# advice on retrofit geothermal system



## andrewjoseph (Oct 30, 2015)

I have been getting bids on a new system to replace my 29 year old ground loop geothermal unit. The company that I trust the most and have used in the past has given me some advice that I cant find much info about online.

They recommend that I replace my 29 year old water heater with a new plastic marathon heater. He said that I would not want all od the junk circulating between a brand new unit and a old potentially rusted or corroded water heater.

They said they would put a new water in for me or I could they it and put it in myself. They didnt appear to want to sell the water that badly at all. He just said he would not spend the 12 thousand on the furnace and compromise it with the old water heater.  the new geothermal unit will have a desuperheater on it, which is why this idea came up.

Is this good advice? 85 gallon rheem marathon is about $1400 at menards with tax, and there is a 11 percent rebate now.

Thanks for any help you guys might give.


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## maple1 (Oct 30, 2015)

How much $ does the desuperheater add to the cost of the system? I don't have geo, but have heard comments from some that do who weren't overly impressed with the performance of their desuperheater. Was there one on the old unit? How was it if so? That is an expensive water heater.


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## velvetfoot (Oct 30, 2015)

I wonder how it would compare to a standalone air source heat pump?


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## woodgeek (Oct 31, 2015)

RE ASHP, I would thing the geo is a good choice, given the climate and the ground loop (which I assume will be reused and is properly sized).  

If I had a geo, I would want a logging system and/or some way to assess its performance.  Is this standard now?

I would compare pricing on (1) the desuperheater + marathon versus (2) no desuperheater and a HPWH like the geospring.  The latter would likely have competitive performance (might be better), and HPWHs are commodity items (re cheap, discounted) whereas DSHs are not.


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## andrewjoseph (Oct 31, 2015)

My price for the entire new geothermal system is $9700 including desuperheater. Then I will be able to receive a credit for approximately $2900 on my taxes for 2015. Superheater was not itemized, so I am unsure of the price. 

I have noticed a lot of these water heaters being put in new homes, but never knew much about them. I guess the advantage is that the tank will never need to be replaced. Only the heating elements, which wont really be used 5 months out of the year.

If the tank truly is a lifetime purchase and will help make my geothermal system run better/longer Im all for it, I just cannot find much online to back up this strategy.






maple1 said:


> How much $ does the desuperheater add to the cost of the system? I don't have geo, but have heard comments from some that do who weren't overly impressed with the performance of their desuperheater. Was there one on the old unit? How was it if so? That is an expensive water heater.


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## andrewjoseph (Oct 31, 2015)

andrewjoseph said:


> My price for the entire new geothermal system is $9700 including desuperheater. Then I will be able to receive a credit for approximately $2900 on my taxes for 2015. Superheater was not itemized, so I am unsure of the price.
> 
> I have noticed a lot of these water heaters being put in new homes, but never knew much about them. I guess the advantage is that the tank will never need to be replaced. Only the heating elements, which wont really be used 5 months out of the year.
> 
> If the tank truly is a lifetime purchase and will help make my geothermal system run better/longer Im all for it, I just cannot find much online to back up this strategy.


We have a desuperheater on our current unit and it seems to work great. I have turned of the breaker to the water heater for a few weeks just to test it out, to see if its really heating. Seems to be hot, just not as fast as a water heater heats. The unit is from the beginning designs, so I am thinking the technology now will be even better.


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## andrewjoseph (Oct 31, 2015)

woodgeek said:


> RE ASHP, I would thing the geo is a good choice, given the climate and the ground loop (which I assume will be reused and is properly sized).
> 
> If I had a geo, I would want a logging system and/or some way to assess its performance.  Is this standard now?
> 
> I would compare pricing on (1) the desuperheater + marathon versus (2) no desuperheater and a HPWH like the geospring.  The latter would likely have competitive performance (might be better), and HPWHs are commodity items (re cheap, discounted) whereas DSHs are not.


Thanks for the reply. I checked geospring water heaters, and people seem to like them. But it is $999 at lowes for a 50 gal and is a 10 year tank. I have soft water here and would likely get more years on it.  The marathon I priced is an 85 gal (we have 5 people living here, 4 are girls) for $1260 counting the menards rebate. 

