Can I use my indirect water tank with my heat pump water heater?
Hello, I currently have a boiler-fed, indirect water tank that supplies our domestice hot-water. To avoid $5/gal oil cost and short-cycling the large boiler during the 6 months of non-heating months I decided to invest in a 50 gal heat pump water heater. My question: can I plumb the new water heater so I can use the indirect storage tank as additional hot water storage space? The hope would be to allow additional hot water capacity for my family. Thoughts?
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The simplest would be to plumb the indirect in line with the HPWH downstream of it (coldwater ->HPWH->indirect->house). From the drain of the indirect connect a small pump (recirc ones are fine) to the drain of the HPWH. The recirc pump can be driven by the existing controls.
The idea is that in most cases the indirect is just a holding tank, as long as the HPWH has enough hot water in it, all the water going into the indirect will be hot. The only time the recirc should run is to make up for standby losses when there is no water flow.
The better option is to sell your indirect and buy a plug in 120V tank water heater. Set this up the same way after the HPWH and set the thermostat on it to a bit bellow your HPWH output temperature. This way the extra tank would only use power to make up for standby losses or if ever there is a large enough water draw to empty out both tanks.