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Indirect Storage for HW

BosSteve Member Posts: 1
I am looking for a piping schematic for adding a storage tank to an oil fired tankless coil.  I also need a wiring scematic for the aquastat.  I plan on using an electric hot water tank as my storage tank.  Any help would be appreciated. Thanks.


  • icesailor
    icesailor Member Posts: 7,265
    WH Storage:

    If you are using a water heater for the storage tank, like an electric water heater, pipe the hot and cold to the water heater full sized like you were going to connect it as an electric water heater. That usually means 3/4" in and out. Between the cold water inlet valve and the cold water inlet to the tank, install a 1/2" connection. Remove the drain from the bottom of the tank and replace it with a 6" brass nipple, a 3/4" brass tee, a 3" brass nipple and ell and whatever brass nipples you want to use. Buy a Taco 006BT bronze threaded circulator. The extra nipple and ell is to offset the circulator away from the bottom cover and make it easier to access the wiring. They now offer a stainless steel one but be sure it is threaded. Install the circulator with the arrow pointing up. Pipe this to the "cold" side of the tankless. Pipe the "hot" side to the top of the water heater where you left the 1/2" connection. I install valves and unions and a 1/2" check valve above the circulator but it is an option for you but not for me..


    There are many ways to do this. I'll give you the third world way. You can modify it with knowledge.

    Remove the lower cover. Remove both wires from the lower thermostat. It is going to be a "switch". Use a "Cord Whip" or for a really third world connection, if you have a dead extension cord, and the male end is OK, cut it off. Connect the white wire to the appropriate neutral in the circulator, the black wire through the water heater thermostat and the other end back to the "hot" wires on the circulator. Make sure you connect the green ground wire to the provided green screw on the circulator. Set the thermostat on the water heater to whatever you want. 130 degrees seems nice.  Change the boiler controls. Set the "Low Limit/Circulator" to 140 degrees. Set the "High Limit to 160 or 170 degrees.

    You are good to go.

    If the water in the tank needs to be hotter, turn up the temp, on the tank. If the house doesn't heat up as fast or enough, turn up the high limit. That will only be a problem in the coldest months.

    You will notice that the water will be hotter in the winter when the heat is cycling. In the summer it will be cooler because the boiler will be on the operating control and the boiler only will start when the water heater circulator calls.

    You do not need any other controls to make this work. You can go nuts and try to re-design the world but this has worked for me and my customer for a lot of years.

    As far as specific hot water storage tanks, when I built the house I live in now, I had to have it plumbed by others. Who did a fine job. I told them to use an electric hot water heater for a storage tank. They lost their mind. I shoe=wed up one day and found a "John Wood" hot water storage tank installed. Piped as per their instructions. Which I find, don't work as well as the way I have written. I changed it to the way I have described. I just replaced the tank after 10 years. I bought an AO Smith regular 50 gallon electric hot water storage tank. It is the same as the John Wood tank without the 1" plugs in the element holes. In 40 years of doing this, I have never had a leak through the elements.

    Electric water heaters are the cheapest insulated water heater tank you can buy.

    You can get all nuts and fancy and use the internal tank wiring but you must understand how the wiring and controls work. The easy way is the one I describe. The thermostat is a switch to control the circulator. The boiler control reacts to the drop in temperature. There is no physical, electrical connection between the two. It is already set up to do so.
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