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Victor S. Lyle
Starting Member

1 Posts

Posted - 05/10/2015 :  10:01:49 PM  Show Profile  Reply with Quote
Looking to replace water heater with a new model, I am looking for a Conventional hot water storage tank. Currently I own an oil fired peerless boiler with an output of 107,000 but to feed the unit and have a home of 5 people that need to shower, wash dishes and perform laundry during the day. When performing the calculus, I cannot seem to determine which would be more efficient, a smaller unit such as a 30 gallon, which falls within the beta input requirements for the boiler, but is on the verge of the first hour rating or increasing to a 35 - 45 gallon unit which exceeds the first hour rating requirement but is over sized for the boiler. Would the purchase of a larger unit is a dissipation of money or would it be better to have a larger unit for the water storage with the understanding that the boiler would need to run more to keep up with the unit. Any input would be greatly appreciated.

Advanced Member

789 Posts

Posted - 05/11/2015 :  09:36:35 AM  Show Profile  Reply with Quote
It primarily depends on your use of the hot water. If the five people want to take a shower and do the laundry all at the same time, you need a big tank, else somebody will end up with cold water. Conversely, if the need for the hot water will have no dramatic ups and downs, a smaller tank should suffice. The energy cost should not differ too much or at all, because the thermal loss will occur through the same piping, assuming both tanks have the same insulation.

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EVIL Teken
Advanced Member

2354 Posts

Posted - 05/11/2015 :  1:19:52 PM  Show Profile  Reply with Quote
You could simply install a smaller HWT tank and plumb the instant hot water tank inline. The benefit depends upon your use case and how you intend to use the resource.

For me my plan is to use it as a *Booster* opposed to an extender. In a booster arrangement you dial back the TSTAT on the HWT to a lower (safe level) which you then let the tank less instant hot water (IHW) unit heat the incoming water supply to the preferred temperature.

The benefit of this is that during idle times the standard HWT is set to a much lower level. Which directly translates to less KWH consumed during the day. While the IHW provides endless hot water which is supplied by the smaller reserve tank.

That is a win win situation, lower energy cost and endless hot water. In the *Extender Mode* you simply leave the HWT at the same hot temp as the IHW unit. Essentially the unit would provide a buffer to the smaller reserve tank until it ran out of hot water.

The difference is that the smaller buffer tank would come on heating the incoming water to the exact same temp, while the IHW was doing the exact same thing. This would extend the hot water supply for quite a long time.

This is my plan moving forward in the next year and that is to use the *Booster* method. Because my goal is about saving money not so much about having endless hot water. Because I only have a small family and the massive tank in my home is much too big to ever run out.

Teken . . .

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Starting Member

5 Posts

Posted - 09/02/2016 :  9:04:27 PM  Show Profile  Visit williamjames's Homepage  Reply with Quote
Well, it totally depends upon your hot water usages. To calculate the size water heater you need, evaluate capacity versus consumption. Compare water tank capacity or continuous flow rate to peak usage rate. Showers are the key. Multiply the showerhead flow rate by the average length and number of showers in a given period of time.

Edited by - williamjames on 09/02/2016 11:52:25 PM
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