# Thread: Conventional vs Hybrid Heat vs Geothermal - Am I Right?

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## Conventional vs Hybrid Heat vs Geothermal - Am I Right?

I've been doing a lot of research lately regarding an HVAC system for the house we are building. As the biggest investment of my life, I want to make sure I get it right. At this point in time I'm leaning toward Geothermal, but can't seem to get an unbiased calculator to help me figure costs. I tried my best, and here are the results!

Location: Outside Green Bay, WI
Status: Hole dug, foundation poured
Home size: 1st - 2028sqft 2nd - 857sqft Basement - Unfinished, will finish later!
Orientation: Facing North, most windows on South side
Insulation: 2x6 with R-23 BIBS, R-50 attic, foam attic seals, foam box sills
Electric Cost: \$.12
Gas Cost: \$1.25

Conventional Gas Furnace & A/C
Carrier 58MVC Variable speed 95% AFUE
Carrier 13 SEER A/C
3 Zones
Infinity Control
RenewAire ERV

Carrier Infinity Hybrid Heat System
Carrier 58MVC Variable speed 95% AFUE
Carrier 25HNA6 16 SEER Heat Pump
3 Zones
Infinity Control
RenewAire ERV

WaterFurnace Geothermal System
WaterFurnace Envision ND064 ECM w/ horizontal 2 pipe .75" PE
7 foot depth and 200ft of trench/bore
Electric auxiliary internal duct heat 11kW
Envision ND dual capacity Series Water Unit
Electric with GeoAsist Water Heater
2 Zones
RenewAire ERV

The cost of the Hybrid Heat system is about 15% more than the conventional system, and the Geothermal system is about 50% more than the conventional system. (This is hard to do without mentioning prices!)

I calculated that the Hybrid Heat system would save me about \$300/year over the conventional system. I calculated that the geothermal system would save me about \$1200/year over the conventional system. Do those numbers seem reasonable? Using those numbers I came up with a payback period of about 7 years on the hybrid heat and 6 years on the geothermal with the geothermal system outlasting the air source heat pump by about 10 years and ultimately saving more money.

Please feel free to poke holes in the logic, thanks! I can provide house plans or other information if more is needed.

2. I wonder if some of your annual savings figures, especially with the geo, could be a bit high.

Also for the size of the house in a moderate climate, new construction, good insulation and mostly south windows, 53K heat gain seems really high.

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Thanks! That's the kind of info I'm looking for. Can I ask why you think the savings estimates may be high? Just to provide more info, I can tell you that \$75/year of the \$1200/year savings is water heater savings.

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I sat down and ran through numbers with a bit more rigor last night and here's what I came up with.

Conventional Gas Furnace & A/C
Carrier 58MVC Variable speed 95% AFUE
Switched to Carrier ANA7 17 SEER
3 Zones
Infinity Control
RenewAire ERV

Annual Cost to operate: \$2520

Carrier Infinity Hybrid Heat System
Carrier 58MVC Variable speed 95% AFUE
Carrier 25HNA6 16 SEER Heat Pump
3 Zones
Infinity Control
RenewAire ERV

Annual cost to operate: \$2453

WaterFurnace Geothermal System
WaterFurnace Envision ND064 ECM w/ horizontal 2 pipe .75" PE
7 foot depth and 200ft of trench/bore
Electric auxiliary internal duct heat 11kW
Envision ND dual capacity Series Water Unit
Electric with GeoAsist Water Heater
2 Zones
RenewAire ERV

Annual cost to operate: \$1651

So...the Hybrid Heat savings becomes \$67/year. The Geothermal savings becomes \$869/year.

That pretty much eliminates the Hybrid system in my opinion. It's a 29 year payback period for the upgrade.

The payback period for the geothermal becomes 8.3 years and will provide a benefit of \$14512 from then until year 25.

Does that seem closer to reality?

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Check out the Dept. of Energy website. They removed the 1500.00 cap from the 30 percent tax CREDIT on geothermal heat pumps til 2016. There is nothing in that section for conventional or dual fuel (hybrid)... It should make your decision simple. Also my ranch is a bit bigger than yours. I have a 4 ton WF with hot water assist and 15kw aux. heat. For 2008 my electric was 1607.00...Based on your footage, I think your annual cost for geo looks really close...Go for it, you won't regret it..

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Thanks for the reply, I really appreciate it.

After the dealer realized I wasn't just wasting his time he conducted a more thorough manual J. The new numbers came back in even lower with the more detailed calcs.

If the numbers I have above are accurate it doesn't seem like a difficult decision. The numbers I ran already take the tax credit into account. Without it the geo system is almost twice the cost of the standard system.

7. psm
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## \$67

With the significant shoulder seasons in WI I'm having trouble understanding why the HP is only saving you \$67/yr. I would think that it should be supplying a significant amount of heat in those seasons at a cost considerably less than gas. I'm trying to make exactly the same decision and am having a bit of trouble coming up with annualcosts of operating the hybrid system.

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Originally Posted by psm
With the significant shoulder seasons in WI I'm having trouble understanding why the HP is only saving you \$67/yr. I would think that it should be supplying a significant amount of heat in those seasons at a cost considerably less than gas. I'm trying to make exactly the same decision and am having a bit of trouble coming up with annualcosts of operating the hybrid system.
PSM, I used this calculator to determine the savings:

http://sagoro.wrightsoft.com/Carrier/Default.aspx

9. psm
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Thanks 'thenuke'. That was exactly what I needed.

10. Don't forget to factor in the 30% fed tax credit. You cannot put the dollar amount your gonna invest ( in a geo ) in a bank or the stock market and get a 30% return in the first year, Forbes magazine also had an article about the positive return on your investment in a geosystem. Plus lower water heating costs, greater comfort and positive cash flow from your investment. No stock market account will do that.

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Thanks for the reply GeoDude. The 30% tax credit is already figured in there. If that weren't in there I'm not sure the thing would pay itself off in its useful life!

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So I'm almost ready to pull the trigger on the Geo, but a few things have changed that I wanted to post here and ask for suggestions.

Originally our contractor didn't want to use a Slinky, but after looking at the lot in person and using some software to calculate it he decided to use 12 60' trenches with 500ft of slinky in each (1000/125tr 18" pitch). That seems like a lot of trenches and a lot of tube! 6000ft! Will it be more costly to run a system with so much tubing, even if it is split into 12 trenches?

He has also decided that an ND049 (4-ton) is more suited for the home than the orignal 5-ton, because of the recalculation of the load calcs. Loads went from about 80k heat and 53k cooling to 60k heat and 25k cooling. The overall house is 4,913sq ft. with plans to finish about 4000. (about 2900 initially, and another 1100 in the basement later) Those numbers seem very low to me for such a large space. Anyone else see any reason to be concerned?

He seems to be doing everything by the book with calcs, loop lengths, etc. and now I'm the one speculating...imagine that.

I've attached the load calcs to see if anyone notices any red flags, as I've never seen one before.
Last edited by thenuke; 04-07-2009 at 01:26 PM. Reason: Going to retry the upload, as it wasn't legible.

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While I'm at it I may as well post two of the pages from his proposal. What should I be looking for here?

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