I've already posted a few times, but here is a summary of my situation. I live in Essex MA, and recently purchased a 2100 sqft ranch. The ranch is heated by electric baseboards, has a full attic and basement, and sits on about 2.3 acres of flat land. I've tried pretty hard to find a contractor to install geo for me at my target price of <$30k. Currently most of the bids I've received are in the $36-$40k range. Bids have ranged from 4-ton to 5-ton.

In MA we have a program sponsored by the utility company to improve our home's insulation but taking attic insulation up to R-38 and performing air sealing ot 62.5 CFM50 per hour. This will be done on my home this week. I had a chance to speak to the insulation contractor, and he offered a few additional services while he is on the job. First, he offered to take my attic to R-60 for an additional $700. Second he offered to install spray foam insulation in my basement for $1125 to cover 500 sqft of wall area - a rate of 2.25/sqft. As I understand it, there are diminishing returns when insulating above a certain amount, so my question is whether it is more sensible to put the extra $$ into the basement which is entirely un-insulated as opposed to taking the attic to R-60 instead of R-38? By my calculations, the heat loss of R-38 vs R-60 in my attic should be 3,400 BTU/hour vs 2,200 BTU per hour. Like I said, my basement is not insulated at all and my foundation perimeter is roughly 180ft. I've been told that above grade foundation has a U-factor of ~1 which would mean that taking 500 sqft of the foundation to R-12 or so might make a great impact on my heating loads. Is my logic correct? Any input is greatly appreciated...

Your logic is spot on- insulating the basement & band joist is by FAR a higher priority than taking an R38 attic up to R60! (I'd be surprised if there's even enough vertical space to take that attic all the way to R60 at the eaves in the first place, and if it's tapering down to R30 at the edges the R60 in the middle hardly matters, since the heat loss at the perimeter 2' will dominate the heat loss out of the attic, not changing a huge amount even if you took it to R1000 in the center.)

Since code requires an ignition barrier on the cc foam in the basement, building out a studwall to carry the necessary half-inch gypsum and putting in cheap unfaced R11 or R13 batts takes the R12 up to about R20 without a lot of undue expense. If you're only insulating the top half with spray foam, its still worth insulating the bottom half with something cheap (like 2" reclaimed roofing EPS) to a comparable thickness before putting up a studwall or furring for gypsum. The design frost depth in your area is still something like 55", and by the end of the winter the bottom of the foundation wall can be pretty cool, representing a real heat load.

Putting it another way:

At R38 the roof is probably on the order of 10% of the total heat loss, and going to R60 only peels off 3-4% from the total tonnage of the GSHP- it hardly matters since it's less than a quarter-ton delta.


At R1 the above-grade portion of the basement is on the order of 16-20% of the total heat load and taking it to R13 (concrete + foam), taking at least 15% off the size of the system, and could easily be more than 1-ton.

With 500 square feet exposed foundation at a U-factor of 1 and a delta-T of 50F (55F basement, +5F outside temp) would be 25,000 BTU/hr more than 2 tons of load. 500' of ~R12 continuous foam (~ U0.085) and a 60F delta (65F basement, +5F outside temp) is a measly 2550 BTU/hr, a reduction of nearly 2 tons. Even if the U-factor of the above-grade basement & band joist averages closer to U0.5, representing a heat load of only bit over 1-ton, you're essentially eliminating that ton of load.

With an infrared thermometer take a few measurements of the foundation wall about 2' below grade some morning after a frosty night between now and Thanksgiving and you'll probably find it's about 50F, maybe even below 50F. And if you insulate only the top half of the wall, by the end of the winter mid-winter coolth the uninsulated half the wall be as low as 55F on average. A 55F wall in a 65F room is losing well over 15 BTU per square foot (approaching 20BTU/ft) whereas the insulated R15 upper half is only losing ~5BTU/foot even at +5F (and much less on average.) If we take a WAG that you have about 750' of below-grade foundation wall, that lower half is worth more than half ton of GSHP load by the end of the winter even if it's only losing 10BTU/ft, and insulating it to R8 (2" of EPS) takes off a half-ton of load or more.

Ok, the insulation is complete. The installer gave me a break and took my attic up to R-57/60 for a decent price and air sealed. The house came in at 1,450 CFM after air sealing which he said was pretty good. He suggested to go the rigid foam route in the basement and to just use spray foam on the band joist. Can anyone comment on whether 1,450 CFM is decent? I'm guessing I'm well on my way to 3-tons of geo ...

1450cfm/50 is not super-tight, but it is indeed pretty good. The foundation sill and band joist are typically the biggest unseen untreated air leak in semi-tight houses- you may be under 1000cfm/50 after after you foam the band joist & foundation sill, not that's it's worth re-testing (unless you're going for some level of certification, or can get a better subsidy or something.)

In a 2100' ranch house with a 2100' basement might be 18' from slab to ceiling , and enclose total volume of about 35,000 cubic feet inside the thermal & pressure boundary of the house, so at 1450cfm or 87,000 cubic feet per hour, the ACH/50 number is 87K/36K= 2.5 ACH/50. Code max on new construction in MA is currently 7ACH/50. It will drop to 3ACH/50 once IRC2012 becomes code, but you already have that beat with some margin. After sealing & insulating the band joist you'll probably be hitting at or under 2ACH/50 (the Canadian R2000 max spec.) Really, anything under 3ACH/50 is pretty good, from an energy use point of view, especially on single story homes with minimal stack effect drive.

Professional energy-nerd Marc Rosenbaum's fairly well insulated & sealed place on Martha's Vineyard came in at ~900cfm/50 before he took a weekend to chase down leaks with the aid of a blower door, peeling it back to ~650cfm/50. (See: http://blog.energysmiths.com/2011/03/whats-a-renter-to-do-air-sealing-can-be-low-cost-and-effective.html ) Those are both VERY tight numbers compared to typical construction. By contrast a buddy of mine's even bigger house (3 story 3-family with full basement) came in at about 450cfm/50 after a deep energy retrofit. That's SUPER tight, but it took a serious amount of air sealing detailing throughout the full-gut rehab (and they used 2x more closed cell foam than I was recommending.)

Bottom line, you're cruising on the right track!