Question on Water Heater Set-up - buffer tank size etc.

Having a new geo system installed, a Waterfurnace 7 series and need to figure out how to configure water heater(s). The install guide for waterfurnace suggests best results for using the DSH is with a buffer tank and I have read that elsewhere on this forum. I currently have an oil boiler hydro system that provides heating but also supplies hotwater through an indirect buderus logalux ST300 (80 gal) which I think could work as a buffer tank. This tank is ~10 years old but appears to be in good shape (given I can't see inside its plastic shell) and have had no problems with it. This tank has always provided enough hot water.

I have read in other discussions that in northern climates, it is better to have a smaller 50 gal buffer tank than a 80 gal tank. But I already own an 80 gal tank that i think (need to confirm) could be used as a buffer tank so a few questions:

Question 1: For a buffer tank should I:
A. Use the buderus 80 gal as unpowered buffer tank since i already have it or
B. Ditch the 80 gal and get a conventional 50 gal water tank as a buffer tank - efficiency of 50 gal over 80 gal out weights the fact I already own the 80 gal and it is 10 years old

Question 2: What size finishing tank?
- 50 or 80 gal? I am thinking 50 - having a buffer tank plus a finishing tank of 50 will provide the same or more hot water as the 80 given normal use for a family of 4.

Question 3: What type of finishing tank
- conventional or hybrid/heat pump? (I have heard that finishing tank electric use can be so low that getting high efficient model might not justify extra purchase cost)

Question 4: Or should I scrape the buffer tank and just install one 80 gal hybrid tank?

Any thoughts / suggestions and reasons appreciated.

Thank you in advance.

 

Use what you have, 80 gal for buffer and whatever size you want for finishing.

 

You need a buffer tank, otherwise the hot water will be inefficient.

So I would use the 80 gallon as buffer, and a heat pump water heater for finishing. Remaining energy cost is less with desuperheater, but with family of 4, and electric resistance heat, it is still too much.

 

Thank you for the replies. Very helpful. One more follow up. Do you think I should get a 50 gal tank or an 80 gal tank for the finishing heater?

 

Depends on your hot water use, More than 2 people, I would get an 80 gallon.