I am new here but want to pose a question that may have been hashed over several times. I am building a 3000 sq ft house w/ very high end windows and insulation (2x6 w R21 or foam) . Here is my quandry- pay an extra $12,000 for geo that may not pay off for years esp. w/ cap and trade driving elec $ up or save the 12K and put in 95% eff Trane and spend some of the savings on spray foam upgrade?? Roof is going on next week and it is time to decide. I have plenty of room for loops (5ac) and am aware of the 30% tax credit but this offset by the whole loop mess and hassle.

Help

To start there is way to little info to give an acurate answer.

But 2 points first it will never be cheaper to install geo then it is now , i.e. likely at least a backhoe is on site allready

and your future yard is not prestinily landscaped .

2nd point on C&T there is no reason to expect that fossil fuels ( the target of cap and trade ) will not rise at the very least equally to electric .and yes I have read about it .

 

All that being said NG and good insulation is the NEXT best thing in many parts of the country

The performance difference in an air-tight house between R21 (batts?) and half-pound foam won't be huge as long as it's truly air-tight by attention to detail (caulking and sealing every penetration, gluing the interior wall to the studs, etc. Do you have any insulative sheathing for thermal breaks on the framing? (and is it too late to put some on the outside? If so, is it too late to put an inch of ISO or XPS on the INSIDE, under the gypsum?) Is the basement fully sealed & insulated? (Insulated concrete forms? EPS on the foundation exterior, anything?)

There are many ways to spend 12K to dramatically reduce the heat load, depending on the state of the shell design & construction.

Wet-spray cellulose won't cost much more than batts (might even be less), but will fill every nook & cranny thus sealing better. An inch of panelized foam goods (inside or out) will effectively double the R-value of the framing's thermal short-circuits from ~R5.5 to ~R11, increasing the whole-wall R-value (framing shorts included) from about and effective-R15 effective to a true R21 (assuming it's 24" on center. You'll be a couple lower for 16" oc framing). A 2" half-pound spray foam insulate & seal on the foundation sill & band joist is a couple grand, make a HUGE difference in the air-tightness. Foam sealing all of the attic floor/conditioned space is even cheaper, also important. In some cooler parts of the lower 48 of the US, R21 batts in 2x6 is barely code-minimum these days, not a premium- what's your zip code?

High efficiency heating systems are great, but high-efficiency building envelopes have a longer lifecycle, and it's cheaper to build-in the envelope efficiency than it is to retrofit it. All else being equal, the high-efficiency envelopes is a better deal. But without the particulars of your heat gain/loss it's hard to say what makes the most sense for you at this juncture. But going for super-insulation (like double the code minimums, with full foundation & slab insulation as well) insulates you against the cold wind of energy price increases pretty much forever, no matter what the efficiency of your heating system. (The better the building envelope, with the diminutive size & cost of the mechanical systems their relative efficiency becomes irrelevant.)

If your local electricity is 75% coal-fired, you may be in for some ratcheting power costs, but unless they're 30cents/kwh or more the operational cost of geo will be less than even high-efficiency NG. If you're lucky enough to be somewhere that you can get a Climate Energy co-generator/furnace combi that may be the cheapest overall (since it'll severely offset your other electricity costs while heating your house.) See:

http://www.freewatt.com/products.asp?id=169&name=WAir

The system will be a several grand more than a gas-fired furnace, but less expensive than geo. (The guy in the office next to me has the hydronic version at his ~5500ft^2 house, installed as a retrofit. IIRC it set him back ~$18K-installed, but it will have paid for itself in under 5years between fuel + electricity savings. We currently have some of the highest power rates in the lower 48. If you live in coal-fired 8cents/kwh-country it's not nearly as good a deal, but still might be the "right thing do do". Clearly YMMV.)

Thanks Dana, I will have to check out the freewatt system- how new is this?

We have 1/2" of xps (greenboard) then another 1/2" coming w/ siding on the outside- I wanted to help reduce bridging (really wanted SIPs).

We are definitely using closed cell foam on the headers in the basement, and in the roof deck over the bonus room. The rest was a caulk and seal package with R21 batt including the basement(finished). I didn't put XPS on outside of basement due to what I read on the rapid loss of R value when buried.

With the XPS on the outside and the R21 inside we will be at R26. R-50 in the attic- blown cellulose.

BTW we are in SE Michigan- fermi nuke plant is electrical source. I would go with solar on the roof but- It's Michigan

Having all ductwork within the conditioned envelope makes a substantial difference in load and cost of operation.

High density sprayfoam installed properly is about as airtight as any method and it also increases structural strength. I'd be less confident of the airtightness of conventional methods because there are so many details to get right and that are tedious to do right, so it is probable that some details will be missed.

The measured performance of batts tends to be much lower than the nominal R-value owing to a host of material and installation issues, some of which have already been mentioned

Superior insulation may save you 10% of the load, but geo may save you 200-300% on conditioning the load. While Dana is correct that modifications to the envelope require virtually no maintenance, geo requires less than gas furnaces.
I really don't get the loop objection with a lot that is likely torn-up already (as GF points out). Or a disregard for a tax credit that could make the system cheaper. Yes cheaper.
We work in your area and in an apples to apples comparison there's no way a horizontal geo should cost $12,000 more than a high efficiency furnace and air. My guess would be closer to 5-$8,000 more (depending on the man. J load).
I've yet to meet a geo installer that builds code minimum duct work but many fossil guys will. Make sure whatever system you choose will heat and cool your new home in a way that makes you comfortable or all the insulation in the world is worthless.
Good luck,
Joe