercise to cut it.

    http://www.wipo.int/pctdb/en/wo.jsp?...6&DISPLAY=DESC

    http://cgi.****.com/Hot-Water-Tank-W...QQcmdZViewItem

    Thanks,
    Molo
    "Any American who is prepared to run for President should automatically, by definition, be disqualified from ever doing so."
    Gore Vidal.

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    In the Trades Bob NH's Avatar
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    The Aquastat could control circulation but the problem is that the heat must be dissipated or the whole water heater could exceed the safe temperature.

    The Aquastat in a normal boiler controls the temperature of the boiler by controlling the fuel. It turns off all of the fuel when the water in the boiler reaches the controlled temperature.

    A wood stove can be shut down by limiting the air but the temperature doesn't drop quickly.

    An open boiler is safe because it evaporates the water when the temperature reaches 212 F and dissipates the heat with steam. Each pound of steam lost carries away about 1000 BTUs of heat.

    If you put a coil in the stove and connect it to a non-pressurized or low-pressure tank outside the stove, preferably working as a thermosiphon, and then circulate your domestic hot water through a coil in that tank, you could do it safely. The external tank could also supply a circuit for heating the house through low-pressure steam or circulating hot water.

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    DIY Senior Member molo's Avatar
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    Thanks for the response Bob,

    The thermosipohon is an attractive option. It would eliminate the need for a pump. Do you have any suggestions for finding engineering info. for thermosiphon designs?

    TIA,
    Molo
    "Any American who is prepared to run for President should automatically, by definition, be disqualified from ever doing so."
    Gore Vidal.

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