I dont mind spending a bit more for the tank - which is supposed to never need replacing. I like the desuperheater on the current system, and dont think it adds that much to the price anymore. I will check on that though Monday.


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## andrewjoseph (Oct 31, 2015)

velvetfoot said:


> I wonder how it would compare to a standalone air source heat pump?


I would need a supplemental electric furnace installed in the basement also. It gets too cold here for at least two months out of the year for the air heat pump. Plus I have the loops already in place and my contracter believes it to be correctly sized.

For $6800, counting tax credit, I dont think I can justify switching to another type of system where I need two units installed. My current system has lasted 29 years, which I partially attribute to being protected from the elements year round.


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## semipro (Oct 31, 2015)

OP, I"m curious, are they using your existing ground loops?


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## woodgeek (Oct 31, 2015)

andrewjoseph said:


> Thanks for the reply. I checked geospring water heaters, and people seem to like them. But it is $999 at lowes for a 50 gal and is a 10 year tank. I have soft water here and would likely get more years on it.  The marathon I priced is an 85 gal (we have 5 people living here, 4 are girls) for $1260 counting the menards rebate.
> 
> I dont mind spending a bit more for the tank - which is supposed to never need replacing. I like the desuperheater on the current system, and dont think it adds that much to the price anymore. I will check on that though Monday.



You should also consider operating costs for total cost of ownership (over, say 10 years).  The geospring will save roughly 50% on your energy bill vs the marathon.  In a typical house (on a 12 mos basis) this would be $200-400/yr (depending on HW usage and electricity costs).  If you got 50% of your water from the DSH, you would still save $100-200/yr with the HPWH and after 10 years that would dwarf the difference in upfront cost.

Looks like you are high HW user, so would want to go bigger than the 50 gal geospring.  Myself (two teen girls), I got a 80 gal HPWH from AOSmith, MSRP is ~$2k, before rebates.  But if you figured you would save >$200/year vs the Marathon (as a high HW user), you would make back the difference in initial price in 3-4 years.  The AOSmith unit has a powered anode (rather than a sacrificial one) so the tank should last a very long time, and has a good warranty.


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## semipro (Oct 31, 2015)

woodgeek said:


> The AOSmith unit has a powered anode (rather than a sacrificial one) so the tank should last a very long time,


Curious, how is a powered (impressed current) anode better?  Wouldn't a properly maintained sacrificial anode offer the same protection?


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## woodgeek (Oct 31, 2015)

Just to add to your questions....there is the sizing issue.  If you have an older house that has not been energy audited or airsealed yet, you can probably drop your BTU heating load 20-30% for a few thousand dollars.  If so, you could downsize the tonnage on the geo, and perhaps get a cheaper unit.

A smaller unit on the bigger ground loop would also likely hit a higher efficiency figure operating, COP.


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## woodgeek (Oct 31, 2015)

semipro said:


> Curious, how is a powered (impressed current) anode better?  Wouldn't a properly maintained sacrificial anode offer the same protection?



If both anodes maintained enough voltage to prevent tank corrosion, sure.  But, believe it or not, most people don't maintain their anodes....they just replace the whole tank a year after the anode rots out.  Because, you know, thats easier.


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## maple1 (Oct 31, 2015)

andrewjoseph said:


> We have a desuperheater on our current unit and it seems to work great. I have turned of the breaker to the water heater for a few weeks just to test it out, to see if its really heating. Seems to be hot, just not as fast as a water heater heats. The unit is from the beginning designs, so I am thinking the technology now will be even better.


 
Do you have any idea on how much it cost to heat your DHW with the desuperheater in the summer?

The comments I referred to earlier about some with geo being disappointed with their desuperheater had two aspects - slow recovery, and cost to run.

I think I would investigate not getting the desuperheater, and just heating my DHW with a HPWH. Or even an ordinary water heater. Our ordinary resistance tank heater only costs $20-25/mo to run (@ $0.18/kwh) and it only cost $350 to buy.


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## velvetfoot (Oct 31, 2015)

I meant in my earlier post HPWH vs desuperheater, sorry.


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## semipro (Oct 31, 2015)

woodgeek said:


> If both anodes maintained enough voltage to prevent tank corrosion, sure.  But, believe it or not, most people don't maintain their anodes....they just replace the whole tank a year after the anode rots out.  Because, you know, thats easier.


