I'm building a new home and need help deciding how and what to use to heat water. I'm installing a bosch 6 ton (nominal) system ECM variable speed, vertical, 2 stage. My local electric utilities offer a great rebate on the systems of $750 per ton but you have to install a electric water heater. They also offer great prices to members on marathon heaters. Should I add a desuperheater and use just the marathon? Use the desuperheater and marathon as a storage unit for something else (hybrid heater)? Just use either the hybrid or marathon on its own? I live in Kansas City, and am new to all this so sorry if I misspoke on something, just trying to make my house as efficient as possible. Thanks!

6 tons is alot. what is the load for the house? If the price is low enough, go ahead and use the Marathon as a finish tank and use the DSH.

Remembering that I'm new to this I'm assuming you mean the electric load?

6 ton (Nominal) System ECM variable speed
Vertical Heat Pump-2 stage 410A
19.2 kW Supplemental Heat
Hot Water Recovery Kit
Concentric Fitting for Hot Water
Ground Loop Pump - Composite
Connector Kit 1"
Pump to Loop Adapter Fusion

It's a 5,500 sq ft two story. The basement is unfinished so only 3100 finished feet

3100 heated space ---- 6 ton unit --- does not make any sense. (or is the basement being heated as well?) What Joe was asking - what does your Manuel J say the heating/cooling load is?

Yikes is that based on cooling load or something? Does your installer have a lot of geo experience?

The basement is unfinished now, but yes sorry it's heated and cooled also. Yea they have a lot of experience. Why is it too big?

I think it's just that with new builds the level of insulation and air sealing let's you install smaller heat pumps.

Having an un-powered buffer/storage tank for the desuperheater, connected to a heatpump water heater would work great. Just have to be sure the HPWH can take being fed warm- hot water.

Chris

New construction in my area (North Florida) can come in at 1500-2000 SF / ton with proper attention . KC is a bit tougher climate, but I should think that yours could come in at 1000-1200, making a 4 ton a more logical choice. Of course, that's site unseen.

Investment in high efficiency water heating (DSH, buffer tank, heat pump water heaters) should be guided by the number of full time residents planned for the home. An empty nester couple might be better off foregoing the fancy stuff in favor of a simple electric tank heater. OTOH, a family of 6+ should go all in.

Don't bother spending on the DSH option without also installing a dedicated unfired preheat tank. Taken together cost could be $1500, and that doesn't include finishing water heater(s)

Thank you so much for the info. I'm not sure if this helps with the oversized question but we didn't have the space for horizontal wells, and not much space for vertical. We are drilling 4 400 ft wells

We don't know for sure it's too big without knowing heat loss/gain (manual J load). But it seems a typical for modern construction.

Even with super efficient houses we are 650 sqf/ton in houses under 2000 sqf. Larger houses are more efficient per sqf, but we never are over 800 sqf/ton in single story houses. Climates are different up north, or in Kansas in the middle of winter.
A second story usually only adds about 5,000 BTUs/h, so in this case I assume 1900 for the first floor, and 1200 for the second floor. A code minimum insulated house that size in Kansas should be around 4 ton with forced air. Adding the basement might add another 1/2 ton, for a total of 4 1/2 tons. Six tons sounds a bit excessive to me as well. Have your load checked and calculated. 4x400ft also sounds excessive for the borehole. Even for 6 tons. 275ft/ton? What kind of geology do you have. Concentric fitting for hot water raises the red flag. Does your installer plan one or two tanks? Including a buffer tank? And on top of all this 20 KW supplement heat?

I would do a desuperheater in almost every case. If you can do the majority of your hot water with the efficiency of the geosystem? As Joe says, only for singles or empty nesters, who might be Snowbirds living in Florida in the winter, the hot water consumption might be so low that it is not worth it. In all other cases, we also see a value ofr the customer in a hot water generator.

Code minimum is the worst constructed and performing house one can legally get away with building. It is a bare minimum one expects in starter homes and speculative McMansions. Code min has no place in custom builds.

I'm no fan of insanely insulated Passive Houses or paying the LEED Clipboard Raj to document how every piece of cardboard generated by construction site goes to Recycle Heaven, but anyone having a custom home built should consider adhering to "pretty good house" standards, typically 50-100% above code minimums, and employ blower door directed air sealing before drywall goes up.

Those reasonable measures should substantially increase SF / ton resulting in markedly lower first cost for geo system and substantial energy svaings baked into the life of the home.

A competent local energy rater ought to be able to provide the blower door testing as well as identify low hanging / high ROI fruit to lower project's HERS score and lifetime total cost of ownership.

Energy Star used to be a reasonable target, but compliance costs to attain Tier 3 come at a sufficiently diminished return that many builders have bailed. Still, Tier 3 sets forth performance metrics worth attempting to attain.

Posted By engineer on 25 Jan 2014 10:02 PM
Code minimum is the worst constructed and performing house one can legally get away with building. It is a bare minimum one expects in starter homes and speculative McMansions. Code min has no place in custom builds.

