Any suggestions? Tankless water heater will use propane. 80 gallon buffer tank fed by 3 desuperheaters. 2,3 & 4 ton GeoMax 2.

Honestly, would just use a well insulated electric backup tank. Depending where you are electricity and propane are almost the same cost (it is here).

Agreed
I'm very reluctant to get on the tankless bus unless natural gas is available.

If in climate zone 3 or lower (possibly 4) consider also a heat pump water heater.

We have run this set up for the last 2.5 years with a lot of success. A 4 ton climatemaster with desuperheater run to a 60 gal. Hot water heater (not connected to electric using as insulated storage tank) then to a Takagi T-K3 propane tankless water heater.

I'm skeptical of the cost effectiveness of propane for any routine bulk heating task (water heating, clothes drying, space heating, cooking)

Propane is excellent fuel for standby generators and grilling meat anywhere natural gas is unavailable. Other than that, well, show me the money.

I installed a navien and have never looked back. Not storing hot water saved me money big time and the navien is sipping propane. My research bore out that the tankless upfront cost is only off set by the need for intermittant periods of high usage/ just like a vfd water pump. That is my condition.

As for brands? I found it boiled down to local support and mounting location. The rinnai type use the dual wall vent pipe at I think 46.00 for an 18" joint. That results in mounting those units in some pretty odd locations so that the installer can use the 1 supplied joint in the box that comes gratis. I chose navien for it's dwv pipe vent and intake due to my desired mounting location would have consumed alot of money for the 2 wall combo pipe.
Hope this helps
Eric

I have a Paloma made by Rinnai and I have had it for almost 4 years. I replaced an old 40 gallon electric tank on a Sunday after I was out of town fishing for 4 days. I came home to find no hot water and i needed a hot water ASAP. So I made the jump from electric to propane tankless. That was the only tankless hot water tank I could find, I got the venting and the unit for like $1100.

My electric bill went down about 50 bucks a month since the install. Now I never ever run out of hot water, and I only use about $25 to $35 of propane per month. I now have two children age 9 months and 4 years and we use a bunch of hot water. We do a load of laundry each day, wash the bottles each day and take lots of baths and showers. When I got rid of my electric hot water heater the cost of electric was 17 cents per KWH, now I am paying 14 cents per KWH. So now that electric is so cheap it may be cheaper per month, but not running out of hot water is very important to me.

With geothermal and no nat gas, I would consider a heat pump water heater in any climate.

Posted By jonr on 09 Oct 2012 09:36 AM
With geothermal and no nat gas, I would consider a heat pump water heater in any climate.

I would agree, why would climate have anything to do with the HPWH? It uses conditioned air.

In a far northern climate "conditioned" air means heated air most of the year - one pays twice - once to heat the room and again to heat the water. It is not an automatic disqualifier, but must be considered.

Posted By engineer on 10 Oct 2012 09:01 PM
In a far northern climate "conditioned" air means heated air most of the year - one pays twice - once to heat the room and again to heat the water. It is not an automatic disqualifier, but must be considered.

Agreed. We did the math on this once upon a time. At the very least found payback horizon out there a ways. Not necessarily a deal breaker, but a HPWH at 3 COP using heat created at 4 COP does not mean you are getting 7 COP .

The real deal breaker for many is going to be the recovery rate. Switching from gas to electric is bad enough in gph recovery. Switching to a HPWH can be brutal if you have high demand.

If the desuperheater is working, the recovery rate of a heat pump water heater will be much better than expected (edit: probably still not great). Operating cost, < 1/2 of electric or propane heaters.

Agreed - the "first hour rating" might better be called the "five hour rating", because once an HPWH is completely exhausted it can be 5 hours before it recovers in a northern climate with low ambient and low incoming water temps.

Put another way, an HPWH better have stored a home's complete morning or evening's total usage

Posted By jonr on 11 Oct 2012 02:23 PM
If the desuperheater is working, the recovery rate of a heat pump water heater will be much better than expected. Operating cost, < 1/2 of electric or propane heaters.

While true this ignores several other realities to support a particular position.

First- "if DSH is working"; 
A DSH does not always work. When it does work, it will improve the performance and cut operating cost of ANY tank down stream.
Second- "operating cost, <1/2";
Sounds like a terrific savings but may be under $50/yr after you deduct the btus that heat pump has to replace in the home.

Worse yet. If your heat pump doesn't have the extra capacity for the load of the HPWH you could actually have to replace those btu's with 1 COP auxiliary heat . Not likely but possible on cold days if geo is designed with high balance point.

So as I previously stated pay back may be out there a ways.
It may exceed the life of the product.

Lest we forget, these are relatively new products and compressors aren't big fans of super high temps. So those of you who want a compressor to make 130* water may not find Your HPWH lasts as long as a conventional electric storage unit, nor long enough to pay for the difference in price.

As I mentioned before we did the math on these, and they generally come down on the plus side. They are not going to be a good fit everywhere or pay back the additional expense. I certainly wouldn't want one where I had a high balance point.
They are a much better fit in areas Engineer mentioned.

First- "if DSH is working"; A DSH does not always work

Exactly why that phrase is there.

Second- "operating cost, <1/2";
Sounds like a terrific savings but may be under $50/yr after you deduct the btus that heat pump has to replace in the home.

Obviously, that was accounted for, otherwise it would be ~1/3.

While true this ignores several other realities to support a particular position.

Other than the usual misrepresentations and wrong statements, sounds like Joe agrees, a HPWH is something to "consider" (what I wrote), not a universally correct choice.

"Other than the usual misrepresentations and wrong statements"

Come again.

I think I clarified the detractors adequately and honestly.

I think 3 COP would be much to hope for in a northern basement in January even if you ignored the cost of make-up heat.

The homeowner and plumber are adamant about using a tankless water heater and Im tired of trying to explain the benefits of two electric tanks (buffer and finishing). This house will also have 10kw of photovoltaics feeding it.
No natural gas so propane is being installed for stove and fireplaces. I guess what I should have asked is what tankless works best with high incoming water temps.

I think that the Takagi T-K3 can have incoming temps from the DSH extremely high, ie 150 or so. My Paloma gets upset if the incoming water temp is higher than 120, my DSH never ran long enough to get the 50 gallon buffer tank up to that. However it did get up to high 70's and that cut my propane bill a bunch.

So look at the Takagi models and the Navien models. My tankless was purchased well before I ever thought about getting geothermal.

The ones that allow the lowest min btu rates. But unless it goes right down to zero, there is always an incoming temp where certain output temps are impossible. Plan on some uncomfortable showers with a DSH/tankless combination.

Posted By joe.ami on 11 Oct 2012 10:17 AM

Posted By engineer on 10 Oct 2012 09:01 PM
In a far northern climate "conditioned" air means heated air most of the year - one pays twice - once to heat the room and again to heat the water. It is not an automatic disqualifier, but must be considered.

Agreed. We did the math on this once upon a time. At the very least found payback horizon out there a ways. Not necessarily a deal breaker, but a HPWH at 3 COP using heat created at 4 COP does not mean you are getting 7 COP .

Of course not! - Coefficients are multiplicative, not additive, so instead of 3 COP + 4 COP = 7 COP, it is 3 COP X 4 COP = 12 COP!

Something like that, anyway...