Thanks. So, does the unit let you know if the cathodic protection circuit is not working?

BTW: I"m one of those people that does replace their sacrificial anodes.  I've got one heater going on 30 years even with hard water problems.


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## moey (Oct 31, 2015)

I would strongly suggest you buy 2 40 gallons from the big box store. One is a buffer that works with the geo system the heating elements are turned off on it. The problem with no buffer is the elements are still doing most the work even on cold days. If its 40F outside the elements are doing all the work as your heat is not running enough to make hot water before the elements come on. Sure you can shut the breaker off on in Jan and Feb but you lose out on Nov, Dec, Mar, Apr with a buffer tank you can still make 40 gallons of 100-110F water the 2nd tank then raises the temp 10 degrees. DSH work slow so the elements kick their a$$.

The other option is a heat pump water heater.

The option I would not recommend is what your contractor recommended you will see little to no benefit with a single 80 gallon tank. Its unfortunate the manufactures show a single tank setup in the install manuals. Its a way to sell more DSH's.

I think DSH add about $500-$700 to the heat pump cost. 

If your old tank made it 29 years theres no need for a Marathon. Your water must be pretty close to neutral. Its probably a good idea to replace it at the same time.


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## maple1 (Oct 31, 2015)

moey said:


> I would strongly suggest you buy 2 40 gallons from the big box store. One is a buffer that works with the geo system the heating elements are turned off on it. The problem with no buffer is the elements are still doing most the work even on cold days. If its 40F outside the elements are doing all the work as your heat is not running enough to make hot water before the elements come on. Sure you can shut the breaker off on in Jan and Feb but you lose out on Nov, Dec, Mar, Apr with a buffer tank you can still make 40 gallons of 100-110F water the 2nd tank then raises the temp 10 degrees. DSH work slow so the elements kick their a$$.
> 
> The other option is a heat pump water heater.
> 
> ...


 
Do you have a Geo system? I'd like to hear more from those who have one and a desuperheater and how much they cost to run to heat their DHW with, say on those shoulder months or in the summer. I'm not sure how accurate the talk I heard was. Maybe they didn't have their system set up right or something, if that's possible. I think they were expecting more out of it than they got, for whatever reason, mainly in the summer.


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## moey (Oct 31, 2015)

maple1 said:


> Do you have a Geo system? I'd like to hear more from those who have one and a desuperheater and how much they cost to run to heat their DHW with, say on those shoulder months or in the summer. I'm not sure how accurate the talk I heard was. Maybe they didn't have their system set up right or something, if that's possible. I think they were expecting more out of it than they got, for whatever reason, mainly in the summer.



I have a geo system. I dont have a electric monitor. I have one tank and when I got it I was sold on it making my hot water. In the summer we dont run our A/C enough maybe 10-20 days a year and the run times are not that long. The system needs to be in a steady state before the DSH even starts running. Its not producing the superheated gas that the DSH uses to make the hot water. So often in colder climates your don't get much in the summer. Temperatures also are lower in the summer for the superheated gas so without a buffer tank in the summer you will get nothing you'll make 100F water maybe slightly less. The DSH will come on and then shut off as the temp of the tank most likely will be hotter. Thats where a second tank comes in to play. 

In colder climates you have to consider its only making hot water when the system is running. Most the summer your not running your A/C. 

Ive never got around to getting a second tank I would like to. Last year I shut the breaker off mid Dec and turned it back on in mid March. There were a few days I had to turn the breaker on when it got into the 40s. 

There are quite a few system on this page:

http://www.buffalogeothermalheating.com/sample_diagram.html

Heres one with a DSH monitoring there probably are more:

http://welserver.com/WEL0601/

I think if you look in the install manuals they will give you btu output of the DSH compare that number to the elements its easy to see who wins with one tank.


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## DBoon (Nov 1, 2015)

I can't comment on de-superheater vs. no de-superheater (DSH), but on the topic of the Marathon tank - that is a good tank and would be a good choice if your water is very soft since soft water will corrode your anode protection quicker.  If I had a 29 year old water in my house, I would be replacing it too - it is probably built way better than the 12-year life models that would replace it, which is why I would go with the Marathon since there is no glass-lining in the Marathon to fail. 