I'm no fan of insanely insulated Passive Houses or paying the LEED Clipboard Raj to document how every piece of cardboard generated by construction site goes to Recycle Heaven, but anyone having a custom home built should consider adhering to "pretty good house" standards, typically 50-100% above code minimums, and employ blower door directed air sealing before drywall goes up.

Those reasonable measures should substantially increase SF / ton resulting in markedly lower first cost for geo system and substantial energy svaings baked into the life of the home.

A competent local energy rater ought to be able to provide the blower door testing as well as identify low hanging / high ROI fruit to lower project's HERS score and lifetime total cost of ownership.

Energy Star used to be a reasonable target, but compliance costs to attain Tier 3 come at a sufficiently diminished return that many builders have bailed. Still, Tier 3 sets forth performance metrics worth attempting to attain.

Curt, I think this is exceptionally well worded.

Best regards,

Bill

Thank you.

I'm not particularly proud of the single run-on sentence comprising paragraph two, but it will serve.

Our protocol parses a structure or project into "energy centers", to include envelope, HVAC, water heating, lighting, refrigeration, cooking, laundry, pumping, and miscellaneous loads and identifies cost-feasible alternatives specific to client's situation.

A few examples:

1) While we love desuperheaters and heat pump water heaters, 1-2 person households are often not good fits.

2) It is folly to trip over a single speed 2 HP pool pump set to run 12 hours per day on the way out back to measure for a high SEER heat pump

3) new windows rarely make sense, but screening, filming or shading select west glass is often a no-brainer.

4) Putting a 15-20 year old side-by-side frig in a hot garage is insane.

5) Don't cook with gas indoors.

6) Don't consider solar-anything until all reasonable conservation steps are taken.

Posted By engineer on 26 Jan 2014 09:04 AM

Our protocol parses a structure or project into "energy centers", to include envelope, HVAC, water heating, lighting, refrigeration, cooking, laundry, pumping, and miscellaneous loads and identifies cost-feasible alternatives specific to client's situation.

A few examples:

1) While we love desuperheaters and heat pump water heaters, 1-2 person households are often not good fits.

Why?  What's magic about 1-2 people that then changes when it's 3+ people?


2) It is folly to trip over a single speed 2 HP pool pump set to run 12 hours per day on the way out back to measure for a high SEER heat pump

Amen.  I changed mine two years ago.  This is a 'no brainer.'


3) new windows rarely make sense,
 
Agree unless existing window(s) are already broken (which happens here in Dallas often - vacuum seal breaks)

but screening, filming or shading
 
Amen

select west glass is often a no-brainer.

And East and South in summer, IMO.


4) Putting a 15-20 year old side-by-side frig in a hot garage is insane.

Amen.  Make it a goal to get to one refrigerator, as big as needed, that's of latest technology.


5) Don't cook with gas indoors.

Why?  Don't understand this one.


6) Don't consider solar-anything until all reasonable conservation steps are taken.

Amen.  Or 'wind-anything.'


Other examples?

Curt, please see above comments.

Thank you.

Best regards,

Bill

Posted By engineer on 25 Jan 2014 10:02 PM
Code minimum is the worst constructed and performing house one can legally get away with building. It is a bare minimum one expects in starter homes and speculative McMansions. Code min has no place in custom builds.

I'm no fan of insanely insulated Passive Houses or paying the LEED Clipboard Raj to document how every piece of cardboard generated by construction site goes to Recycle Heaven, but anyone having a custom home built should consider adhering to "pretty good house" standards, typically 50-100% above code minimums, and employ blower door directed air sealing before drywall goes up.

Those reasonable measures should substantially increase SF / ton resulting in markedly lower first cost for geo system and substantial energy svaings baked into the life of the home.

A competent local energy rater ought to be able to provide the blower door testing as well as identify low hanging / high ROI fruit to lower project's HERS score and lifetime total cost of ownership.

Energy Star used to be a reasonable target, but compliance costs to attain Tier 3 come at a sufficiently diminished return that many builders have bailed. Still, Tier 3 sets forth performance metrics worth attempting to attain.

Just to clarify, I was implying that even a code minimum house this size in KC, not knowing this particular insulation status, should not require a 6 ton system. I was not implying that someone should build a code minimum house!

So MJ if what we suspect is true your contractor may be adding tons of insurance capacity to your job, inflating duct work size (which takes space from other things) needlessly adding thousands to the cost. Unless you have a West window wall, I can't see the need for that much.
Again however we are not privy to the load calculations.
I agree with Doc that the concentric water heater connection made me suspect inexperience in the installer as well, however manufacturers still offer them as valid so someone who doesn't try different things or monitor their equipment may not know better.

Yea I'm not sure, They may have oversized the system. They came with a lot of experience and good referrals that I called on. I'm blowing in all my exterior walls(2x6) with pink pro l77 fiberglass and r-38 in the attic. I also installed a air seal caulk and foam trout the house. Maybe the high ceilings are contributing? I have 10 ft ceilings in the basement, main floor and upstairs with each of the 4 bedrooms being vaulted higher than that. I think with my hot water needs I will use a standard 50 gallon as a storage tank hooked up to a 85 gallon marathon. Thank you all for the input.

That doesn't sound like a high performance envelope, but still...........