The air-source HPWH is the way to go if you have high humidity in your basement and would run a dehumidifier down there anyways (or should be running a dehumidifier).  Some can even have the cool air ducted to supply AC to the house in the summertime, if you wish.


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## sloeffle (Nov 2, 2015)

We have a geo system with a DSH that has a 50 gallon Marathon hooked to it. We also have a A.O. Smith HPWH.

IMHO, not unless you plan on using the Marathon to make hot water I wouldn't spend the extra money on it. I didn't thoroughly read all of the previous posts, so this might of been mentioned before. You will not reap the benefits of the DSH unless you have two tanks. The problem with the single tank system is that hot water heater heats the water up faster than the DSH does. So that defeats the purpose of the DSH.

I would give a little different advice than @moey. I would get the cheapest 80 gallon electric hot water heater I could buy and hook that up to the geo. I think of that tank as a battery bank, the bigger the better. I would then hook up in series a 50 gallon HPHW. Our HPHW saves us roughly $50 a month over having the Marathon make hot water. And I no longer need to run a dehumidifier in my basement. Our A.O. Smith HPHW was 1k. We will have our money back in under 2 years. I would opt for the A.O. Smith Voltex ( better warranty and better energy factor ) over the Geospring. But I am not a big GE fan either.

Scott


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## maple1 (Nov 2, 2015)

sloeffle said:


> We have a geo system with a DSH that has a 50 gallon Marathon hooked to it. We also have a A.O. Smith HPWH.
> 
> IMHO, not unless you plan on using the Marathon to make hot water I wouldn't spend the extra money on it. I didn't thoroughly read all of the previous posts, so this might of been mentioned before. You will not reap the benefits of the DSH unless you have two tanks. The problem with the single tank system is that hot water heater heats the water up faster than the DSH does. So that defeats the purpose of the DSH.
> 
> ...


 
Just wondering - if one was to get the HPWH, why then would the second 80 gallon electric heater be needed or wanted? Doesn't the HPWH also have elements for when demand is higher than the HP can output?

Or is it because you use a LOT of hot water? I might be remembering you saying that before, actually, and thinking you must if you're saving $50/mo....


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## sloeffle (Nov 2, 2015)

maple1 said:


> Just wondering - if one was to get the HPWH, why then would the second 80 gallon electric heater be needed or wanted? Doesn't the HPWH also have elements for when demand is higher than the HP can output?
> 
> Or is it because you use a LOT of hot water? I might be remembering you saying that before, actually, and thinking you must if you're saving $50/mo....


Sorry, I should've been more specific on my last post.

I would turn the elements off on the 80 gallon tank ( In a two tank scenario ) and let the DSH heat the water. If you have problems with the HPHW you can simply just turn the elements on and have hot water again. As far as I know all HPHW have elements that you can turn on manually. My HPHW has a hybrid mode that will turn the elements on if the air source heat pump cannot keep up.

Our family of three averages around 100 gallons of water use per day according to our last water bill. I have no idea what percentage of that is used for hot water.


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## woodgeek (Nov 2, 2015)

A HPWH does have elements, but has different operating modes.  I set mine to HP only for max savings, and recovery is slow when the space (my garage) is cool.  If I have a houseful of guests over, I set it to 'element' mode and we're all good.

I've got the 80 gal Voltex


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## DBoon (Nov 2, 2015)

Just for clarification, my comment on the Marathon is specifically around the durability. I don't want to risk a puddle of water (or more) in my basement, so I choose to have something that has essentially zero chance of every leaking.


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## sesmith (Nov 12, 2015)

We have a geo system with DSH and 2 tank system.  The tank for the DSH is just a standard 40 gal electric hot water heater with the electric elements not hooked up.  Talk to your installer on the ideal size, but I'm not sure I'd go much larger than 40 as the DSH will use some of your heating energy to operate in the winter months.  There is no reason to maintain and heat an 80 gal DSH tank unless you really need that much.  A 40 gal DSH tank in series with a 40 gal hot water heater is a lot of hot water.   Do some research, but I think you'll find that a 2 tank setup is the recommended way to set up a DSH for the best efficiency.

For us, the DSH supplies almost all our hot water during the heating season, and very little of it during the non-heating season, as we don't use ac a lot.


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